Sample & Buy Product Folder Support & Community Tools & Software Technical Documents Reference Design LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 LM3424/-Q1 Constant Current N-Channel Controller with Thermal Foldback for Driving LEDs 1 Features 3 Description * The LM3424 is a versatile high voltage N-channel MOSFET controller for LED drivers. It can be easily configured in buck, boost, buck-boost and SEPIC topologies. In addition, the LM3424 includes a thermal foldback feature for temperature management of the LEDs. This flexibility, along with an input voltage rating of 75 V, makes the LM3424 ideal for illuminating LEDs in a large family of applications. 1 * * * * * * * * * * * LM3424-Q1 is an Automotive Grade Product That is AEC-Q100 Grade 1 Qualified VIN Range from 4.5V to 75V High-Side Adjustable Current Sense 2-, 1-A Peak MOSFET Gate Driver Input Undervoltage and Output Overvoltage Protection PWM and Analog Dimming Cycle-by-Cycle Current Limit Programmable Softstart and Slope Compensation Programmable, Synchronizable Switching Frequency Programmable Thermal Foldback Precision Voltage Reference Low Power Shutdown and Thermal Shutdown 2 Applications * * * * * LED Drivers - Buck, Boost, Buck-Boost, and SEPIC Indoor and Outdoor Area SSL Automotive General Illumination Constant-Current Regulators Adjustable high-side current sense allows for tight regulation of the LED current with the highest efficiency possible. The LM3424 uses standard peak current-mode control providing inherent input voltage feed-forward compensation for better noise immunity. It is designed to provide accurate thermal foldback with a programmable foldback breakpoint and slope. In addition, a 2.45V reference is provided. The LM3424 includes a high-voltage startup regulator that operates over a wide input range of 4.5 V to 75 V. The internal PWM controller is designed for adjustable switching frequencies of up to 2.0 MHz and external synchronization is possible. The controller is capable of high speed PWM dimming and analog dimming. Device Information(1) PART NUMBER LM3424 Typical Boost Application Circuit 2 3 4 5 PWM 6 7 8 TEMP 9 VIN LM3424 HSP HSN EN COMP SLOPE CSH IS RT/SYNC VCC GATE nDIM GND SS TGAIN DDRV OVP TSENSE HTSSOP (20) BODY SIZE (NOM) 6.50 mm x 4.40 mm (1) For all available packages, see the orderable addendum at the end of the datasheet. VIN 1 LM3424-Q1 PACKAGE 20 19 18 17 16 ILED 15 14 13 12 DAP 10 TREF VS 11 1 An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications, intellectual property matters and other important disclaimers. PRODUCTION DATA. LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com Table of Contents 1 2 3 4 5 6 7 Features .................................................................. Applications ........................................................... Description ............................................................. Revision History..................................................... Pin Configuration and Functions ......................... Specifications......................................................... 1 1 1 2 3 4 6.1 6.2 6.3 6.4 6.5 6.6 6.7 4 4 4 4 5 6 8 Absolute Maximum Ratings ...................................... ESD Ratings--LM3424 ............................................. ESD Ratings--LM3424-Q1 ....................................... Recommended Operating Conditions....................... Thermal Information .................................................. Electrical Characteristics........................................... Typical Characteristics ............................................. Detailed Description ............................................ 11 7.1 Overview ................................................................. 11 7.2 Functional Block Diagram ....................................... 11 7.3 Feature Description................................................. 12 7.4 Device Functional Modes........................................ 25 8 Application and Implementation ........................ 26 8.1 Application Information............................................ 26 8.2 Typical Applications ................................................ 29 9 Power Supply Recommendations...................... 61 9.1 Input Supply Current Limit ...................................... 61 10 Layout................................................................... 61 10.1 Layout Guidelines ................................................. 61 10.2 Layout Example .................................................... 62 11 Device and Documentation Support ................. 63 11.1 11.2 11.3 11.4 11.5 11.6 Device Support...................................................... Related Links ........................................................ Community Resources.......................................... Trademarks ........................................................... Electrostatic Discharge Caution ............................ Glossary ................................................................ 63 63 63 63 63 63 12 Mechanical, Packaging, and Orderable Information ........................................................... 63 4 Revision History NOTE: Page numbers for previous revisions may differ from page numbers in the current version. Changes from Revision B (October 2009) to Revision C Page * Adjusted temperature range in Features section. .................................................................................................................. 1 * Added Pin Configuration and Functions section, ESD Ratings table, Feature Description section, Device Functional Modes, Application and Implementation section, Power Supply Recommendations section, Layout section, Device and Documentation Support section, and Mechanical, Packaging, and Orderable Information section .............................. 1 * Changed "Operating Temperature Range (TJ = -40C to +125C)" to "Operating Temperature Range (TA = TJ = -40C to +125C)" in Electrical Characterization table Condition statement ........................................................................ 6 2 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 5 Pin Configuration and Functions PWP Package 20-Pin HTSSOP With PowerPADTM Top View VIN 1 20 HSP EN 2 19 HSN COMP 3 18 SLOPE CSH 4 RT 5 nDIM 6 17 IS 21 16 VCC DAP 15 GATE SS 7 14 GND TGAIN 8 13 DDRV 12 OVP TSENSE 9 11 VS TREF 10 Pin Functions PIN I/O DESCRIPTION NO. NAME 1 VIN I Input Voltage Bypass with 100 nF capacitor to GND as close to the device as possible. 2 EN I Enable Connect to > 2.4V to enable the device or to < 0.8V for low power shutdown. 3 COMP I Compensation Connect a capacitor to GND to compensate control loop. 4 CSH I Current Sense High Connect a resistor to GND to set the signal current. Can also be used to analog dim as explained in the Thermal Foldback and Analog Dimming section. 5 RT I Resistor Timing Connect a resistor to GND to set the switching frequency. Can also be used to synchronize to an external clock as explained in the Switching Frequency section. 6 nDIM I Dimming Input / Under-Voltage Protection Connect a PWM signal for dimming as detailed in the PWM Dimming section and/or a resistor divider from VIN to program input under-voltage lockout. 7 SS I Soft-start Connect a capacitor to GND to extend start-up time. 8 TGAIN I Temp Foldback Gain Connect a resistor to GND to set the foldback slope. 9 TSENSE I Temp Sense Input Connect a resistor/ thermistor divider from VS to sense the temperature as explained in the Thermal Foldback and Analog Dimming section. 10 TREF I Temp Foldback Reference Connect a resistor divider from VS to set the foldback reference voltage. 11 VS O Voltage Reference 2.45V reference for temperature foldback circuit and other external circuitry. 12 OVP I Over-Voltage Protection Connect a resistor divider from VO to program output over-voltage lockout. 13 DDRV O Dimming Gate Drive Output Connect to gate of dimming MOSFET. 14 GND 15 GATE O Main Gate Drive Output Connect to gate of main switching MOSFET. 16 VCC O Internal Regulator Output Bypass with a 2.2 F - 3.3 F ceramic capacitor to GND. 17 IS I Main Switch Current Sense Connect to the drain of the main N-channel MOSFET switch for RDS-ON sensing or to a sense resistor installed in the source of the same device. 18 SLOPE I Slope Compensation Connect a resistor to GND to set slope of additional ramp. 19 HSN I LED Current Sense Negative Connect through a series resistor to LED current sense resistor (negative). 20 HSP I LED Current Sense Positive Connect through a series resistor to LED current sense resistor (positive). DAP DAP GND Ground Connect to DAP to provide proper system GND GND Thermal pad on bottom of IC Connect to GND. Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 3 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com 6 Specifications 6.1 Absolute Maximum Ratings over operating free-air temperature range (unless otherwise noted) (1) (2) MIN MAX VIN, EN, nDIM -0.3 76 OVP, HSP, HSN -0.3 76 -0.3 IS Voltage 76 -2 for 100 ns VCC -0.3 8 VS, TREF, TSENSE, TGAIN, COMP, CSH, RT, SLOPE, SS -0.3 6 GATE, DDRV GND -0.3 VCC VCC + 2.5 for 100 ns -0.3 0.3 -2.5 for 100 ns 2.5 for 100 ns -1 OVP, HSP, HSN IS mA -30 30 A -1 1 mA Maximum Junction Temperature Internally Limited Maximum lead temperature (Reflow and Solder) (3) Storage temperature (3) A -1 GATE, DDRV Internally Limited (2) mA -100 SS Continuous power dissipation (1) V -2.5 for 100 ns VIN, EN, nDIM Continuous current UNIT -65 C 260 C 150 C Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability. If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and specifications. Refer toTI's packaging website for more detailed information and mounting techniques. http://www.ti.com/analogpackaging 6.2 ESD Ratings--LM3424 VALUE V(ESD) (1) (2) Electrostatic discharge Human body model (HBM), per ANSI/ESDA/JEDEC JS-001, all pins (1) 2500 Charged device model (CDM), per JEDEC specification JESD22-C101, all pins (2) 1000 UNIT V JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process. JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process. 6.3 ESD Ratings--LM3424-Q1 VALUE V(ESD) (1) Electrostatic discharge Human-body model (HBM), per AEC Q100-002 (1) 2500 Charged-device model (CDM), per AEC Q100-011 1000 UNIT V AEC Q100-002 indicates that HBM stressing shall be in accordance with the ANSI/ESDA/JEDEC JS-001 specification. 6.4 Recommended Operating Conditions MIN MAX UNIT Operating Ambient Temperature Range -40 125 C Input Voltage VIN 4.5 75 V 4 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 6.5 Thermal Information LM3424, LM3424-Q1 THERMAL METRIC (1) PWP (HTSSOP) UNIT 20 PINS RJA Junction-to-ambient thermal resistance 36.7 C/W RJC(top) Junction-to-case (top) thermal resistance 21.5 C/W RJB Junction-to-board thermal resistance 18 C/W JT Junction-to-top characterization parameter 0.5 C/W JB Junction-to-board characterization parameter 17.8 C/W RJC(bot) Junction-to-case (bottom) thermal resistance 1.9 C/W (1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application report, SPRA953. Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 5 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com 6.6 Electrical Characteristics MIN and MAX limits apply over the full Operating Temperature Range (TA = TJ = -40C to 125C) unless otherwise specified. Minimum and Maximum limits are ensured through test, design, or statistical correlation. Unless otherwise stated the following condition applies: TJ = 25C, VIN = 14 V. PARAMETER TEST CONDITIONS MIN (1) TYP (2) MAX (1) 7.35 UNIT STARTUP REGULATOR (VCC) VCC-REG VCC Regulation ICC = 0 mA 6.3 6.9 ICC-LIM VCC Current Limit VCC = 0 V 20 25 IQ Quiescent Current EN = 3 V, Static ISD Shutdown Current EN = 0 V, MAX: TJ = 25C VCC-UVLO VCC UVLO Threshold VCC Increasing VCC Decreasing VCC-HYS 3.7 VCC UVLO Hysteresis V mA 2 3 mA 0.1 1 A 4.17 4.50 V 4.08 V 0.1 V ENABLE (EN) VEN-ST EN Startup Threshold EN Increasing 1.75 EN decreasing VEN-HYS EN Startup Hysteresis REN EN Pull-down Resistance 0.8 2.4 V 1.63 V 0.1 V 0.45 0.82 1.30 M 1.185 1.24 1.285 V 13 20 27 A OVER-VOLTAGE PROTECTION (OVP) VTH-OVP OVP OVLO Threshold OVP Increasing IHYS-OVP OVP Hysteresis Source Current OVP Active (high) CSH Reference Voltage With Respect to GND 1.21 1.235 1.26 V Error Amplifier Input Bias Current MIN, MAX: TJ = 25C -0.6 0 0.6 A 26 35 ERROR AMPLIFIER VCSH COMP Sink / Source Current 17 Transconductance See (3) Linear Input Range (3) A 100 A/V 125 mV 1 MHz Transconductance Bandwidth -6-dB Unloaded Response fSW Switching Frequency RT = 36 k 164 207 250 kHz RT = 12 k 525 597 669 kHz VRT-SYNC Sync Threshold OSCILLATOR (RT) 3.5 V PWM COMPARATOR VCP-BASE COMP to PWM Offset - No Slope Compensation 750 900 1050 mV SLOPE COMPENSATION (SLOPE) VCP Slope Compensation Amplitude Additional COMP to PWM Offset - SLOPE sinking 100 A 85 mV CURRENT LIMIT (IS) VLIM Current Limit Threshold 215 VLIM Delay to Output tON-MIN Leading Edge Blanking Time 140 245 275 mV 35 75 ns 240 340 ns HIGH SIDE TRANSCONDUCTANCE AMPLIFIER Input Bias Current 10 Transconductance (1) (2) (3) 6 A 20 mA/V Input Offset Current -1.5 0 1.5 A Input Offset Voltage -5 0 5 mV All limits ensured at room temperature (standard typeface) and at temperature extremes (bold typeface). All room temperature limits are 100% production tested. All limits at temperature extremes are ensured via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL). Typical numbers are at 25C and represent the most likely norm. These electrical parameters are ensured by design, and are not verified by test. Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 Electrical Characteristics (continued) MIN and MAX limits apply over the full Operating Temperature Range (TA = TJ = -40C to 125C) unless otherwise specified. Minimum and Maximum limits are ensured through test, design, or statistical correlation. Unless otherwise stated the following condition applies: TJ = 25C, VIN = 14 V. PARAMETER TEST CONDITIONS Transconductance Bandwidth ICSH = 100 A MIN (1) (3) TYP (2) MAX (1) 500 UNIT kHz GATE DRIVER (GATE) RSRC-GATE GATE Sourcing Resistance GATE = High 2 6 RSNK-GATE GATE Sinking Resistance GATE = Low 1.3 4.5 UNDERVOLTAGE LOCKOUT and DIM INPUT (nDIM) VTH-nDIM nDIM / UVLO Threshold 1.185 1.240 1.285 V IHYS-nDIM nDIM Hysteresis Current 13 20 27 A DIM DRIVER (DDRV) RSRC-DDRV DDRV Sourcing Resistance DDRV = High 13.5 30 RSNK-DDRV DDRV Sinking Resistance DDRV = Low 3.5 10 nDIM rising to DDRV rising 700 ns nDIM falling to DDRV falling 360 ns 10 A SOFT-START (SS) ISS Soft-start current THERMAL CONTROL VS VS Voltage IVS = 0A 2.4 IVS = 1 mA 2.45 2.5 V TREF input bias current VTREF = 1.5 V VTSENSE = 1.5 V 0.1 A TSENSE Input Bias Current VTREF = 1.5 V VTSENSE = 1.5 V 0.1 A 600 A VTREF = 1.5 V VTSENSE = 0.5 V 100 A VTREF = 1.5 V VTSENSE = 1.4 V 10 A VTREF = 1.5 V VTSENSE = 1.5 V 2 A ITGAIN-MAX TGAIN Maximum Sourcing Current VTGAIN = 2 V ITF CSH Current with High-side Amplifier Disabled RTGAIN = 10 k 200 THERMAL SHUTDOWN TSD Thermal Shutdown Threshold See (3) 165 C THYS Thermal Shutdown Hysteresis See (3) 25 C Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 7 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com 6.7 Typical Characteristics TA=25C and VIN = 14 V unless otherwise specified. The measurements for Figure 1, Figure 3, andFigure 6 were made using the standard boost evaluation board from AN-1969 (SNVA397). The measurements for Figure 2, Figure 4, and Figure 5 were made using the standard buck-boost evaluation board from AN-1967 (SNVA398). 100 100 95 EFFICIENCY (%) EFFICIENCY (%) 95 90 90 85 80 85 75 80 10 15 20 25 70 30 0 16 32 Figure 1. Boost Efficiency vs Input Voltage 80 Figure 2. Buck-Boost Efficiency vs. Input Voltage 1.010 1.02 1.005 1.01 ILED (A) ILED (A) 64 VO = 21 V (6 LEDs) VO = 32 V (9 LEDs) 1.000 0.995 1.00 0.99 0.990 0.98 5 10 15 20 VIN (V) 25 30 0 16 32 48 64 80 VIN (V) VO = 32 V (9 LEDs) VO = 21 V (6 LEDs) Figure 3. Boost LED Current vs. Input Voltage Figure 4. Buck-Boost LED Current vs. Input Voltage 1.0 1.0 0.8 0.8 0.6 0.6 ILED (A) ILED (A) 48 VIN (V) VIN (V) 0.4 1 kHz 0.4 25 kHz 0.2 0.2 0.0 0 20 40 60 80 0.8 100 ICSH (eA) VIN = 24 V 40 60 80 VO = 32V (9 LEDs) Figure 5. Analog Dimming Submit Documentation Feedback 20 100 DUTY CYCLE (%) VO = 21 V (6 LEDs) 8 0 VIN = 24 V Figure 6. PWM Dimming Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 Typical Characteristics (continued) TA=25C and VIN = 14 V unless otherwise specified. The measurements for Figure 1, Figure 3, andFigure 6 were made using the standard boost evaluation board from AN-1969 (SNVA397). The measurements for Figure 2, Figure 4, and Figure 5 were made using the standard buck-boost evaluation board from AN-1967 (SNVA398). 7.20 1.250 1.245 7.10 VCC (V) VCSH (V) 1.240 1.235 7.00 6.90 1.230 6.80 1.225 1.220 -50 -14 22 58 94 6.70 -50 130 -14 22 58 94 130 TEMPERATURE (C) TEMPERATURE (C) Figure 8. VCC vs. Junction Temperature Figure 7. VCSH vs. Junction Temperature 248 2.500 VLIM (mV) VS (V) 246 2.450 244 242 2.400 -50 -14 22 58 94 240 -50 130 -14 TEMPERATURE (C) Figure 9. VS vs. Junction Temperature 58 94 130 Figure 10. VLIM vs. Junction Temperature 1000 255 RT = 12 kO 250 245 fSW (kHz) tON-MIN (ns) 22 TEMPERATURE (C) 240 RT = 36 kO 235 230 100 225 -50 -14 22 58 94 130 -50 22 58 94 130 TEMPERATURE (C) TEMPERATURE (C) Figure 11. Minimum On-Time vs. Junction Temperature -14 Figure 12. Switching Frequency vs. Junction Temperature Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 9 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com Typical Characteristics (continued) TA=25C and VIN = 14 V unless otherwise specified. The measurements for Figure 1, Figure 3, andFigure 6 were made using the standard boost evaluation board from AN-1969 (SNVA397). The measurements for Figure 2, Figure 4, and Figure 5 were made using the standard buck-boost evaluation board from AN-1967 (SNVA398). 1M 100.3 100.1 RT (O) ITF (eA) 100k 99.9 10k 99.7 99.5 -50 -14 22 58 94 1k 10k 130 100k TEMPERATURE (C) RGAIN = 10 k VTSENSE = 0.5 V VTREF = 1.5 V 1.25 1.00 1.00 0.75 0.75 RGAIN = 15 k: 0.50 RBIAS = 84.5 k: 0.25 RGAIN = 10 k: 0.00 0 25 RBIAS = 24.3 k: 0.50 RGAIN = 5 k: 0.25 50 75 100 125 RBIAS = 43.2 k: 0.00 0 25 TEMPERATURE (C) RREF1 = RREF2 = 49.9 k RNTC-BK = RBIAS = 43.2 k Submit Documentation Feedback 50 75 100 125 TEMPERATURE (C) RREF1 = RREF2 = 49.9 k Figure 15. Ideal Thermal Foldback with Varied Slope 10 10M Figure 14. Switching Frequency vs. Timing Resistance 1.25 ILED (A) ILED (A) Figure 13. ITF vs. Junction Temperature 1M fSW (Hz) RGAIN = 10 k Figure 16. Ideal Thermal Foldback with Varied Breakpoint Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 7 Detailed Description 7.1 Overview The LM3424 is an N-channel MOSFET (NFET) controller for buck, boost and buck-boost current regulators which are ideal for driving LED loads. The controller has wide input voltage range allowing for regulation of a variety of LED loads. The high-side differential current sense, with low adjustable threshold voltage, provides an excellent method for regulating output current while maintaining high system efficiency. The LM3424 uses peak current mode control providing good noise immunity and an inherent cycle-by-cycle current limit. The adjustable current sense threshold provides the capability to amplitude (analog) dim the LED current and the thermal foldback circuitry allows for precise temperature management of the LEDs. The output enable/disable function coupled with an internal dimming drive circuit provides high speed PWM dimming through the use of an external MOSFET placed at the LED load. When designing, the maximum attainable LED current is not internally limited because the LM3424 is a controller. Instead it is a function of the system operating point, component choices, and switching frequency allowing the LM3424 to easily provide constant currents up to 5A. This simple controller contains all the features necessary to implement a high efficiency versatile LED driver. 7.2 Functional Block Diagram VIN 6.9V LDO Regulator EN VCC 820k UVLO (4.1V) VCC UVLO UVLO HYSTERESIS 1.24V Standby 20 PA nDIM REFERENCE TLIM Thermal VCC Limit Dimming 1.24V DDRV OVLO Reset Dominant Clock RT Artificial Ramp Oscillator VCC Q S GATE SLOPE R LEB GND W = 240 ns COMP 20 PA 1.24V PWM OVP HYSTERESIS CSH OVP OVLO HSP 90k 1.24V 10 PA HSN 1.7k 1.24V CURRENT LIMIT IS 0.245V 100k 100k VS LEB 100k 10 PA 100k TREF COMP SS TSENSE 100k STANDBY 100k TGAIN Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 11 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com 7.3 Feature Description 7.3.1 Current Regulators iL (t) IL-MAX AiL-PP IL IL-MIN tON = DTS tOFF = (1-D)TS t 0 TS Figure 17. Ideal CCM Regulator Inductor Current iL(t) Current regulators can be designed to accomplish three basic functions: buck, boost, and buck-boost. All three topologies in their most basic form contain a main switching MOSFET, a recirculating diode, an inductor and capacitors. The LM3424 is designed to drive a ground referenced NFET which is perfect for a standard boost regulator. Buck and buck-boost regulators, on the other hand, usually have a high-side switch. When driving an LED load, a ground referenced load is often not necessary, therefore a ground referenced switch can be used to drive a floating load instead. The LM3424 can then be used to drive all three basic topologies as shown in the Basic Topology Schematics section. Other topologies such as the SEPIC and flyback converter (both derivatives of the buck-boost) can be implemented as well. Looking at the buck-boost design, the basic operation of a current regulator can be analyzed. During the time that the NFET (Q1) is turned on (tON), the input voltage source stores energy in the inductor (L1) while the output capacitor (CO) provides energy to the LED load. When Q1 is turned off (tOFF), the re-circulating diode (D1) becomes forward biased and L1 provides energy to both CO and the LED load. Figure 17 shows the inductor current (iL(t)) waveform for a regulator operating in CCM. The average output LED current (ILED) is proportional to the average inductor current (IL) , therefore if IL is tightly controlled, ILED will be well regulated. As the system changes input voltage or output voltage, the ideal duty cycle (D) is varied to regulate IL and ultimately ILED. For any current regulator, D is a function of the conversion ratio: Buck D= VO VIN (1) VO - VIN VO (2) Boost D= Buck-Boost D= VO VO + VIN (3) 7.3.2 Peak Current Mode Control Peak current mode control is used by the LM3424 to regulate the average LED current through an array of HBLEDs. This method of control uses a series resistor in the LED path to sense LED current and can use either a series resistor in the MOSFET path or the MOSFET RDS-ON for both cycle-by-cycle current limit and input voltage feed forward. The controller has a fixed switching frequency set by an internal programmable oscillator which means current mode instability can occur at duty cycles higher than 50%. To mitigate this standard problem, an artificial ramp is added to the control signal internally. The slope of this ramp is programmable to allow for a wider range of component choices for a given design. A detailed explanation of this control method is presented in the following sections. 12 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 Feature Description (continued) 7.3.3 Average LED Current To first understand how the LM3424 regulates LED current, the thermal foldback functionality will be ignored. Figure 18 shows the physical implementation of the LED current sense circuitry assuming the thermal foldback circuitry is a simple current source which, for now, will be set to zero (ITF = 0A). The LM3424 uses an external current sense resistor (RSNS) placed in series with the LED load to convert the LED current (ILED) into a voltage (VSNS). The HSP and HSN pins are the inputs to the high-side sense amplifier which are forced to be equal potential (VHSP=VHSN) through negative feedback. Because of this, the VSNS voltage is forced across RHSP which generates a current that is summed with the thermal foldback current (ITF) to generate the signal current (ICSH) which flows out of the CSH pin and through the RCSH resistor. The error amplifier will regulate the CSH pin to 1.24V and assuming ITF = 0A, ICSH can be calculated: VSNS ICSH = RHSP (4) This means VSNS will be regulated as follows: RHSP VSNS = 1.24V x RCSH (5) ILED can then be calculated: VSNS 1.24V RHSP x ILED = = RSNS RSNS RCSH (6) The selection of the three resistors (RSNS, RCSH, and RHSP) is not arbitrary. For matching and noise performance, the suggested signal current ICSH is approximately 100 A. This current does not flow in the LEDs and will not affect either the off-state LED current or the regulated LED current. ICSH can be above or below this value, but the high-side amplifier offset characteristics may be affected slightly. In addition, to minimize the effect of the high-side amplifier voltage offset on LED current accuracy, the minimum VSNS is suggested to be 50 mV. Finally, a resistor (RHSN = RHSP) should be placed in series with the HSN pin to cancel out the effects of the input bias current (~10 A) of both inputs of the high-side sense amplifier. Note that he CSH pin can also be used as a low-side current sense input regulated to 1.24V. The high-side sense amplifier is disabled if HSP and HSN are tied to GND. LM3424 ILED VSNS RSNS RHSP RHSN HSP High-Side Sense Amplifier Thermal Foldback Current HSN ITF RCSH CSH ICSH Error Amplifier 1.24V CCMP To PWM Comparator COMP Figure 18. LED Current Sense Circuitry 7.3.4 Thermal Foldback and Analog Dimming Thermal foldback is necessary in many applications due to the extreme temperatures created in LED environments. In general, two functions are necessary: a temperature breakpoint (TBK) after which the nominal operating current needs to be reduced, and a slope corresponding to the amount of LED current decrease per temperature increase as shown in Figure 19. The LM3424 allows the user to program both the breakpoint and slope of the thermal foldback profile. Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 13 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com Feature Description (continued) ILED v 1 RGAIN 0 TBK TEND T Figure 19. Ideal Thermal Foldback Profile LM3424 VS 2.45V ILED VSNS RSNS RHSP RHSN HSP High-Side Sense Amplifier RREF2 100k 100k 100k TGAIN ICSH RNTC Error Amplifier 1.24V CCMP RBIAS TSENSE 100k CSH RREF1 VDIF HSN ITF RCSH NTC TREF To PWM Comparator RGAIN COMP LM94022 Precision Temp Sensor Figure 20. Thermal Foldback Circuitry Foldback is accomplished by adding current (ITF) to the CSH summing node. As more current is added, less current is needed from the high side amplifier and correspondingly, the LED current is regulated to a lower value. The final temperature (TEND) is reached when ITF = ICSH causing no current to be needed from the high-side amplifier, yielding ILED = 0A. Figure 20 shows how the thermal foldback circuitry is physically implemented in the system. ITF is set by placing a differential voltage (VDIF = VTREF - VTSENSE) across TSENSE and TREF. VTREF can be set with a simple resistor divider (RREF1 and RREF2) supplied from the VS voltage reference (typical 2.45V). VTSENSE is set with a temperature dependant voltage (as temperature increases, voltage should decrease). An NTC thermistor is the most cost effective device used to sense temperature. As the temperature of the thermistor increases, its resistance decreases (albeit non-linearly). Usually, the NTC manufacturer's datasheet will detail the resistance-temperature characteristic of the thermistor. The thermistor will have a different resistance (RNTC) at each temperature. The nominal resistance of an NTC is the resistance when the temperature is 25C (R25) and in many datasheets this will be given a multiplier of 1. Then the resistance at a higher temperature will have a multiplier less than 1 (that is, R85 multiplier is 0.161 therefore R85 = 0.161 x R25). Given a desired TBK and TEND, the corresponding resistances at those temperatures (RNTC-BK and RNTC-END) can be found. Using the NTC method, a resistor divider from VS can be implemented with a resistor connected between VS and TSENSE and the NTC thermistor placed at the desired location and connected from TSENSE to GND. This will ensure that the desired temperature-voltage characteristic occurs at TSENSE. If a linear decrease over the foldback range is necessary, a precision temperature sensor such as the LM94022 can be used instead as shown in Figure 20. Either method can be used to set VTSENSE according to the temperature. However, for the rest of this datasheet, the NTC method will be used for thermal foldback calculations. 14 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 Feature Description (continued) During operation, if VDIF < 0V, then the sensed temperature is less than TBK and the differential sense amplifier will regulate its output to zero forcing ITF = 0. This maintains the nominal LED current and no foldback is observed. At TBK, VDIF = 0V exactly and ITF is still zero. Looking at the manufacturer's datasheet for the NTC thermistor, RNTC-BK can be obtained for the desired TBK and the voltage relationship at the breakpoint (VTSENSE-BK = VTREF) can be defined: RREF1 RNTC-BK = RREF1 + RREF2 RNTC-BK + RBIAS (7) A general rule of thumb is to set RREF1 = RREF2 simplifying the breakpoint relationship to RBIAS = RNTC-BK. If VDIF > 0V (temperature is above TBK), then the amplifier will regulate its output equal to the input forcing VDIF across the resistor (RGAIN) connected from TGAIN to GND. RGAIN ultimately sets the slope of the LED current decrease with respect to increasing temperature by changing ITF: VTREF - VTSENSE ITF = RGAIN (8) If an analog temperature sensor such as the LM94022 is used, then RBIAS and the NTC are not necessary and VTSENSE will be the direct voltage output of the sensor. Since the NTC is not usually local to the controller, a bypass capacitor (CNTC) is suggested from TSENSE to GND. If a capacitor is used at TSENSE, then a capacitor (CREF) of equal or greater value should be placed from TREF to GND in order to ensure the controller does not start-up in foldback. Alternatively, a smaller CREF can be used to create a fade-up function at start-up (see Application Information). Thermal foldback is simply analog dimming according to a specific profile, therefore any method of controlling the differential voltage between TREF and TSENSE can be use to analog dim the LED current. The corresponding LED current for any VDIF > 0V is defined: RHSP* (c) RSNS ILED = (ICSH - ITF) x (9) The CSH pin can also be used to analog dim the LED current by adjusting the current sense voltage (VSNS), similar to thermal foldback. There are several different methods to adjust VSNS using the CSH pin: 1. External variable resistance: Adjust a potentiometer placed in series with RCSH to vary VSNS. 2. External variable current source: Source current (0 A to ICSH) into the CSH pin to adjust VSNS. Variable Current Source LM3424 VS VCC Q8 Q7 RMAX Q6 RADJ RBIAS CSH RCSH RADJ Variable Resistance Figure 21. Analog Dimming Circuitry Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 15 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com Feature Description (continued) In general, analog dimming applications require a lower switching frequency to minimize the effect of the leading edge blanking circuit. As the LED current is reduced, the output voltage and the duty cycle decreases. Eventually, the minimum on-time is reached. The lower the switching frequency, the wider the linear dimming range. Figure 21 shows how both CSH methods are physically implemented. Method 1 uses an external potentiometer in the CSH path which is a simple addition to the existing circuitry. However, the LEDs cannot dim completely because there is always some resistance causing signal current to flow. This method is also susceptible to noise coupling at the CSH pin since the potentiometer increases the size of the signal current loop. Method 2 provides a complete dimming range and better noise performance, though it is more complex. Like thermal foldback, it simply sources current into the CSH pin, decreasing the amount of signal current that is necessary. This method consists of a PNP current mirror and a bias network consisting of an NPN, 2 resistors and a potentiometer (RADJ), where RADJ controls the amount of current sourced into the CSH pin. A higher resistance value will source more current into the CSH pin causing less regulated signal current through RHSP, effectively dimming the LEDs. Q7 and Q8 should be a dual pair PNP for best matching and performance. The additional current (IADD) sourced into the CSH pin can be calculated: IADD = RADJ x VREF * R + R - VBE-Q6 (c) ADJ MAX RBIAS (10) The corresponding ILED for a specific IADD is: RHSP* (c) RSNS ILED = (ICSH - IADD) x (11) 7.3.5 Current Sense and Current Limit The LM3424 achieves peak current mode control using a comparator that monitors the main MOSFET (Q1) transistor current, comparing it with the COMP pin voltage as shown in Figure 22. Further, it incorporates a cycle-by-cycle over-current protection function. Current limit is accomplished by a redundant internal current sense comparator. If the voltage at the current sense comparator input (IS) exceeds 245 mV (typical), the on cycle is immediately terminated. The IS input pin has an internal N-channel MOSFET which pulls it down at the conclusion of every cycle. The discharge device remains on an additional 240 ns (typical) after the beginning of a new cycle to blank the leading edge spike on the current sense signal. The leading edge blanking (LEB) determines the minimum achievable on-time (tON-MIN). RDS-ON Sensing Q1 LM3424 COMP GATE 0.9V RLIM Sensing PWM Ramp IS 0.245V IT RLIM LEB Ramp Ramp Generator SLOPE GND RSLP Figure 22. Current Sense / Current Limit Circuitry 16 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 Feature Description (continued) There are two possible methods to sense the transistor current. The RDS-ON of the main power MOSFET can be used as the current sense resistance because the IS pin was designed to withstand the high voltages present on the drain when the MOSFET is in the off state. Alternatively, a sense resistor located in the source of the MOSFET may be used for current sensing, however a low inductance (ESL) type is suggested. The cycle-bycycle current limit (ILIM) can be calculated using either method as the limiting resistance (RLIM): 245 mV ILIM = RLIM (12) In general, the external series resistor allows for more design flexibility, however it is important to ensure all of the noise sensitive low power ground connections are connected together local to the controller and a single connection is made to GND. 7.3.6 Slope Compensation The LM3424 has programmable slope compensation in order to provide stability over a wide range of operating conditions. Without slope compensation, a well-known condition called current mode instability (or sub-harmonic oscillation) can result if there is a perturbation of the MOSFET current sense voltage at the IS pin, due to noise or a some type of transient. Through a mathematical / geometrical analysis of the inductor current (IL) and the corresponding control current (IC, it can be shown that if D < 0.5, the effect of the perturbation will decrease each switching cycle and the system will remain stable. However, if D > 0.5 then the perturbation will grow as shown in Figure 23, eventually causing a "period doubling" effect where the effect of the perturbation remains, yielding current mode instability. Looking at Figure 22, the positive PWM comparator input is the IS voltage, a mirror of IL during tON, plus a typical 900 mV offset. The negative input of the PWM comparator is the COMP pin which is proportional to IC, the threshold at which the main MOSFET (Q1) is turned off. The LM3424 mitigates current mode instability by implementing an aritifical ramp (commonly called slope compensation) which is summed with the sensed MOSFET current at the IS pin as shown in Figure 22. This combined signal is compared to the COMP pin to generate the PWM signal. An increase in the ramp that is added to the sense voltage will increase the maximum achievable duty cycle. It should be noted that as the artificial ramp is increased more and more, the control method approaches standard voltage mode control and the benefits of current mode control are reduced. To program the slope compensation, an external resistor, RSLP, is connected from SLOPE to GND. This sets the slope of the artificial ramp that is added to the MOSFET current sense voltage. A smaller RSLP value will increase the slope of the added ramp. A simple calculation is suggested to ensure any duty cycle is attainable while preventing the addition of excessive ramp. This method requires the artifical ramp slope (MA) to be equal to half the inductor slope during tOFF: 12 VO 7.5 x 10 MA = = R T x R SLP x RLIM 2 x L1 (13) iL (t) IC Ideal iL (t) Actual iL (t) TS 2TS t 0 Figure 23. "Period Doubling" due to Current Mode Instability Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 17 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com Feature Description (continued) 7.3.7 Control Loop Compensation The LM3424 control loop is modeled like any current mode controller. Using a first order approximation, the uncompensated loop can be modeled as a single pole created by the output capacitor and, in the boost and buck-boost topologies, a right half plane zero created by the inductor, where both have a dependence on the LED string dynamic resistance. There is also a high frequency pole in the model, however it is near the switching frequency and plays no part in the compensation design process therefore it will be neglected. Since ceramic capacitance is recommended for use with LED drivers due to long lifetimes and high ripple current rating, the ESR of the output capacitor can also be neglected in the loop analysis. Finally, there is a DC gain of the uncompensated loop which is dependent on internal controller gains and the external sensing network. A buck-boost regulator will be used as an example case. See the Application Information section for compensation of all topologies. The uncompensated loop gain for a buck-boost regulator is given by the following equation: s * 1 ZZ1 (c) TU = TU0 x s * 1+ ZP1 (c) (14) Where the uncompensated DC loop gain of the system is described as: Dc x 500V x RCSH x RSNS Dc x 620V TU0 = = (1+ D) x RHSP x R LIM (1+ D) x ILED x R LIM (15) And the output pole (P1) is approximated: 3 1+ D ZP1 = rD x CO (16) And the right half plane zero (Z1) is: rD x Dc2 ZZ1 = D x L1 (17) 100 oZ1 80 135 oP1 90 GAIN GAIN (dB) 0 40 PHASE -45 20 0 Phase Margin -90 0 -20 -135 -40 -180 -60 1e-1 PHASE () 45 60 1e1 1e3 1e5 -225 1e7 FREQUENCY (Hz) Figure 24. Uncompensated Loop Gain Frequency Response 18 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 Feature Description (continued) Figure 24 shows the uncompensated loop gain in a worst-case scenario when the RHP zero is below the output pole. This occurs at high duty cycles when the regulator is trying to boost the output voltage significantly. The RHP zero adds 20dB/decade of gain while loosing 45/decade of phase which places the crossover frequency (when the gain is zero dB) extremely high because the gain only starts falling again due to the high frequency pole (not modeled or shown in figure). The phase will be below -180 at the crossover frequency which means there is no phase margin (180 + phase at crossover frequency) causing system instability. Even if the output pole is below the RHP zero, the phase will still reach -180 before the crossover frequency in most cases yielding instability. LM3424 ILED RHSP HSP High-Side Sense Amplifier CFS VSNS RSNS RHSN Thermal Foldback Current HSN RFS sets oP3 RCSH Error Amplifier CSH 1.24V sets oP2 CCMP RO To PWM Comparator COMP Figure 25. Compensation Circuitry To mitigate this problem, a compensator should be designed to give adequate phase margin (above 45) at the crossover frequency. A simple compensator using a single capacitor at the COMP pin (CCMP) will add a dominant pole to the system, which will ensure adequate phase margin if placed low enough. At high duty cycles (as shown in Figure 24), the RHP zero places extreme limits on the achievable bandwidth with this type of compensation. However, because an LED driver is essentially free of output transients (except catastrophic failures open or short), the dominant pole approach, even with reduced bandwidth, is usually the best approach. The dominant compensation pole (P2) is determined by CCMP and the output resistance (RO) of the error amplifier (typically 5 M): 1 P2 = 5 x 106 x CCMP (18) It may also be necessary to add one final pole at least one decade above the crossover frequency to attenuate switching noise and, in some cases, provide better gain margin. This pole can be placed across RSNS to filter the ESL of the sense resistor at the same time. Figure 25 shows how the compensation is physically implemented in the system. The high frequency pole (P3) can be calculated: 1 ZP3 = RFS x CFS (19) The total system transfer function becomes: s * 1 ZZ1 (c) T = TU0 x * s s * s * 1+ ZP1 x 1+ ZP2 x 1+ ZP3 (c) (c) (c) (20) The resulting compensated loop gain frequency response shown in Figure 26 indicates that the system has adequate phase margin (above 45) if the dominant compensation pole is placed low enough, ensuring stability: Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 19 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com Feature Description (continued) 90 80 oP2 45 60 0 GAIN 20 0 oZ1 -90 PHASE oP3 -20 60 Phase Margin -40 -45 oP1 PHASE () GAIN (dB) 40 -135 -180 -225 -60 -80 1e-1 1e1 1e3 1e5 -270 1e7 FREQUENCY (Hz) Figure 26. Compensated Loop Gain Frequency Response 7.3.8 Start-Up Regulator and Soft-Start The LM3424 includes a high voltage, low dropout bias regulator. When power is applied, the regulator is enabled and sources current into an external capacitor (CBYP) connected to the VCC pin. The recommended bypass capacitance for the VCC regulator is 2.2 F to 3.3 F. The output of the VCC regulator is monitored by an internal UVLO circuit that protects the device from attempting to operate with insufficient supply voltage and the supply is also internally current limited. The LM3424 also has programmable soft-start, set by an external capacitor (CSS), connected from SS to GND. For CSS to affect start-up, CREF > CNTC must be maintained so that the converter does not start in foldback mode. Figure 27 shows the typical start-up waveforms for the LM3424 assuming CREF > CNTC. VCMP 0.9V 0 tVCC tCMP tCO 0.9V 0.7V 0 tVCC tCMP-SS tSS tCO t Figure 27. Start-up Waveforms First, CBYP is charged to be above VCC UVLO threshold (~4.2V). The CVCC charging time (tVCC) can be estimated as: 4.2V t VCC = x CBYP = 168: x CBYP 25 mA (21) Assuming there is no CSS or if CSS is less than 40% of CCMP , CCMP is then charged to 0.9V over the charging time (tCMP) which can be estimated as: t CMP = 20 0.9V x CCMP = 36 k: x CCMP 25 PA Submit Documentation Feedback (22) Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 Feature Description (continued) Once CCMP = 0.9V, the part starts switching to charge CO until the LED current is in regulation. The CO charging time (tCO) can be roughly estimated as: V t CO = CO x O ILED (23) If CSS is greater than 40% of CCMP, the compensation capacitor will only charge to 0.7V over a smaller CCMP charging time (tCMP-SS) which can be estimated as: 0.70V t CMP - SS = x CCMP = 28 k: x CCMP 25 PA (24) Then COMP will clamp to SS, forcing COMP to rise (the last 200 mV before switching begins) according to the CSS charging time (tSS) which can be estimated as: 0. 2V t SS = x CSS = 20 k: x CSS 10 PA (25) The system start-up time (tSU or tSU-SS) is defined as: CSS < 0.4 x CCMP t SU = t VCC + t CMP + t CO (26) CSS > 0.4 x CCMP t SU - SS = t VCC + t CMP- SS + t SS + t CO (27) As a general rule of thumb, standard smooth startup operation can be achieved with CSS = CCMP. 7.3.9 Overvoltage Lockout (OVLO) The LM3424 can be configured to detect an output (or input) over-voltage condition via the OVP pin. The pin features a precision 1.24V threshold with 20 A (typical) of hysteresis current as shown in Figure 28. When the OVLO threshold is exceeded, the GATE pin is immediately pulled low and a 20 A current source provides hysteresis to the lower threshold of the OVLO hysteretic band. If the LEDs are referenced to a potential other than ground (floating), as in the buck-boost and buck configuration, the output voltage (VO) should be sensed and translated to ground by using a single PNP as shown in Figure 29. The over-voltage turn-off threshold (VTURN-OFF) is defined: Ground Referenced R + ROV 2* VTURN - OFF = 1.24V x OV1 (c) R OV1 (28) Floating 0.5 x R OV1+ R OV2* VTURN - OFF = 1.24V x R OV1 (c) (29) In the ground referenced configuration, the voltage across ROV2 is VO - 1.24 V whereas in the floating configuration it is VO - 620 mV where 620 mV approximates VBE of the PNP. The over-voltage hysteresis (VHYSO) is defined: VHYSO = 20 PA x ROV2 Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 (30) Submit Documentation Feedback 21 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com Feature Description (continued) LM3424 VO 20 PA ROV2 OVP OVLO 1.24V ROV1 Figure 28. Over-Voltage Protection Circuitry LED+ ROV2 LM3424 LEDOVP ROV1 Figure 29. Floating Output OVP Circuitry 7.3.10 Input Undervoltage Lockout (UVLO) The nDIM pin is a dual-function input that features an accurate 1.24V threshold with programmable hysteresis as shown in Figure 30. This pin functions as both the PWM dimming input for the LEDs and as a VIN UVLO. When the pin voltage rises and exceeds the 1.24V threshold, 20 A (typical) of current is driven out of the nDIM pin into the resistor divider providing programmable hysteresis. LM3424 VIN 20 PA RUV2 RUV1 nDIM 1.24V RUVH UVLO (optional) Figure 30. UVLO Circuit When using the nDIM pin for UVLO and PWM dimming concurrently, the UVLO circuit can have an extra series resistor to set the hysteresis. This allows the standard resistor divider to have smaller resistor values minimizing PWM delays due to a pull-down MOSFET at the nDIM pin (see PWM Dimming section). In general, at least 3V of hysteresis is preferable when PWM dimming, if operating near the UVLO threshold. The turn-on threshold (VTURN-ON) is defined as follows: R UV1 + RUV2* VTURN ON - = 1. 24V x (c) RUV1 22 Submit Documentation Feedback (31) Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 Feature Description (continued) The hysteresis (VHYS) is defined as follows: 7.3.10.1 UVLO Only VHYS = 20 PA x RUV2 (32) 7.3.10.2 PWM Dimming and UVLO R x (RUV1 + RUV2) * VHYS = 20 PA x RUV2 + UVH RUV1 (c) (33) 7.3.11 PWM Dimming The active low nDIM pin can be driven with a PWM signal which controls the main NFET and the dimming FET (dimFET). The brightness of the LEDs can be varied by modulating the duty cycle of this signal. LED brightness is approximately proportional to the PWM signal duty cycle, (that is, 30% duty cycle at approximately 30% LED brightness). This function can be ignored if PWM dimming is not required by using nDIM solely as a VIN UVLO input as described in the Input Undervoltage Lockout (UVLO) section or by tying it directly to VCC or VIN. Inverted PWM VIN LM3424 DDIM RUV2 nDIM RUVH RUV1 QDIM Standard PWM Figure 31. PWM Dimming Circuit Figure 31 shows how the PWM signal is applied to nDIM: 1. Connect the dimming MOSFET (QDIM) with the drain to the nDIM pin and the source to GND. Apply an external logic-level PWM signal to the gate of QDIM. 2. Connect the anode of a Schottky diode (DDIM) to the nDIM pin. Apply an inverted external logic-level PWM signal to the cathode of the same diode. The DDRV pin is a PWM output that follows the nDIM PWM input signal. When the nDIM pin rises, the DDRV pin rises and the PWM latch reset signal is removed allowing the main MOSFET Q1 to turn on at the beginning of the next clock set pulse. In boost and buck-boost topologies, the DDRV pin is used to control a N-channel MOSFET placed in series with the LED load, while it would control a P-channel MOSFET in parallel with the load for a buck topology. The series dimFET will open the LED load, when nDIM is low, effectively speeding up the rise and fall times of the LED current. Without any dimFET, the rise and fall times are limited by the inductor slew rate and dimming frequencies above 1 kHz are impractical. Using the series dimFET, dimming frequencies up to 30 kHz are achievable. With a parallel dimFET (buck topology), even higher dimming frequencies are achievable. When using the PWM functionality in a boost regulator, the PWM signal drives a ground referenced FET. However, with buck-boost and buck topologies, level shifting circuitry is necessary to translate the PWM dim signal to the floating dimFET as shown in Figure 32 and Figure 33. Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 23 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com Feature Description (continued) When using a series dimFET to PWM dim the LED current, more output capacitance is always better. A general rule of thumb is to use a minimum of 40 F when PWM dimming. For most applications, this will provide adequate energy storage at the output when the dimFET turns off and opens the LED load. Then when the dimFET is turned back on, the capacitance helps source current into the load, improving the LED current rise time. A minimum on-time must be maintained in order for PWM dimming to operate in the linear region of its transfer function. Because the controller is disabled during dimming, the PWM pulse must be long enough such that the energy intercepted from the input is greater than or equal to the energy being put into the LEDs. For boost and buck-boost regulators, the minimum dimming pulse length in seconds (tPULSE) is: 2 x ILED x VO X L1 tPULSE = VIN2 (34) Even maintaining a dimming pulse greater than tPULSE, preserving linearity at low dimming duty cycles is difficult. Several modifications are suggested for applications requiring low dimming duty cycles. Since nDIM rising releases the latch but does not trigger the on-time specifically, there will be an effective jitter on the rising edge of the LED current. This jitter can be easily removed by tying the PWM input signal through the synchronization network at the RT pin (shown in Figure 35), forcing the on-time to synchronize with the nDIM pulse. The second helpful modification is to remove the CFS capacitor and RFS resistor, eliminating the high frequency compensation pole. This should not affect stability, but it will speed up the response of the CSH pin, specifically at the rising edge of the LED current when PWM dimming, thus improving the achievable linearity at low dimming duty cycles. LED+ LM3424 10: 5 k: Q7 100 nF Q2 VCC Q6 Q4 RSNS 100 pF 10V VIN 500: DDRV Figure 32. Buck-boost Level-Shifted PWM Circuit LM3424 RSNS 100 k: 10V Q2 100 nF DDRV Figure 33. Buck Level-Shifted PWM Circuit 24 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 Feature Description (continued) 7.3.12 Thermal Shutdown The LM3424 includes thermal shutdown. If the die temperature reaches approximately 165C the device will shut down (GATE pin low), until it reaches approximately 140C where it turns on again. 7.4 Device Functional Modes There are no additional device functional modes for this part. Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 25 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com 8 Application and Implementation NOTE Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI's customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality. 8.1 Application Information 8.1.1 Inductor The inductor (L1) is the main energy storage device in a switching regulator. Depending on the topology, energy is stored in the inductor and transfered to the load in different ways (as an example, buck-boost operation is detailed in the Current Regulators section). The size of the inductor, the voltage across it, and the length of the switching subinterval (tON or tOFF) determines the inductor current ripple (iL-PP). In the design process, L1 is chosen to provide a desired iL-PP. For a buck regulator the inductor has a direct connection to the load, which is good for a current regulator. This requires little to no output capacitance therefore iL-PP is basically equal to the LED ripple current iLED-PP. However, for boost and buck-boost regulators, there is always an output capacitor which reduces iLED-PP, therefore the inductor ripple can be larger than in the buck regulator case where output capacitance is minimal or completely absent. In general, iLED-PP is recommended by manufacturers to be less than 40% of the average LED current (ILED). Therefore, for the buck regulator with no output capacitance, iL-PP should also be less than 40% of ILED. For the boost and buck-boost topologies, iL-PP can be much higher depending on the output capacitance value. However, iL-PP is suggested to be less than 100% of the average inductor current (IL) to limit the RMS inductor current. L1 is also suggested to have an RMS current rating at least 25% higher than the calculated minimum allowable RMS inductor current (IL-RMS). 8.1.2 LED Dynamic Resistance When the load is a string of LEDs, the output load resistance is the LED string dynamic resistance plus RSNS. LEDs are PN junction diodes, and their dynamic resistance shifts as their forward current changes. Dividing the forward voltage of a single LED (VLED) by the forward current (ILED) leads to an incorrect calculation of the dynamic resistance of a single LED (rLED). The result can be 5 to 10 times higher than the true rLED value. Figure 34. Dynamic Resistance Obtaining rLED is accomplished by referring to the manufacturer's LED I-V characteristic. It can be calculated as the slope at the nominal operating point as shown in Figure 34. For any application with more than 2 series LEDs, RSNS can be neglected allowing rD to be approximated as the number of LEDs multiplied by rLED. 26 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 Application Information (continued) 8.1.3 Output Capacitor For boost and buck-boost regulators, the output capacitor (CO) provides energy to the load when the recirculating diode (D1) is reverse biased during the first switching subinterval. An output capacitor in a buck topology will simply reduce the LED current ripple (iLED-PP) below the inductor current ripple (iL-PP). In all cases, CO is sized to provide a desired iLED-PP. As mentioned in the Inductor section, iLED-PP is recommended by manufacturers to be less than 40% of the average LED current (ILED). CO should be carefully chosen to account for derating due to temperature and operating voltage. It must also have the necessary RMS current rating. Ceramic capacitors are the best choice due to their high ripple current rating, long lifetime, and good temperature performance. An X7R dieletric rating is suggested. 8.1.4 Input Capacitors The input capacitance (CIN) provides energy during the discontinuous portions of the switching period. For buck and buck-boost regulators, CIN provides energy during tON and during tOFF, the input voltage source charges up CIN with the average input current (IIN). For boost regulators, CIN only needs to provide the ripple current due to the direct connection to the inductor. CIN is selected given the maximum input voltage ripple (vIN-PP) which can be tolerated. vIN-PP is suggested to be less than 10% of the input voltage (VIN). An input capacitance at least 100% greater than the calculated CIN value is recommended to account for derating due to temperature and operating voltage. When PWM dimming, even more capacitance can be helpful to minimize the large current draw from the input voltage source during the rising transistion of the LED current waveform. The chosen input capacitors must also have the necessary RMS current rating. Ceramic capacitors are again the best choice due to their high ripple current rating, long lifetime, and good temperature performance. An X7R dieletric rating is suggested. For most applications, it is recommended to bypass the VIN pin with an 0.1 F ceramic capacitor placed as close as possible to the pin. In situations where the bulk input capacitance may be far from the LM3424 device, a 10 series resistor can be placed between the bulk input capacitance and the bypass capacitor, creating a 150 kHz filter to eliminate undesired high frequency noise. 8.1.5 Main MOSFET and Dimming MOSFET The LM3424 requires an external NFET (Q1) as the main power MOSFET for the switching regulator. Q1 is recommended to have a voltage rating at least 15% higher than the maximum transistor voltage to ensure safe operation during the ringing of the switch node. In practice, all switching regulators have some ringing at the switch node due to the diode parasitic capacitance and the lead inductance. The current rating is recommended to be at least 10% higher than the average transistor current. The power rating is then verified by calculating the power loss given the RMS transistor current and the NFET on-resistance (RDS-ON). When PWM dimming, the LM3424 requires another MOSFET (Q2) placed in series (or parallel for a buck regulator) with the LED load. This MOSFET should have a voltage rating greater than the output voltage (VO) and a current rating at least 10% higher than the nominal LED current (ILED) . The power rating is simply VO multiplied by RDS-ON, assuming 100% dimming duty cycle (continuous operation) will occur. In general, the NFETs should be chosen to minimize total gate charge (Qg) when fSW is high and minimize RDS-ON otherwise. This will minimize the dominant power losses in the system. Frequently, higher current NFETs in larger packages are chosen for better thermal performance. 8.1.6 Re-Circulating Diode A re-circulating diode (D1) is required to carry the inductor current during tOFF. The most efficient choice for D1 is a Schottky diode due to low forward voltage drop and near-zero reverse recovery time. Similar to Q1, D1 is recommended to have a voltage rating at least 15% higher than the maximum transistor voltage to ensure safe operation during the ringing of the switch node and a current rating at least 10% higher than the average diode current. The power rating is verified by calculating the power loss through the diode. This is accomplished by checking the typical diode forward voltage from the I-V curve on the product datasheet and multiplying by the average diode current. In general, higher current diodes have a lower forward voltage and come in better performing packages minimizing both power losses and temperature rise. Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 27 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com Application Information (continued) 8.1.7 Switching Frequency The switching frequency of the LM3424 is programmed using an external resistor (RT) connected from the RT pin to GND as shown in Figure 35. Alternatively, an external PWM signal can be applied to the RT pin through a filter (RFLT and CFLT) and an AC coupling capacitor (CAC) to synchronize the part to an external clock as shown in Figure 35. If the external PWM signal is applied at a frequency higher than the base frequency set by the RT resistor, the internal oscillator is bypassed and the switching frequency becomes the synchronized frequency. The external synchronization signal should have a pulse width of 100ns, an amplitude between 3V and 6V, and be AC coupled to the RT pin with a ceramic capacitor (CAC = 100pF). A 10MHz RC filter (RFLT = 150 and CFLT = 100 pF) should be placed between the PWM signal and CAC to eliminate unwanted high frequency noise from coupling into the RT pin. The switching frequency is defined: 1 fSW = 1.4 x 10-10 x R T - 1.95 x 10 - 8 (35) See the Typical Characteristics section for a plot of RT vs. fSW. LM3424 External Synchronization RFLT Start tON CAC RT PWM CFLT Oscillator RT Figure 35. Timing Circuitry 28 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 8.2 Typical Applications 8.2.1 Basic Topology Schematics L1 D1 VIN CIN 1 RUV2 2 VIN LM3424 HSP HSN EN 20 RHSP 19 RHSN 18 RSLP CFS RSNS RFS CCMP RCSH RT 3 4 5 COMP SLOPE CSH IS RT/SYNC VCC 17 COUT ROV2 COV ROV1 ILED 16 CBYP RUVH 6 RUV1 CSS RGAIN 7 8 9 GATE nDIM GND SS DDRV TGAIN TSENSE OVP 15 Q1 14 RLIM 13 Q2 12 DAP RREF1 10 TREF VS 11 RREF2 RBIAS CREF Q3 CNTC PWM NTC Figure 36. Boost Regulator (VIN < VO) Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 29 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com Typical Applications (continued) VIN CIN 1 RUV2 2 LM3424 VIN HSP HSN EN 20 19 RHSP CFS RHSN RSNS RFS CCMP 3 COMP SLOPE 18 COUT RSLP RPU D2 RCSH 4 CSH IS 17 Q2 DIM RT 5 RT/SYNC VCC D1 16 L1 CBYP RUVH 6 GATE nDIM ROV2 ILED Q5 15 Q1 CSS RUV1 7 GND SS 14 RLIM RGAIN 8 TGAIN DDRV 13 DIM CDIM 9 OVP TSENSE 12 DAP RREF1 10 TREF VS COV 11 RREF2 CREF Q3 PWM ROV1 RBIAS NTC CNTC Figure 37. Buck Regulator (VIN > VO) 30 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 Typical Applications (continued) D1 VIN LED+ L1 CIN 1 RUV2 2 LM3424 VIN ILED HSP HSN EN RHSP DIM RHSN CFS 20 19 COUT Q2 RSNS VIN RFS CCMP 3 SLOPE COMP 18 RSLP LED+ RCSH RT 4 IS CSH RPU 17 Q7 DIM 5 VCC RT/SYNC 16 Q6 Q4 CBYP RUVH 6 RUV1 CSS RGAIN GATE nDIM ROV2 D2 15 Q5 Q1 VIN 7 8 9 GND SS TGAIN DDRV OVP TSENSE 14 RLIM RSER 13 12 DAP RREF1 10 TREF VS COV 11 RREF2 CREF Q3 PWM CNTC ROV1 RBIAS NTC Figure 38. Buck-Boost Regulator 8.2.1.1 Design Requirements Number of series LEDs: N Single LED forward voltage: VLED Single LED dynamic resistance: rLED Nominal input voltage: VIN Input voltage range: VIN-MAX, VIN-MIN Switching frequency: fSW Current sense voltage: VSNS Average LED current: ILED Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 31 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com Typical Applications (continued) Inductor current ripple: iL-PP LED current ripple: iLED-PP Peak current limit: ILIM Input voltage ripple: vIN-PP Output OVLO characteristics: VTURN-OFF, VHYSO Input UVLO characteristics: VTURN-ON, VHYS Thermal foldback characteristics: TBK, TEND Total start-up time: tTSU 8.2.1.2 Detailed Design Procedure 8.2.1.2.1 Operating Point Given the number of series LEDs (N), the forward voltage (VLED) and dynamic resistance (rLED) for a single LED, solve for the nominal output voltage (VO) and the nominal LED string dynamic resistance (rD): VO = N x VLED (36) rD = N x rLED (37) Solve for the ideal nominal duty cycle (D): Buck D= VO VIN (38) VO - VIN VO (39) Boost D= Buck-Boost D= VO VO + VIN (40) Using the same equations, find the minimum duty cycle (DMIN) using maximum input voltage (VIN-MAX) and the maximum duty cycle (DMAX) using the minimum input voltage (VIN-MIN). Also, remember that D' = 1 - D. 8.2.1.2.2 Switching Frequency Set the switching frequency (fSW) by solving for RT: RT 1 1.95x108 x fSW 1.40x1010 x fSW (41) 8.2.1.2.3 Average LED Current For all topologies, set the average LED current (ILED) knowing the desired current sense voltage (VSNS) and solving for RSNS: VSNS RSNS = ILED (42) If the calculated RSNS is too far from a desired standard value, then VSNS will have to be adjusted to obtain a standard value. Setup the suggested signal current of 100 A by assuming RCSH = 12.4 k and solving for RHSP: ILED x RCSH x RSNS RHSP = 1.24V 32 Submit Documentation Feedback (43) Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 Typical Applications (continued) If the calculated RHSP is too far from a desired standard value, then RCSH can be adjusted to obtain a standard value. 8.2.1.2.4 Thermal Foldback For all topologies, set the thermal foldback breakpoint (TBK) by finding corresponding RNTC-BK from manufacturer's datasheet and solving for RBIAS: RREF2 RBIAS = RNTC-BK x RREF1 (44) The easiest approach is to set RREF1 = RREF2, therefore setting RBIAS = RNTC-BK will properly set TBK. Remember, capacitance is recommended at the TSENSE and TREF pins, so ensure CREF > CNTC to prevent start-up in foldback. Then set the thermal foldback endpoint (TEND) by finding the corresponding RNTC-END from manufacturer's datasheet and solving for RGAIN: * R NTC - END R REF1 RREF1 + RREF2 - RNTC - END + RBIAS x 2.45V (c) R GAIN = ICSH (45) 8.2.1.2.5 Inductor Ripple Current Set the nominal inductor ripple current (iL-PP) by solving for the appropriate inductor (L1): Buck L1 = (VIN - VO) x D uiL - PP x fSW (46) Boost and Buck-boost VIN x D L1= uiL- PP x fSW (47) To set the worst case inductor ripple current, use VIN-MAX and DMIN when solving for L1. The minimum allowable inductor RMS current rating (IL-RMS) can be calculated as: Buck IL-RMS = ILED x 1 'IL-PP* x 1+ 12 ILED (c) 2 (48) Boost and Buck-Boost 1 'IL-PP x D' * x x 1+ IL-RMS = 12 ILED D' ILED 2 (c) (49) 8.2.1.2.6 LED Ripple Current Set the nominal LED ripple current (iLED-PP), by solving for the output capacitance (CO): Buck CO = 'iL - PP 8 x fSW x rD x 'iLED - PP (50) Boost and Buck-Boost ILED x D CO = rD xuiLED- PP x fSW (51) Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 33 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com Typical Applications (continued) To set the worst case LED ripple current, use DMAX when solving for CO. Remember, when PWM dimming it is recommended to use a minimum of 40 F of output capacitance to improve performance. The minimum allowable RMS output capacitor current rating (ICO-RMS) can be approximated: Buck ICO - RMS = uiLED - PP 12 (52) Boost and Buck-Boost ICO-RMS = ILED x DMAX 1-DMAX (53) 8.2.1.2.7 Peak Current Limit Set the peak current limit (ILIM) by solving for the transistor path sense resistor (RLIM): 245 mV R LIM = ILIM (54) 8.2.1.2.8 Slope Compensation For all topologies, the preferred method to set slope compensation is to ensure any duty cycle is attainable for the nominal VO and chosen L by solving for RSLP: 1.5x1013 x L1 VO xRT xRLIM RSLP (55) 8.2.1.2.9 Loop Compensation Using a simple first order peak current mode control model, neglecting any output capacitor ESR dynamics, the necessary loop compensation can be determined. First, the uncompensated loop gain (TU) of the regulator can be approximated: Buck TU = TU0 x 1 s * 1+ ZP1 (c) (56) Boost and Buck-Boost s * 1 ZZ1 (c) TU = TU0 x s * 1+ ZP1 (c) (57) Where the pole (P1) is approximated: Buck 3 ZP1 = Boost 1 rD x CO (58) 3 ZP1 = 2 rD x CO (59) Buck-Boost 34 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 Typical Applications (continued) 3 ZP1 = 1+ D rD x CO (60) And the RHP zero (Z1) is approximated: Boost rD x Dc2 L1 (61) Buck-Boost rD x Dc2 ZZ1 = D x L1 (62) ZZ1 = And the uncompensated DC loop gain (TU0) is approximated: Buck TU0 = 500V x RCSH x RSNS 620V = RHSP x R LIM ILED x RLIM (63) Dc x 500V x RCSH x RSNS Dc x 310V = 2 x RHSP x R LIM ILED x R LIM (64) Boost TU0 = Buck-Boost Dc x 500V x RCSH x RSNS Dc x 620V TU0 = = (1+ D) x RHSP x R LIM (1+ D) x ILED x R LIM (65) For all topologies, the primary method of compensation is to place a low frequency dominant pole (P2) which will ensure that there is ample phase margin at the crossover frequency. This is accomplished by placing a capacitor (CCMP) from the COMP pin to GND, which is calculated according to the lower value of the pole and the RHP zero of the system (shown as a minimizing function): min(Z P1, ZZ1) ZP2 = 5 x TU0 (66) CCMP 1 ZP2 x 5x106 (67) If analog dimming is used, CCMP should be approximately 4x larger to maintain stability as the LEDs are dimmed to zero. A high frequency compensation pole (P3) can be used to attenuate switching noise and provide better gain margin. Assuming RFS = 10, CFS is calculated according to the higher value of the pole and the RHP zero of the system (shown as a maximizing function): ZP3 = max (ZP1, ZZ1) x 10 1 CFS = 10 x ZP3 (68) (69) The total system loop gain (T) can then be written as: Buck T = TU0 x s * 1+ ZP1 x (c) 1 s * s * 1+ ZP2 x 1+ ZP3 (c) (c) (70) Boost and Buck-Boost Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 35 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com Typical Applications (continued) s * 1 ZZ1 (c) T = TU0 x s * s * s * 1+ ZP1 x 1+ ZP2 x 1+ ZP3 (c) (c) (c) (71) 8.2.1.2.10 Input Capacitance Set the nominal input voltage ripple (vIN-PP) by solving for the required capacitance (CIN): Buck CIN = ILED x (1 - D) x D 'VIN-PP x fSW (72) Boost CIN = 'iL-PP 8 x 'VIN-PP x fSW (73) Buck-Boost CIN = ILED x D 'VIN-PP x fSW (74) Use DMAX to set the worst case input voltage ripple, when solving for CIN in a buck-boost regulator and DMID = 0.5 when solving for CIN in a buck regulator. The minimum allowable RMS input current rating (ICIN-RMS) can be approximated: Buck ICIN - RMS = ILED x DMID x (1-DMID) (75) Boost ICIN-RMS = 'iL-PP 12 (76) Buck-Boost ICIN-RMS = ILED x DMAX 1-DMAX (77) 8.2.1.2.11 NFET The NFET voltage rating should be at least 15% higher than the maximum NFET drain-to-source voltage (VTMAX): Buck VT - MAX = VIN - MAX (78) Boost VT - MAX = VO (79) Buck-Boost VT - MAX = VIN - MAX + VO (80) The current rating should be at least 10% higher than the maximum average NFET current (IT-MAX): Buck IT-MAX = DMAX x ILED (81) Boost and Buck-Boost 36 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 Typical Applications (continued) IT-MAX = DMAX 1 - DMAX x ILED (82) Approximate the nominal RMS transistor current (IT-RMS) : Buck IT- RMS = ILED x D (83) Boost and Buck-Boost ILED x D IT - RMS = Dc (84) Given an NFET with on-resistance (RDS-ON), solve for the nominal power dissipation (PT): 2 PT = IT - RMS x R DSON (85) 8.2.1.2.12 Diode The Schottky diode voltage rating should be at least 15% higher than the maximum blocking voltage (VRD-MAX): Buck VRD-MAX = VIN-MAX (86) Boost VRD-MAX = VO (87) Buck-Boost VRD-MAX = VIN-MAX + VO (88) The current rating should be at least 10% higher than the maximum average diode current (ID-MAX): Buck ID-MAX = (1 - DMIN) x ILED (89) Boost and Buck-Boost ID-MAX = ILED (90) Replace DMAX with D in the ID-MAX equation to solve for the average diode current (ID). Given a diode with forward voltage (VFD), solve for the nominal power dissipation (PD): PD = ID x VFD (91) 8.2.1.2.13 Output OVLO For boost and buck-boost regulators, output OVLO is programmed with the turn-off threshold voltage (VTURN-OFF) and the desired hysteresis (VHYSO). To set VHYSO, solve for ROV2: VHYSO ROV2 = 20 PA (92) To set VTURN-OFF, solve for ROV1: Boost ROV1 = 1.24V x ROV2 VTURN - OFF - 1.24V (93) Buck-Boost R OV1 = 1.24V x R OV2 VTURN - OFF - 620 mV (94) Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 37 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com Typical Applications (continued) A small filter capacitor (COVP = 47 pF) should be added from the OVP pin to ground to reduce coupled switching noise. 8.2.1.2.14 Input UVLO For all topologies, input UVLO is programmed with the turn-on threshold voltage (VTURN-ON) and the desired hysteresis (VHYS). Method 1: If no PWM dimming is required, a two resistor network can be used. To set VHYS, solve for RUV2: VHYS RUV2 = 20 PA (95) To set VTURN-ON, solve for RUV1: 1.24V x RUV2 RUV1 = VTURN - ON - 1.24V (96) Method 2: If PWM dimming is required, a three resistor network is suggested. To set VTURN-ON, assume RUV2 = 10 k and solve for RUV1 as in Method 1. To set VHYS, solve for RUVH: RUVH = R UV1 x (VHYS - 20 PA x RUV2) 20 PA x (RUV1 + R UV2) (97) 8.2.1.2.15 Soft-Start For all topologies, if soft-start is desired, find the start-up time without CSS (tSU): t SU = t VCC + t CMP + t CO (98) Then, if the desired total start-up time (tTSU) is larger than tSU, solve for the base start-up time (tSU-SS-BASE), assuming that a CSS greater than 40% of CCMP will be used: V t SU - SS - BASE = 168: x CBYP + 28 k: x CCMP + O x CO ILED (99) Then solve for CSS: CSS = 10 PA x (t TSU - t SU - SS - BASE) 0.2V (100) 8.2.1.2.16 PWM Dimming Method PWM dimming can be performed several ways: Method 1: Connect the dimming MOSFET (Q3) with the drain to the nDIM pin and the source to GND. Apply an external PWM signal to the gate of QDIM. A pull down resistor may be necessary to properly turn off Q3. Method 2: Connect the anode of a Schottky diode to the nDIM pin. Apply an external inverted PWM signal to the cathode of the same diode. The DDRV pin should be connected to the gate of the dimFET with or without level-shifting circuitry as described in the PWM Dimming section. The dimFET should be rated to handle the average LED current and the nominal output voltage. 8.2.1.2.17 Analog Dimming Method Analog dimming can be performed several ways: Method 1: Place a potentiometer in place of the thermistor in the thermal foldback circuit shown in the Thermal Foldback and Analog Dimming section. Method 2: Place a potentiometer in series with the RCSH resistor to dim the LED current from the nominal ILED to near zero. Method 3: Connect a controlled current source as detailed in the Thermal Foldback and Analog Dimming section to the CSH pin. Increasing the current sourced into the CSH node will decrease the LEDs from the nominal ILED to zero current in the same manner as the thermal foldback circuit. 38 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 Typical Applications (continued) 8.2.2 Buck-Boost Application 10V 70V VIN D1 L1 CIN RHSP 1 RUV2 2 CCMP RCSH RT 3 4 5 LM3424 VIN HSP HSN EN COMP SLOPE CSH IS RT/SYNC VCC 20 19 1A ILED RHSN COUT 18 RSLP 17 CFS RSNS VIN 16 RFS CBYP 6 RUV1 CSS RGAIN 7 8 9 GATE nDIM GND SS DDRV TGAIN TSENSE OVP 15 Q1 14 ROV2 RLIM 13 VIN Q2 12 DAP RREF1 10 TREF VS COV 11 RREF2 CREF CNTC ROV1 RBIAS NTC Figure 39. Buck-Boost Application 8.2.2.1 Design Requirements N=6 VLED = 3.5V rLED = 325 m VIN = 24V VIN-MIN = 10V VIN-MAX = 70V fSW = 500 kHz VSNS = 100 mV Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 39 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com Typical Applications (continued) ILED = 1A iL-PP = 700 mA iLED-PP = 12 mA vIN-PP = 100 mV ILIM = 6A VTURN-ON = 10V VHYS = 3V VTURN-OFF = 40V VHYSO = 10V TBK = 70C TEND= 120C tTSU = 30 ms 8.2.2.2 Detailed Design Procedure 8.2.2.2.1 Operating Point Solve for VO and rD: VO = N x VLED = 6 x 3.5V = 21V (101) rD = N x rLED = 6 x 325 m: = 1. 95: (102) Solve for D, D', DMAX, and DMIN: VO 21V D= = = 0.467 VO + VIN 21V + 24V (103) (104) D' = 1 - D = 1 - 0. 467 = 0. 533 VO 21V = = 0.231 DMIN = VO + VIN-MAX 21V + 70V DMAX = (105) VO 21V = = 0.677 VO + VIN-MIN 21V + 10V (106) 8.2.2.2.2 Switching Frequency Solve for RT: -8 RT = 1+1.95 x 10 x fSW 1.4 x 10 - 10 x fSW -8 = 1+1.95 x 10 x 500 kHz = 14.4 k 1.4 x 10-10 x 500 kHz (107) The closest standard resistor is 14.3 k therefore fSW is: 1 fSW = - 10 1.4 x 10 x R T - 1.95 x 10 - 8 1 fSW = - 8 = 504 kHz - 10 1.4 x 10 x14.3 k - 1.95 x 10 (108) The chosen component from step 2 is: RT = 14.3 k: (109) 8.2.2.2.3 Average LED Current Solve for RSNS: 40 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 Typical Applications (continued) RSNS = VSNS 100 mV = = 0.1: ILED 1A (110) Assume RCSH = 12.4 k and solve for RHSP: ILED x RCSH x RSNS 1A x 12.4 k : x 0.1: RHSP = = = 1.0 k: 1.24V 1.24V (111) The closest standard resistor for RSNS is actually 0.1 and for RHSP is actually 1 k therefore ILED is: 1.24V x RHSP 1.24V x 1.0 k: ILED = = = 1.0A R SNS x R CSH 0.1: x 12.4 k: (112) The chosen components from step 3 are: RS NS = 0.1: R CSH = 12.4 k : RHSP = RHSN = 1 k: (113) 8.2.2.2.4 Thermal Foldback Find the resistances corresponding to TBK and TEND (RNTC-BK = 24.3 k and RNTC-END = 7.15 k) from the manufacturer's datasheet. Assuming RREF1 = RREF2 = 49.9 k, then RBIAS = RNTC-BK= 24.3 k. Solve for RGAIN: R GAIN = * R NTC - END RREF1 RREF1 + R REF2 - R NTC - END + RBIAS x 2.45V (c) ICSH 1 * 7.15 k: x 2.45V (c) 2 7.15 k: + 24.3 k: R GAIN = = 6.68 k: 100 PA (114) The chosen components from step 4 are: R GAIN = 6.81 k R BIAS = 24.3 k R REF1 = R REF2 = 49.9 k (115) 8.2.2.2.5 Inductor Ripple Current Solve for L1: VIN x D 24V x 0. 467 L1 = = = 32 PH 'iL- PP x fSW 700 mA x 504 kHz (116) The closest standard inductor is 33 H therefore iL-PP is: V xD 24V x 0. 467 'iL- PP = IN = 674 mA = L1 x fSW 33 PH x 504 kHz (117) Determine minimum allowable RMS current rating: 2 I 1 'iL - PP x Dc* x IL - RMS = LED x 1+ 12 (c) ILED Dc 2 IL - RMS = 1 674 mA x 0.533* 1.89A 1A x = x 1+ 1A 12 (c) 0. 533 (118) The chosen component from step 5 is: Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 41 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com Typical Applications (continued) L1 = 33 PH (119) 8.2.2.2.6 Output Capacitance Solve for CO: CO = CO = ILED x D rD x 'iLED- PP x fSW 1A x 0. 467 = 39.6 PF 1.95: x 12 mA x 5 04 kHz (120) The closest capacitance totals 40 F therefore iLED-PP is: I xD 'iLED- PP = LED rD x CO x fSW 'iLED- PP = 1A x 0. 467 = 12 mA 1.95 : x 40 PF x 5 04 kHz (121) Determine minimum allowable RMS current rating: ICO- RMS = ILED x DMAX 0.677 = 1.45A = 1A x 1- DMAX 1- 0.677 (122) The chosen components from step 6 are: CO = 4 x 10 PF (123) 8.2.2.2.7 Peak Current Limit Solve for RLIM: 245 mV 245 mV RLIM = = = 0.041: ILIM 6A (124) The closest standard resistor is 0.04 therefore ILIM is: 245 mV 245 mV ILIM = = = 6.13A RLIM 0.04 : (125) The chosen component from step 7 is: RLIM = 0.04: (126) 8.2.2.2.8 Slope Compensation Solve for RSLP: R SLP = R SLP = 1.5 x 1013 x L1 VO x R T x RLIM 1. 5 e13 x 33 H = 41.2 k 21 V x 14.3 k x 0.04 (127) The chosen component from step 8 is: R SLP = 41.2 k (128) 8.2.2.2.9 Loop Compensation P1 is approximated: rad 1.467 1+ D ZP1 = = = 19 k sec rD x CO 1.95: x 40 PF 42 Submit Documentation Feedback (129) Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 Typical Applications (continued) Z1 is approximated: rD x Dc2 1.95: x 0.5332 rad ZZ1 = = = 36k D x L1 0.467 x 33 PH sec (130) TU0 is approximated: 0.533 x 620V Dc x 620V TU0 = = = 5630 1 . 467 x 1A x 0.04: (1+ D) x ILED x R LIM (131) To ensure stability, calculate P2: rad 19k min(ZP1, ZZ1) ZP1 sec rad ZP2 = = = = 0. 675 5 x 5630 5 x 5630 5 x TU0 sec (132) Solve for CCMP: CCMP = 1 1 = = 0.30 F P2 x 5 x 106 0.675 rad x 5 x 10 6 sec (133) To attenuate switching noise, calculate P3: ZP3 = (max ZP1, ZZ1) x 10 = ZZ1 x 10 ZP3 = 36 k rad rad x 10 = 360k sec sec (134) Assume RFS = 10 and solve for CFS: 1 1 CFS = = = 0.28 PF rad 10: x ZP3 10: x 360k sec (135) The chosen components from step 9 are: CCMP = 0.33 PF RFS = 10: CFS = 0.27PF (136) 8.2.2.2.10 Input Capacitance Solve for the minimum CIN: ILED x D 1A x 0. 467 = 9.27 PF CIN = = 'vIN- PP x fSW 100 mV x 504 kHz (137) To minimize power supply interaction a 200% larger capacitance of approximately 20 F is used, therefore the actual vIN-PP is much lower. Since high voltage ceramic capacitor selection is limited, four 4.7 F X7R capacitors are chosen. Determine minimum allowable RMS current rating: IIN- RMS = ILED x DMAX 0.677 = 1.45A = 1A x 1- DMAX 1- 0.677 (138) The chosen components from step 10 are: CIN = 4 x 4.7 PF (139) 8.2.2.2.11 NFET Determine minimum Q1 voltage rating and current rating: VT - MAX = VIN - MAX + VO = 70V + 21V = 91V Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 (140) Submit Documentation Feedback 43 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com Typical Applications (continued) IT- MAX = 0. 677 x 1A = 2.1A 1- 0.677 (141) A 100V NFET is chosen with a current rating of 32A due to the low RDS-ON = 50 m. Determine IT-RMS and PT: ILED 1A IT - RMS = x 0.467 = 1. 28A x D= 0. 533 (142) Dc 2 PT = IT- RMS x RDSON = 1. 28A2 x 50 m: = 82 mW (143) The chosen component from step 11 is: Q1 o 32A, 100V, DPAK (144) 8.2.2.2.12 Diode Determine minimum D1 voltage rating and current rating: VRD - MAX = VIN - MAX + VO = 70V + 21V = 91V (145) ID - MAX = ILED = 1A (146) A 100V diode is chosen with a current rating of 12A and VDF = 600 mV. Determine PD: PD = ID x VFD = 1A x 600 mV = 600 mW (147) The chosen component from step 12 is: D1 o 12A, 100V, DPAK (148) 8.2.2.2.13 Input UVLO Solve for RUV2: VHYS 3V R UV2 = = = 150 k: 20 P A 20 PA (149) The closest standard resistor is 150 k therefore VHYS is: VHYS = RUV2 x 20 P A = 150 k: x 20 P A = 3V (150) Solve for RUV1: 1.24V x R UV2 1.24V x 150 k: R UV1 = = = 21.2 k: VTURN - ON - 1.24V 10V -1.24V (151) The closest standard resistor is 21 k making VTURN-ON: VTURN - ON = 1.24V x (R UV1 + R UV2) R UV1 VTURN- ON = 1.24V x (21 k: + 150 k:) = 10.1V 21 k: (152) The chosen components from step 13 are: RUV1 = 21 k: RUV2 = 150 k: (153) 8.2.2.2.14 Output OVLO Solve for ROV2: VHYSO 10V ROV2 = = = 500 k: 20 P A 20 P A (154) The closest standard resistor is 499 k therefore VHYSO is: 44 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 Typical Applications (continued) VHYSO = ROV2 x 20 PA = 499 k: x 20 PA = 9.98V (155) Solve for ROV1: 1.24V x ROV2 1.24V x 499 k: R OV1 = = = 15.7 k: VTURN - OFF - 0.62V 40V - 0.62V (156) The closest standard resistor is 15.8 k making VTURN-OFF: VTURN - OFF = 1.24V x (0.5 x R OV1 + R OV2) R OV1 VTURN- OFF = 1.24V x (0.5 x15.8 k: + 499 k:) = 39.8V 15.8 k: (157) The chosen components from step 14 are: ROV1 = 15.8 k: ROV2 = 499 k: (158) 8.2.2.2.15 Soft-Start Solve for tSU: t SU = 168: x CBYP + 36 k: x CCMP + VO x CO ILED t SU = 168: x 2.2 PF + 36 k: x 0. 33 PF + 21V x 40 PF 1A t SU = 13.1 ms (159) If tSU is less than tTSU, solve for tSU-SS-BASE: t SU - SS - BASE = 168: x CBYP + 28 k: x CCMP + VO x CO ILED t SU SS BASE = 168: x 2.2 PF + 28 k: x 0. 33 PF + 21V x 40 PF 1A t SU SS BASE = 10.5 ms (160) Solve for CSS: (t TSU - t SU - SS - BASE) (30 ms - 10.5 ms) CSS = = 975 nF = 20 k : 20 k : (161) The chosen component from step 15 is: CSS = 1 PF (162) Table 1. Bill of Materials QTY PART ID PART VALUE MANUFACTURER PART NUMBER 1 LM3424 Boost controller TI LM3424MH 1 CBYP 2.2 F X7R 10% 16V MURATA GRM21BR71C225KA12L 2 CCMP, CNTC 0.33 F X7R 10% 25V MURATA GRM21BR71E334KA01L 1 CFS 0.27 F X7R 10% 25V MURATA GRM21BR71E274KA01L 4 CIN 4.7 F X7R 10% 100V TDK C5750X7R2A475K 4 CO 10 F X7R 10% 50V TDK C4532X7R1H106K 1 COV 47 pF COG/NPO 5% 50V AVX 08055A470JAT2A 1 CREF, CSS 1 F X7R 10% 25V MURATA GRM21BR71E105KA01L Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 45 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com Typical Applications (continued) Table 1. Bill of Materials (continued) QTY PART ID PART VALUE MANUFACTURER PART NUMBER 1 D1 Schottky 100V 12A VISHAY 12CWQ10FNPBF 1 L1 33 H 20% 6.3A COILCRAFT MSS1278-333MLB 1 Q1 NMOS 100V 32A FAIRCHILD FDD3682 1 Q2 PNP 150V 600 mA FAIRCHILD MMBT5401 1 RBIAS 24.3 k 1% VISHAY CRCW080524K3FKEA 1 RCSH 12.4 k 1% VISHAY CRCW080512K4FKEA 1 RFS 10 1% VISHAY CRCW080510R0FKEA 1 RGAIN 6.81 k 1% VISHAY CRCW08056K81FKEA 2 RHSP, RHSN 1.0 k 1% VISHAY CRCW08051K00FKEA 1 RLIM 0.04 1% 1W VISHAY WSL2512R0400FEA 1 ROV1 15.8 k 1% VISHAY CRCW080515K8FKEA 1 ROV2 499 k 1% VISHAY CRCW0805499KFKEA 2 RREF1, RREF2 49.9 k 1% VISHAY CRCW080549K9FKEA 1 RSLP 16.5 k 1% VISHAY CRCW080516K5FKEA 1 RSNS 0.1 1% 1W VISHAY WSL2512R1000FEA 1 RT 14.3 k 1% VISHAY CRCW080514K3FKEA 1 RUV1 21 k 1% VISHAY CRCW080521K0FKEA 1 RUV2 150 k 1% VISHAY CRCW0805150KFKEA 1 NTC Thermistor 100 k 5% TDK NTCG204H154J 8.2.2.3 Application Curve 100 EFFICIENCY (%) 95 90 85 80 75 70 0 16 32 48 64 80 VIN (V) Figure 40. Efficiency vs. Input Voltage 46 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 8.2.3 Boost Application 8V 28V VIN D1 L1 CIN RHSP 1 RUV2 2 LM3424 VIN HSP HSN EN 20 19 CFS RHSN RSNS RFS CCMP RCSH RT 3 4 5 COMP SLOPE CSH IS RT/SYNC VCC 18 RSLP 17 1A ILED 16 COUT CBYP RUVH RUV1 CSS RGAIN 6 7 8 9 GATE nDIM GND SS DDRV TGAIN TSENSE OVP 15 Q1 14 RLIM 13 Q2 ROV2 12 DAP RREF1 10 TREF VS COV 11 RREF2 CREF Q3 CNTC PWM ROV1 RBIAS NTC Figure 41. Boost Application 8.2.3.1 Design Requirements * Input: 8 V to 28 V * Output: 9 LEDs at 1A * 65C - 100C Thermal Foldback * PWM Dimming up to 30 kHz * 700 kHz Switching Frequency Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 47 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com 8.2.3.2 Detailed Design Procedure Table 2. Bill of Materials QTY PART ID PART VALUE MANUFACTURER PART NUMBER 1 LM3424 Boost controller TI LM3424MH 1 CBYP 2.2 F X7R 10% 16V MURATA GRM21BR71C225KA12L 1 CCMP 0.1 F X7R 10% 25V MURATA GRM21BR71E104KA01L 0 CFS DNP 4 CIN 4.7 F X7R 10% 100V TDK C5750X7R2A475K 4 COUT 10 F X7R 10% 50V TDK C4532X7R1H106K 1 COV 47 pF COG/NPO 5% 50V AVX 08055A470JAT2A 2 CNTC, CSS 0.27 F X7R 10% 25V MURATA GRM21BR71E274KA01L 1 CREF 1 F X7R 10% 25V MURATA GRM21BR71E105KA01L 1 D1 Schottky 60V 5A COMCHIP CDBC560-G 1 L1 33 H 20% 6.3A COILCRAFT MSS1278-333MLB 2 Q1, Q2 NMOS 60V 8A VISHAY SI4436DY 1 Q3 NMOS 60V 115mA ON-SEMI 2N7002ET1G 1 RBIAS 19.6 k 1% VISHAY CRCW080519K6FKEA 2 RCSH, ROV1 12.4 k 1% VISHAY CRCW080512K4FKEA 1 RFS 0 1% VISHAY CRCW08050000Z0EA 1 RGAIN 6.49 k 1% VISHAY CRCW08056K49FKEA 2 RHSP, RHSN 1.0 k 1% VISHAY CRCW08051K00FKEA 1 RLIM 0.06 1% 1W VISHAY WSL2512R0600FEA 1 ROV2 499 k 1% VISHAY CRCW0805499KFKEA 2 RREF1, RREF2 49.9 k 1% VISHAY CRCW080549K9FKEA 1 RSNS 0.1 1% 1W VISHAY WSL2512R1000FEA 2 RSLP, RUV2 10.0 k 1% VISHAY CRCW080510K0FKEA 1 RT 14.3 k 1% VISHAY CRCW080514K3FKEA 1 RUV1 1.82 k 1% VISHAY CRCW08051K82FKEA 1 RUVH 17.8 k 1% VISHAY CRCW080517K8FKEA 1 NTC Thermistor 100 k 5% TDK NTCG204H154J 48 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 8.2.4 Buck-Boost Application 10V 30V VIN D1 L1 CIN 2A ILED RHSP 1 RUV2 2 CCMP RCSH RT 3 LM3424 VIN HSP COUT HSN EN COMP 20 SLOPE 19 18 RHSN Q2 DIM RSLP CFS RSNS VIN 4 5 CSH IS RT/SYNC VCC RFS 17 RPU 16 Q7 RUV1 CSS 6 GATE nDIM 15 Q6 Q1 GND SS 14 RLIM ROV2 Q4 CB 7 CF DIM CBYP RUVH RF D2 Q5 RSER VIN RGAIN 8 9 DDRV TGAIN TSENSE OVP 13 12 DAP RREF1 10 TREF VS COV 11 RREF2 CREF Q3 CNTC PWM ROV1 RBIAS RPOT Figure 42. Buck-Boost Application 8.2.4.1 Design Requirements * Input: 10V to 30V * Output: 4 LEDs at 2A * PWM Dimming up to 10 kHz * Analog Dimming * 600-kHz Switching Frequency Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 49 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com 8.2.4.2 Detailed Design Procedures Table 3. Bill of Materials QTY PART ID PART VALUE MANUFACTURER PART NUMBER 1 LM3424 Boost controller TI LM3424MH 1 CB 100 pF COG/NPO 5% 50V MURATA GRM2165C1H101JA01D 1 CBYP 2.2 F X7R 10% 16V MURATA GRM21BR71C225KA12L 3 CCMP, CREF, CSS 1 F X7R 10% 25V MURATA GRM21BR71E105KA01L 1 CF 0.1 F X7R 10% 25V MURATA GRM21BR71E104KA01L 0 CFS DNP 4 CIN 6.8 F X7R 10% 50V TDK C5750X7R1H685K 1 CNTC 0.47 F X7R 10% 25V MURATA GRM21BR71E474KA01L 4 COUT 10 F X7R 10% 50V TDK C4532X7R1H106K 1 COV 47 pF COG/NPO 5% 50V AVX 08055A470JAT2A 1 D1 Schottky 100V 12A VISHAY 12CWQ10FNPBF 1 D2 Zener 10V 500mA ON-SEMI BZX84C10LT1G 1 L1 22 H 20% 7.2A COILCRAFT MSS1278-223MLB 2 Q1, Q2 NMOS 60V 8A VISHAY SI4436DY 1 Q3 NMOS 60V 260mA ON-SEMI 2N7002ET1G 1 Q4 PNP 40V 200 mA FAIRCHILD MMBT5087 1 Q5 PNP 150V 600 mA FAIRCHILD MMBT5401 1 Q6 NPN 300V 600 mA FAIRCHILD MMBTA42 1 Q7 NPN 40V 200 mA FAIRCHILD MMBT6428 3 RBIAS, RREF1, RREF2 49.9 k 1% VISHAY CRCW080549K9FKEA 2 RCSH, RT 12.4 k 1% VISHAY CRCW080512K4FKEA 1 RF 10 1% VISHAY CRCW080510R0FKEA 1 RFS 0 1% VISHAY CRCW08050000Z0EA 2 RGAIN, RUV2 10.0 k 1% VISHAY CRCW080510K0FKEA 2 RHSP, RHSN 1.0 k 1% VISHAY CRCW08051K00FKEA 1 RLIM 0.04 1% 1W VISHAY WSL2512R0400FEA 1 ROV1 18.2 k 1% VISHAY CRCW080518K2FKEA 1 ROV2 499 k 1% VISHAY CRCW0805499KFKEA 1 RPOT 50 k potentiometer BOURNS 3352P-1-503 1 RPU 4.99 k 1% VISHAY CRCW08054K99FKEA 1 RSER 499 1% VISHAY CRCW0805499RFKEA 1 RSLP 34.0 k 1% VISHAY CRCW080534K0FKEA 1 RSNS 0.05 1% 1W VISHAY WSL2512R0500FEA 1 RUV1 1.43 k 1% VISHAY CRCW08051K43FKEA 1 RUVH 17.4 k 1% VISHAY CRCW080517K4FKEA 50 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 8.2.5 Boost Application 18V 38V VIN D1 L1 CIN RHSP 1 VCC 2 VIN LM3424 HSP HSN EN 20 CFS RHSN 19 VS RSNS RFS Q4 Q3 CCMP 3 RMAX 4 Q2 RADJ RBIAS2 RCSH COMP SLOPE CSH IS 17 RT 5 RT/SYNC VCC COUT 700 mA ILED VCC RUV2 16 CBYP 6 RUV1 RSLP 18 CSS 7 RGAIN 8 9 GATE nDIM GND SS DDRV TGAIN TSENSE OVP 15 Q1 14 RLIM 13 ROV2 12 DAP RREF1 10 TREF VS VS COV 11 RREF2 CREF CNTC ROV1 RBIAS NTC Figure 43. Boost Application 8.2.5.1 Design Requirements * Input: 18V to 38V * Output: 12 LEDs at 700mA * 85C - 125C Thermal Foldback * Analog Dimming * 700 kHz Switching Frequency Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 51 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com 8.2.5.2 Detailed Design Procedure Table 4. Bill of Materials QTY PART ID PART VALUE MANUFACTURER PART NUMBER 1 LM3424 Boost controller TI LM3424MH 1 CBYP 2.2 F X7R 10% 16V MURATA GRM21BR71C225KA12L 3 CCMP, CREF, CSS 1 F X7R 10% 25V MURATA GRM21BR71E105KA01L 1 CNTC 0.33 F X7R 10% 25V MURATA GRM21BR71E334KA01L 1 CFS 0.1 F X7R 10% 25V MURATA GRM21BR71E104KA01L 4 CIN 4.7 F X7R 10% 100V TDK C5750X7R2A475K 4 COUT 10 F X7R 10% 50V TDK C4532X7R1H106K 1 COV 47 pF COG/NPO 5% 50V AVX 08055A470JAT2A 1 D1 Schottky 60V 5A COMCHIP CDBC560-G 1 L1 47 H 20% 5.3A COILCRAFT MSS1278-473MLB 1 Q1 NMOS 60V 8A VISHAY SI4436DY 1 Q2 NPN 40V 200 mA FAIRCHILD MMBT3904 1 Q3, Q4 (dual pack) Dual PNP 40V 200mA FAIRCHILD FFB3906 1 RADJ 100 k potentiometer BOURNS 3352P-1-104 1 RBIAS 9.76 k 1% VISHAY CRCW08059K76FKEA 1 RBIAS2 17.4 k 1% VISHAY CRCW080517K4FKEA 3 RCSH, ROV1, RUV1 12.4 k 1% VISHAY CRCW080512K4FKEA 1 RFS 10 1% VISHAY CRCW080510R0FKEA 1 RGAIN 6.55 k 1% VISHAY CRCW08056K55FKEA 3 RHSP, RHSN, RMAX 1.0 k 1% VISHAY CRCW08051K00FKEA 1 RLIM 0.06 1% 1W VISHAY WSL2512R0600FEA 1 ROV2 499 k 1% VISHAY CRCW0805499KFKEA 2 RREF1, RREF2 49.9 k 1% VISHAY CRCW080549K9FKEA 2 RSLP, RT 10.0 k 1% VISHAY CRCW080510K0FKEA 1 RSNS 0.15 1% 1W VISHAY WSL2512R1500FEA 1 RUV2 100 k 1% VISHAY CRCW0805100KFKEA 1 NTC Thermistor 100 k 5% TDK NTCG204H154J 52 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 8.2.6 Buck-Boost Application 10V 70V VIN D1 L1 CIN RHSP 1 RUV2 2 CCMP RCSH 3 4 LM3424 VIN HSP HSN EN COMP SLOPE CSH IS 20 19 18 500 mA ILED COUT RHSN RSLP DIM 17 Q2 CFS RSNS VIN RT 5 RT/SYNC VCC RFS 16 RF CBYP RUVH 6 GATE nDIM Q7 RPU 15 CF Q1 DIM CSS RUV1 RGAIN 7 GND SS Q6 14 8 9 DDRV TGAIN TSENSE OVP Q4 CB RSER ROV2 D2 Q5 13 VIN 12 DAP RREF1 10 TREF VS RREF2 CREF Q3 COV 11 ROV1 RBIAS CNTC PWM Figure 44. Buck-Boost Application 8.2.6.1 Design Requirements * Input: 10 V to 70 V * Output: 6 LEDs at 500 mA * PWM Dimming up to 10 kHz * 5-s Fade-up * MOSFET RDS-ON Sensing * 700-kHz Switching Frequency Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 53 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com 8.2.6.2 Detailed Design Procedure Table 5. Bill of Materials QTY PART ID PART VALUE MANUFACTURER PART NUMBER 1 LM3424 Boost controller TI LM3424MH 1 CB 100 pF COG/NPO 5% 50V MURATA GRM2165C1H101JA01D 1 CBYP 2.2 F X7R 10% 16V MURATA GRM21BR71C225KA12L 2 CCMP, CSS 1 F X7R 10% 25V MURATA GRM21BR71E105KA01L 1 CREF 0.01 F X7R 10% 25V MURATA GRM21BR71E103KA01L 1 CF 0.1 F X7R 10% 25V MURATA GRM21BR71E104KA01L 0 CFS DNP 4 CIN 4.7 F X7R 10% 100V TDK C5750X7R2A475K 1 CNTC 10 F X7R 10% 10V MURATA GRM21BR71A106KE51L 4 COUT 10 F X7R 10% 50V TDK C4532X7R1H106K 1 COV 47 pF COG/NPO 5% 50V AVX 08055A470JAT2A 1 D1 Schottky 100V 12A VISHAY 12CWQ10FNPBF 1 D2 Zener 10V 500mA ON-SEMI BZX84C10LT1G 1 L1 68 H 20% 4.3A COILCRAFT MSS1278-683MLB 2 Q1, Q2 NMOS 100V 32A FAIRCHILD FDD3682 1 Q3 NMOS 60V 260mA ON-SEMI 2N7002ET1G 1 Q4 PNP 40V 200mA FAIRCHILD MMBT5087 1 Q5 PNP 150V 600 mA FAIRCHILD MMBT5401 1 Q6 NPN 300V 600mA FAIRCHILD MMBTA42 1 Q7 NPN 40V 200mA FAIRCHILD MMBT6428 3 RBIAS, RREF1, RREF2 49.9 k 1% VISHAY CRCW080549K9FKEA 1 RCSH 12.4 k 1% VISHAY CRCW080512K4FKEA 1 RFS 0 1% VISHAY CRCW08050000Z0EA 3 RGAIN, RT, RUV2 10.0 k 1% VISHAY CRCW080510K0FKEA 2 RHSP, RHSN 1.0 k 1% VISHAY CRCW08051K00FKEA 1 ROV1 15.8 k 1% VISHAY CRCW080515K8FKEA 1 ROV2 499 k 1% VISHAY CRCW0805499KFKEA 1 RPU 4.99 k 1% VISHAY CRCW08054K99FKEA 1 RSER 499 1% VISHAY CRCW0805499RFKEA 1 RSNS 0.2 1% 1W VISHAY WSL2512R2000FEA 1 RSLP 24.3 k 1% VISHAY CRCW080524K3FKEA 1 RUV1 1.43 k 1% VISHAY CRCW08051K43FKEA 1 RUVH 17.4 k 1% VISHAY CRCW080517K4FKEA 54 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 8.2.7 Buck Application 15V 50V VIN L1 CIN RHSP 1 RUV2 2 VIN LM3424 HSP HSN EN 20 19 CFS RHSN RSNS RFS CCMP 3 COMP SLOPE 18 CO RSLP RPU RCSH RT 4 5 CSH IS RT/SYNC VCC D2 17 ROV2 Q2 1.25A ILED D1 16 L1 CBYP RUVH RUV1 CSS RGAIN 6 7 8 9 GATE nDIM GND SS DDRV TGAIN TSENSE OVP Q4 15 Q1 14 CDIM RLIM 13 12 DAP RREF1 10 TREF VS COV 11 RREF2 CREF Q3 CNTC PWM ROV1 RBIAS RPOT Figure 45. Buck Application 8.2.7.1 Design Requirements * Input: 15 V to 50 V * Output: 3 LEDS AT 1.25 A * PWM Dimming up to 50 kHz * Analog Dimming * 700-kHz Switching Frequency Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 55 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com 8.2.7.2 Detailed Design Procedure Table 6. Bill of Materials QTY PART ID PART VALUE MANUFACTURER PART NUMBER 1 LM3424 Boost controller TI LM3424MH 1 CBYP 2.2 F X7R 10% 16V MURATA GRM21BR71C225KA12L 2 CCMP, CDIM 0.1 F X7R 10% 25V MURATA GRM21BR71E104KA01L 0 CFS DNP 1 CNTC 0.33 F X7R 10% 25V MURATA GRM21BR71E334KA01L 4 CIN 4.7 F X7R 10% 100V TDK C5750X7R2A475K 0 COUT DNP 1 COV 47 pF COG/NPO 5% 50V AVX 08055A470JAT2A 1 CREF, CSS 1 F X7R 10% 25V MURATA GRM21BR71E105KA01L 1 D1 Schottky 100V 12A VISHAY 12CWQ10FNPBF 1 D2 Zener 10V 500mA ON-SEMI BZX84C10LT1G 1 L1 22 H 20% 7.3A COILCRAFT MSS1278-223MLB 1 Q1 NMOS 60V 8A VISHAY SI4436DY 1 Q2 PMOS 30V 6.2A VISHAY SI3483DV 1 Q3 NMOS 60V 115mA ON-SEMI 2N7002ET1G 1 Q4 PNP 150V 600 mA FAIRCHILD MMBT5401 3 RBIAS, RREF1, RREF2 49.9 k 1% VISHAY CRCW080549K9FKEA 1 RCSH 12.4 k 1% VISHAY CRCW080512K4FKEA 1 RFS 0 1% VISHAY CRCW08050000OZEA 1 RGAIN, RT 10.0 k 1% VISHAY CRCW080510K0FKEA 2 RHSP, RHSN 1.0 k 1% VISHAY CRCW08051K00FKEA 1 RLIM 0.04 1% 1W VISHAY WSL2512R0400FEA 1 ROV1 21.5 k 1% VISHAY CRCW080521K5FKEA 1 ROV2 499 k 1% VISHAY CRCW0805499KFKEA 1 RPOT 50 k potentiometer BOURNS 3352P-1-503 2 RPU, RUV2 100 k 1% VISHAY CRCW0805100KFKEA 1 RSLP 36.5 k 1% VISHAY CRCW080536K5FKEA 1 RSNS 0.08 1% 1W VISHAY WSL2512R0800FEA 1 RUV1 11.5 k 1% VISHAY CRCW080511K5FKEA 56 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 8.2.8 Buck-Boost Application 15V 60V VIN D1 L1 CIN RHSP 1 RUV2 2 CCMP RCSH 3 4 LM3424 VIN HSP COUT HSN EN SLOPE COMP CSH 20 IS 19 18 RHSN 2.5A ILED RSLP 17 RT CFLT CAC 5 RT/SYNC VCC SYNC 6 CSS RGAIN 7 8 9 GATE nDIM GND SS TGAIN DDRV OVP TSENSE RFS 15 14 RSNS VIN CBYP RFLT RUV1 CFS 16 Q1 ROV2 RLIM VIN 13 Q2 12 DAP RREF1 10 VS TREF COV 11 ROV1 RREF2 CREF RBIAS CNTC NTC Figure 46. Buck-Boost Application 8.2.8.1 Design Requirements * Input: 15 V to 60 V * Output: 8 LEDs at 2.5 A * 80C to 110C Thermal Foldback * 500-kHz Switching Frequency * External Synchronization > 500 kHz Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 57 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com 8.2.8.2 Detailed Design Procedure Table 7. Bill of Materials QTY PART ID PART VALUE MANUFACTURER PART NUMBER 1 LM3424 Boost controller TI LM3424MH 2 CAC, CFLT 100 pF COG/NPO 5% 50V MURATA GRM2165C1H101JA01D 1 CBYP 2.2 F X7R 10% 16V MURATA GRM21BR71C225KA12L 3 CCMP, CNTC, CSS 0.33 F X7R 10% 25V MURATA GRM21BR71E334KA01L 1 CFS 0.1 F X7R 10% 25V MURATA GRM21BR71E104KA01L 4 CIN 4.7 F X7R 10% 100V TDK C5750X7R2A475K 4 COUT 10 F X7R 10% 50V TDK C4532X7R1H106K 1 COV 47 pF COG/NPO 5% 50V AVX 08055A470JAT2A 1 CREF 1 F X7R 10% 25V MURATA GRM21BR71E105KA01L 1 D1 Schottky 100V 12A VISHAY 12CWQ10FNPBF 1 L1 22 H 20% 7.2A COILCRAFT MSS1278-223MLB 1 Q1 NMOS 100V 32A FAIRCHILD FDD3682 1 Q2 PNP 150V 600 mA FAIRCHILD MMBT5401 1 RBIAS 11.5 k 1% VISHAY CRCW080511K5FKEA 2 RCSH, ROV1 12.4 k 1% VISHAY CRCW080512K4FKEA 1 RFS 10 1% VISHAY CRCW080510R0FKEA 1 RFLT 150 1% VISHAY CRCW0805150RFKEA 1 RGAIN 5.49 k 1% VISHAY CRCW08055K49FKEA 2 RHSP, RHSN 1.0 k 1% VISHAY CRCW08051K00FKEA 2 RLIM, RSNS 0.04 1% 1W VISHAY WSL2512R0400FEA 1 ROV1 15.8 k 1% VISHAY CRCW080515K8FKEA 1 ROV2 499 k 1% VISHAY CRCW0805499KFKEA 2 RREF1, RREF2 49.9 k 1% VISHAY CRCW080549K9FKEA 1 RSLP 20.5 k 1% VISHAY CRCW080520K5FKEA 1 RT 14.3 k 1% VISHAY CRCW080514K3FKEA 1 RUV1 13.7 k 1% VISHAY CRCW080513K7FKEA 1 RUV2 150 k 1% VISHAY CRCW0805150KFKEA 1 NTC Thermistor 100 k 5% TDK NTCG204H154J 58 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 8.2.9 SEPIC Application 9V 36V VIN D1 L1 CIN CSEP L2 RHSP 1 RUV2 2 LM3424 VIN HSP HSN EN 20 19 CFS RHSN RSNS RFS CCMP RCSH RT 3 4 5 COMP SLOPE CSH IS RT/SYNC VCC 18 RSLP 17 750 mA ILED 16 COUT CBYP RUVH RUV1 CSS RGAIN 6 7 8 9 GATE nDIM GND SS DDRV TGAIN TSENSE OVP 15 Q1 14 RLIM 13 Q2 ROV2 12 DAP RREF1 10 TREF VS COV 11 RREF2 CREF Q3 CNTC PWM ROV1 RBIAS NTC Figure 47. SEPIC Application 8.2.9.1 Design Requirements * Input: 9 V to 36 V * Output: 5 LEDs at 750 mA * 60C to 120C Thermal Foldback * PWM Dimming up to 30 kHz * 500-kHz Switching Frequency Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 59 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com 8.2.9.2 Detailed Design Procedure Table 8. Bill of Materials QTY PART ID PART VALUE MANUFACTURER PART NUMBER 1 LM3424 Boost controller TI LM3424MH 1 CBYP 2.2 F X7R 10% 16V MURATA GRM21BR71C225KA12L 3 CCMP, CNTC, CSS 0.47 F X7R 10% 25V MURATA GRM21BR71E474KA01L 0 CFS DNP 4 CIN 4.7 F X7R 10% 100V TDK C5750X7R2A475K 4 COUT 10 F X7R 10% 50V TDK C4532X7R1H106K 1 CSEP 1.0 F X7R 10% 100V TDK C4532X7R2A105K 1 COV 47 pF COG/NPO 5% 50V AVX 08055A470JAT2A 1 CREF 1 F X7R 10% 25V MURATA GRM21BR71E105KA01L 1 D1 Schottky 60V 5A COMCHIP CDBC560-G 2 L1, L2 68 H 20% 4.3A COILCRAFT DO3340P-683 2 Q1, Q2 NMOS 60V 8A VISHAY SI4436DY 1 Q3 NMOS 60V 115 mA ON-SEMI 2N7002ET1G 1 RBIAS 23.7 k 1% VISHAY CRCW080523K7FKEA 1 RCSH 12.4 k 1% VISHAY CRCW080512K4FKEA 1 RFS 0 1% VISHAY CRCW08050000OZEA 1 RGAIN 9.31 k 1% VISHAY CRCW08059K31FKEA 2 RHSP, RHSN 750 1% VISHAY CRCW0805750RFKEA 1 RLIM 0.04 1% 1W VISHAY WSL2512R0400FEA 1 ROV1 15.8 k 1% VISHAY CRCW080515K8FKEA 1 ROV2 499 k 1% VISHAY CRCW0805499KFKEA 2 RREF1, RREF2 49.9 k 1% VISHAY CRCW080549K9FKEA 1 RSLP 20.0 k 1% VISHAY CRCW080520K0FKEA 1 RSNS 0.1 1% 1W VISHAY WSL2512R1000FEA 1 RT 14.3 k 1% VISHAY CRCW080514K3FKEA 1 RUV1 1.62 k 1% VISHAY CRCW08051K62FKEA 1 RUV2 10.0 k 1% VISHAY CRCW080510K0FKEA 1 RUVH 16.9 k 1% VISHAY CRCW080516K9FKEA 1 NTC Thermistor 100 k 5% TDK NTCG204H154J 60 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 9 Power Supply Recommendations 9.1 Input Supply Current Limit It is important to set the output current limit of your input supply to an appropriate value to avoid delays in your converter analysis and optimization. If not set high enough, current limit can be tripped during start up or when your converter output power is increased, causing a foldback or shut-down condition. It is a common oversight when powering up a converter for the first time. 10 Layout 10.1 Layout Guidelines The performance of any switching regulator depends as much upon the layout of the PCB as the component selection. Following a few simple guidelines will maximimize noise rejection and minimize the generation of EMI within the circuit. Discontinuous currents are the most likely to generate EMI, therefore care should be taken when routing these paths. The main path for discontinuous current in the LM3424 buck regulator contains the input capacitor (CIN), the recirculating diode (D1), the N-channel MOSFET (Q1), and the sense resistor (RLIM). In the LM3424 boost regulator, the discontinuous current flows through the output capacitor (CO), D1, Q1, and RLIM. In the buck-boost regulator both loops are discontinuous and should be carefully layed out. These loops should be kept as small as possible and the connections between all the components should be short and thick to minimize parasitic inductance. In particular, the switch node (where L1, D1, and Q1 connect) should be just large enough to connect the components. To minimize excessive heating, large copper pours can be placed adjacent to the short current path of the switch node. The RT, COMP, CSH, IS, TSENSE, TREF, HSP, and HSN pins are all high-impedance inputs which couple external noise easily, therefore the loops containing these nodes should be minimized whenever possible. In some applications the LED or LED array can be far away (several inches or more) from the LM3424, or on a separate PCB connected by a wiring harness. When an output capacitor is used and the LED array is large or separated from the rest of the regulator, the output capacitor should be placed close to the LEDs to reduce the effects of parasitic inductance on the AC impedance of the capacitor. Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 61 LM3424, LM3424-Q1 SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 www.ti.com 10.2 Layout Example Note critical paths and component placement: Minimize power loop containing discontinuous currents Minimize signal current loops (components close to IC) x Ground plane under IC for signal routing helps minimize noise coupling discontinuous switching frequency currents VIN 1 Input Power GND 2 3 4 5 6 PWM 7 8 9 TEMP VIN LM3424 EN HSP HSN COMP SLOPE CSH IS RT/SYNC VCC GATE nDIM GND SS DDRV TGAIN TSENSE OVP 20 19 18 17 16 15 14 13 12 DAP 10 TREF ILED STAR GROUND VS 11 Power Ground Figure 48. Layout Recommendation 62 Submit Documentation Feedback Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 LM3424, LM3424-Q1 www.ti.com SNVS603C - AUGUST 2009 - REVISED AUGUST 2015 11 Device and Documentation Support 11.1 Device Support 11.1.1 Third-Party Products Disclaimer TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE. 11.2 Related Links The table below lists quick access links. Categories include technical documents, support and community resources, tools and software, and quick access to sample or buy. Table 9. Related Links PARTS PRODUCT FOLDER SAMPLE & BUY TECHNICAL DOCUMENTS TOOLS & SOFTWARE SUPPORT & COMMUNITY LM3424 Click here Click here Click here Click here Click here LM3424-Q1 Click here Click here Click here Click here Click here 11.3 Community Resources The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of Use. TI E2ETM Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help solve problems with fellow engineers. Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and contact information for technical support. 11.4 Trademarks PowerPAD, E2E are trademarks of Texas Instruments. All other trademarks are the property of their respective owners. 11.5 Electrostatic Discharge Caution These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. 11.6 Glossary SLYZ022 -- TI Glossary. This glossary lists and explains terms, acronyms, and definitions. 12 Mechanical, Packaging, and Orderable Information The following pages include mechanical, packaging, and orderable information. This information is the most current data available for the designated devices. This data is subject to change without notice and revision of this document. For browser-based versions of this data sheet, refer to the left-hand navigation. Copyright (c) 2009-2015, Texas Instruments Incorporated Product Folder Links: LM3424 LM3424-Q1 Submit Documentation Feedback 63 PACKAGE OPTION ADDENDUM www.ti.com 21-Mar-2016 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan Lead/Ball Finish MSL Peak Temp (2) (6) (3) Op Temp (C) Device Marking (4/5) LM3424MH/NOPB ACTIVE HTSSOP PWP 20 73 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 LM3424 MH LM3424MHX/NOPB ACTIVE HTSSOP PWP 20 2500 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 LM3424 MH LM3424QMH/NOPB ACTIVE HTSSOP PWP 20 73 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 LM3424 QMH LM3424QMHX/NOPB ACTIVE HTSSOP PWP 20 2500 Green (RoHS & no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 125 LM3424 QMH (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. (4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device. (5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation of the previous line and the two combined represent the entire Device Marking for that device. (6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish value exceeds the maximum column width. Addendum-Page 1 Samples PACKAGE OPTION ADDENDUM www.ti.com 21-Mar-2016 Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. 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