TPS40054 TPS40055 TPS40057 8 www.ti.com SLUS593H - DECEMBER 2003 - REVISED JULY 2012 WIDE-INPUT SYNCHRONOUS BUCK CONTROLLER Check for Samples: TPS40054, TPS40055, TPS40057 FEATURES CONTENTS 1 * * * * 2 * * * * * * * * * Operating Input Voltage 8 V to 40 V Input Voltage Feed-Forward Compensation < 1 % Internal 0.7-V Reference Programmable Fixed-Frequency Up to 1-MHz Voltage Mode Controller Internal Gate Drive Outputs for High-Side and Synchronous N-Channel MOSFETs 16-Pin PowerPADTM Package (JC = 2C/W) Thermal Shutdown Externally Synchronizable Programmable High-Side Sense Short-Circuit Protection Programmable Closed-Loop Soft-Start TPS40054 Source Only TPS40055 Source/Sink TPS40057 Source/Sink With VO Prebias Electrical Characteristics 3 Pin Descriptions 5 Application Information 7 Design Examples 22 Additional References 27 The TPS4005x is a family of high-voltage, wide input (8 V to 40 V), synchronous, step-down controllers. The TPS4005x family offers design flexibility with a variety of user-programmable functions, including soft-start, UVLO, operating frequency, voltage feedforward, high-side current limit, and loop compensation. The TPS4005x uses voltage feed-forward control techniques to provide good line regulation over the wide (4:1) input voltage range, and fast response to input line transients. Near-constant modulator gain with input variation eases loop compensation. The externally programmable current limit provides pulseby-pulse current limit, as well as hiccup mode operation utilizing an internal fault counter for longer duration overloads. Power Modules Networking/Telecom Industrial/Servers TPS4005xPWP 1 KFF ILIM 16 + 2 RT VIN - 2 DESCRIPTION APPLICATIONS * * * Device Ratings 3 BP5 VIN 15 BOOST 14 4 SYNC HDRV 13 5 SGND SW 12 6 SS/SD BP10 11 7 VFB LDRV 10 8 COMP PGND + VO - 9 UDG-03179 1 2 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. PowerPAD is a trademark of Texas Instruments. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright (c) 2003-2012, Texas Instruments Incorporated TPS40054 TPS40055 TPS40057 SLUS593H - DECEMBER 2003 - REVISED JULY 2012 www.ti.com 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. ORDERING INFORMATION TA PACKAGE APPLICATION Source -40C to 85C Plastic HTSSOP (PWP) Source/Sink Source/Sink with prebias OUTPUT SUPPLY MINIMUM QUANTITY Tube 90 DEVICE NUMBER TPS40054PWP Tape and Reel 2000 TPS40054PWPR Tube 90 TPS40055PWP Tape and Reel 2000 TPS40055PWPR Tube 90 TPS40057PWP Tape and Reel 2000 TPS40057PWPR DEVICE RATINGS ABSOLUTE MAXIMUM RATINGS over operating free-air temperature range unless otherwise noted (1) TPS40054 TPS40055 TPS40057 VIN Input voltage range VFB, SS/SD, SYNC -0.3 to 6 VIN, SW -0.3 to 45 SW, transient < 50 ns -2.5 SW, transient < 50 ns, VVIN < 14 V -5.0 KFF, with IIN(max) = - 5 mA -0.3 to 11 -0.3 to 6 VO Output voltage range COMP, RT, SS/SD IO Output current RT TJ Maximum junction temperature TJ Operating junction temperature range -40 to 125 Tstg Storage temperature -55 to 150 (1) (2) KFF (2) UNIT 5 mA 200 A 150 C Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under "recommended operating conditions" is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability. Device may shut down at junction temperatures below 150C RECOMMENDED OPERATING CONDITIONS MIN VIN Input voltage TA Operating free-air temperature NOM MAX UNIT 8 40 V -40 85 C THERMAL INFORMATION THERMAL METRIC (1) PWP (20 PINS) JA Junction-to-ambient thermal resistance 38.3 JCtop Junction-to-case (top) thermal resistance 28.0 JB Junction-to-board thermal resistance 9.0 JT Junction-to-top characterization parameter 0.4 JB Junction-to-board characterization parameter 8.9 JCbot Junction-to-case (bottom) thermal resistance 2.9 (1) 2 UNITS C/W For more information about traditional and new thermal metrics, see the IC Package Thermal Metrics application report, SPRA953. Submit Documentation Feedback Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 TPS40054 TPS40055 TPS40057 www.ti.com SLUS593H - DECEMBER 2003 - REVISED JULY 2012 ELECTRICAL CHARACTERISTICS TA = -40C to 85C, VIN = 24 Vdc, RT = 90.9 k, IKFF = 150 A, fSW = 500 kHz, all parameters at zero power dissipation (unless otherwise noted) PARAMETER TEST CONDITIONS MIN TYP MAX UNIT INPUT SUPPLY VIN Input voltage range, VIN 8 40 V 1.5 3.0 mA OPERATING CURRENT IDD Quiescent current Output drivers not switching, VFB 0.75 V Output voltage IO 1 mA 4.7 5.0 5.2 V 8 V VIN 40 V 470 520 570 kHz BP5 VBP5 OSCILLATOR/RAMP GENERATOR fOSC Accuracy (1) VRAMP PWM ramp voltage VIH High-level input voltage, SYNC VIL Low-level input voltage, SYNC ISYNC Input current, SYNC VPEAK - VVAL Pulse width, SYNC VRT 2.38 Maximum duty cycle IKFF 0.8 V 5 10 A 2.50 2.58 VFB = 0 V, fSW 500 kHz 85% VFB = 0 V, 500 kHz fSW 1 MHz (1) 80% ns Feed-forward voltage 0% 3.35 Feed-forward current operating range (1) (2) V 94% VFB 0.75 V Minumum duty cycle VKFF V 50 RT voltage DMAX 2.0 2 3.48 20 3.65 V 1100 A 2.95 A SOFT START ISS/SD Soft-start source current 1.65 2.35 VSS/SD Soft-start clamp voltage tDSCH Discharge time CSS/SD = 220 pF 1.6 2.2 2.8 tSS/SD Soft-start time CSS/SD = 220 pF, 0 V VSS/SD 1.6 V 115 150 215 Output voltage IO 1 mA 9.0 9.6 10.3 8 V VIN 40 V, TA = 25C 0.698 0.700 0.704 8 V VIN 40 V, 0C TA 85C 0.693 0.700 0.707 8 V VIN 40 V, -40C TA 85C 0.693 0.700 0.715 3.0 5.0 MHz dB 3.7 V s BP10 VBP10 V ERROR AMPLIFIER VFB Feedback input voltage GBW Gain bandwidth (1) AVOL Open loop gain 60 80 IOH High-level output source current 2.0 4.0 IOL Low-level output sink current 2.0 4.0 VOH High-level output voltage ISOURCE = 500 A 3.2 3.5 VOL Low-level output voltage ISINK = 500 A 0.20 0.35 IBIAS Input bias current VFB = 0.7 V 100 200 (1) (2) V mA V nA Ensured by design. Not production tested. IKFF increases with SYNC frequency, maximum duty cycle decreases with IKFF. Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 Submit Documentation Feedback 3 TPS40054 TPS40055 TPS40057 SLUS593H - DECEMBER 2003 - REVISED JULY 2012 www.ti.com ELECTRICAL CHARACTERISTICS (continued) TA = -40C to 85C, VIN = 24 Vdc, RT = 90.9 k, IKFF = 150 A, fSW = 500 kHz, all parameters at zero power dissipation (unless otherwise noted) PARAMETER TEST CONDITIONS MIN TYP MAX UNIT 8.5 10.0 11.5 A CURRENT LIMIT ISINK Current limit sink current VILIM = 23.7 V, VSW = (VILIM - 0.5 V) Propagation delay to output VILIM = 23.7 V, VSW = (VILIM - 2 V) tON Switch leading-edge blanking pulse time (3) tOFF Off time during a fault (soft-start cycle time) Offset voltage SW vs. ILIM 200 ns 100 7 TA = 25C VOS 300 -90 -70 cycles -50 VILIM = 23.6 V, 0C TA 85C -120 -38 VILIM = 23.6 V, -40C TA 85C -120 -20 mV OUTPUT DRIVER tLRISE Low-side driver rise time tLFALL Low-side driver fall time tHRISE High-side driver rise time tHFALL High-side driver fall time CLOAD = 2200 pF CLOAD = 2200 pF (HDRV - SW) VOH High-level ouput voltage, HDRV IHDRV = -0.1 A (HDRV - SW) VOL Low-level ouput voltage, HDRV IHDRV = 0.1 A (HDRV - SW) VOH High-level ouput voltage, LDRV ILDRV = -0.1 A VOL Low-level ouput voltage, LDRV ILDRV = 0.1 A 48 96 24 48 48 96 36 72 VBOOST -1.5 V VBOOST -1.0 V VBP10 -1.4 V VBP10 - 1.0 V 0.75 ns V 0.5 Minimum controllable pulse width 100 150 ns SS/SD SHUTDOWN VSD Shutdown threshold voltage VEN Device active threshold voltage Outputs off 90 125 160 190 210 245 31.2 32.2 33.5 -10 -5 0 mV 25 A mV BOOST REGULATOR VBOOST Output voltage VIN= 24.0 V V RECTIFIER ZERO CURRENT COMPARATOR (TPS40054 ONLY) VSW Switch voltage LDRV output OFF SW NODE ILEAK Leakage current (3) (out of pin) THERMAL SHUTDOWN Shutdown temperature (3) TSD Hysteresis 165 (3) C 20 UVLO VUVLO KFF programmable threshold voltage VDD UVLO, fixed VDD UVLO, hysteresis (3) 4 RKFF = 28.7 k 6.95 7.2 7.50 7.95 7.5 7.9 V 0.46 Ensured by design. Not production tested. Submit Documentation Feedback Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 TPS40054 TPS40055 TPS40057 www.ti.com SLUS593H - DECEMBER 2003 - REVISED JULY 2012 Table 1. PIN DESCRIPTIONS TERMINAL I/O DESCRIPTION NAME NO. BOOST 14 O Gate drive voltage for the high side N-channel MOSFET. The BOOST voltage is 9 V greater than the SW voltage. A 0.1-F ceramic capacitor should be connected from this pin to the drain of the lower MOSFET. BP5 3 O 5-V reference. This pin should be bypassed to ground with a 0.1-F ceramic capacitor. This pin may be used with an external DC load of 1 mA or less. BP10 11 O 10-V reference used for gate drive of the N-channel synchronous rectifier. This pin should be bypassed by a 1-F ceramic capacitor. This pin may be used with an external DC load of 1 mA or less. COMP 8 O Output of the error amplifier, input to the PWM comparator. A feedback network is connected from this pin to the VFB pin to compensate the overall loop. The comp pin is internally clamped above the peak of the ramp to improve large signal transient response. HDRV 13 O Floating gate drive for the high-side N-channel MOSFET. This pin switches from BOOST (MOSFET on) to SW (MOSFET off). ILIM 16 I Current limit pin, used to set the overcurrent threshold. An internal current sink from this pin to ground sets a voltage drop across an external resistor connected from this pin to VCC. The voltage on this pin is compared to the voltage drop (VIN - SW) across the high-side MOSFET during conduction. KFF 1 I A resistor is connected from this pin to VIN to program the amount of voltage feed-forward and UVLO level. The current fed into this pin is internally divided and used to control the slope of the PWM ramp. LDRV 10 O Gate drive for the N-channel synchronous rectifier. This pin switches from BP10 (MOSFET on) to ground (MOSFET off). PGND 9 RT 2 SGND 5 Signal ground reference for the device. SS/SD 6 I Soft-start programming and shutdown pin. A capacitor connected from this pin to ground programs the soft-start time. The capacitor is charged with an internal current source of 2.3 A. The resulting voltage ramp on the SS/SD pin is used as a second non-inverting input to the error amplifier. The output voltage begins to rise when VSS/SD is approximately 0.85 V. The output continues to rise and reaches regulation when VSS/SD is approximately 1.55 V. The controller is considered shut down when VSS/SD is 125 mV or less. The internal circuitry is enabled when VSS/SD is 210 mV or greater. When VSS/SD is less than approximately 0.85 V, the outputs cease switching and the output voltage (VO) decays while the internal circuitry remains active. SW 12 I This pin is connected to the switched node of the converter and used for overcurrent sensing. The TPS40054 also uses this pin for zero current sensing. SYNC 4 I Syncronization input for the device. This pin can be used to synchronize the oscillator to an external master frequency. If synchronization is not used, connect this pin to SGND. VFB 7 I Inverting input to the error amplifier. In normal operation the voltage on this pin is equal to the internal reference voltage, 0.7 V. VIN 15 I Supply voltage for the device. Power ground reference for the device. There should be a low-impedance path from this pin to the source(s) of the lower MOSFET(s). I A resistor is connected from this pin to ground to set the internal oscillator and switching frequency. PWP PACKAGE (TOP VIEW) KFF 1 16 ILIM RT 2 15 VIN BP5 3 14 BOOST SYNC 4 13 HDRV SGND 5 12 SW SS/SD 6 11 BP10 VFB 7 10 LDRV COMP 8 9 PGND Thermal Pad A. For more information on the PWP package, refer to TI Technical Brief, Literature No. SLMA002. B. PowerPADTM heat slug must be connected to SGND (pin 5) or electrically isolated from all other pins. Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 Submit Documentation Feedback 5 TPS40054 TPS40055 TPS40057 SLUS593H - DECEMBER 2003 - REVISED JULY 2012 www.ti.com SIMPLIFIED BLOCK DIAGRAM ILIM 16 BP10 VIN 15 11 BP10 14 BOOST CLK RT 2 SYNC 4 CLK Oscillator + 10V Regulator 7 1V5REF Ramp Generator 07VREF KFF 1 1V5REF Reference Voltages 3V5REF 3-bit up/down Fault Counter 7 N-channel Driver 7 Restart Fault 7 12 SW 07VREF VFB 7 7 Soft Start SS/SD 13 HDRV 7 7 BP5 BP5 7 CL 7 7 BP5 3 7 CLK + + 6 7 BP10 7 Fault 7 S Q R Q CL N-channel Driver 10 LDRV 9 PGND tSTART 7 Overtemperature COMP Restart 7 7 8 5 SW S CLK R Q Zero Current Detector (TPS40054 Only) UDG-08118 SGND 6 Submit Documentation Feedback Q Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 TPS40054 TPS40055 TPS40057 www.ti.com SLUS593H - DECEMBER 2003 - REVISED JULY 2012 APPLICATION INFORMATION The TPS40054/55/57 family of devices allows the user to optimize the PWM controller to the specific application. The TPS40057 is safe for pre-biased outputs, not turning on the synchronous rectifier until the high-side FET has already started switching. The TPS40054 operates in one quadrant and sources output current only, allowing for paralleling of converters and ensures that one converter does not sink current from another converter. This controller also emulates a non-synchronous buck converter at light loads where the inductor current goes discontinuous. At continuous output inductor currents the controller operates as a synchronous buck converter to optimize efficiency. The TPS40055 operates in two quadrants, sourcing and sinking output current. SETTING THE SWITCHING FREQUENCY (PROGRAMMING THE CLOCK OSCILLATOR) The TPS4005x has independent clock oscillator and ramp generator circuits. The clock oscillator serves as the master clock to the ramp generator circuit. The switching frequency, fSW in kHz, of the clock oscillator is set by a single resistor (RT) to ground. The clock frequency is related to RT, in k by Equation 1 and the relationship is charted in Figure 2. RT + f SW 1 17.82 10 *6 * 17 kW (1) PROGRAMMING THE RAMP GENERATOR CIRCUIT The ramp generator circuit provides the actual ramp used by the PWM comparator. The ramp generator provides voltage feed-forward control by varying the PWM ramp slope with line voltage, while maintaining a constant ramp magnitude. Varying the PWM ramp directly with line voltage provides excellent response to line variations since the PWM does not have to wait for loop delays before changing the duty cycle. (See Figure 1). VIN SW VPEAK COMP RAMP VVALLEY t1 tON1 tON2 t2 tON D= t tON1 > tON2 and D1 > D2 UDG-08119 Figure 1. Voltage Feed-Forward Effect on PWM Duty Cycle The PWM ramp must be faster than the master clock frequency or the PWM is prevented from starting. The PWM ramp time is programmed via a single resistor (RKFF) pulled up to VIN. RKFF is related to RT, and the minimum input voltage, VIN(min) through the following: ( ) RKFF = VIN(min) - VKFF (58.14 RT + 1340 ) W where * * VIN(min) is the ensured minimum start-up voltage (the actual start-up voltage is nominally about 10% lower at 25C) RT is the timing resistance in k Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 Submit Documentation Feedback 7 TPS40054 TPS40055 TPS40057 SLUS593H - DECEMBER 2003 - REVISED JULY 2012 * www.ti.com VKFF is the voltage at the KFF pin (typical value is 3.48 V) (2) The curve showing the RKFF required for a given switching frequency, fSW, and VUVLO is shown in Figure 3. For low-input voltage and high duty-cycle applications, the voltage feed-forward may limit the duty cycle prematurely. This does not occur for most applications. The voltage control loop controls the duty cycle and regulates the output voltage. For more information on large duty cycle operation, refer to Application Note (SLUA310), Effect of Programmable UVLO on Maximum Duty Cycle. FEED-FORWARD IMPEDANCE vs SWITCHING FREQUENCY 600 700 500 600 RKFF - Feed-Forward Impedance - k RT - Timing Resistance - k SWITCHING FREQUENCY vs TIMING RESISTANCE 400 300 200 100 500 400 VIN = 9 V 300 VIN = 15 V VIN = 25 V 200 100 0 100 200 300 400 500 600 700 800 fSW - Switching Frequency - kHz 900 1000 0 100 200 300 400 500 600 700 800 900 1000 fSW - Switching Frequency - kHz Figure 2. Figure 3. UVLO OPERATION The TPS4005x uses variable (user-programmable) UVLO protection. See the Programming the Ramp Generator section for more information on setting the UVLO voltage. The UVLO circuit holds the soft-start low until the input voltage has exceeded the user-programmable undervoltage threshold. The TPS4005x uses the feed-forward pin, KFF, as a user-programmable low-line UVLO detection. This variable low-line UVLO threshold compares the PWM ramp duration to the oscillator clock period. An undervoltage condition exists if the TPS4005x receives a clock pulse before the ramp has reached 90% of its full amplitude. The ramp duration is a function of the ramp slope, which is directly related to the current into the KFF pin. The KFF current is a function of the input voltage and the resistance from KFF to the input voltage. The KFF resistor can be referenced to the oscillator frequency as descibed in Equation 2. The programmable UVLO function uses a three-bit counter to prevent spurious shut-downs or turn-ons due to spikes or fast line transients. When the counter reaches a total of seven counts in which the ramp duration is shorter than the clock cycle, a powergood signal is asserted and a soft-start initiated, and the upper and lower MOSFETS are turned off. Once the soft-start is initiated, the UVLO circuit must see a total count of seven cycles in which the ramp duration is longer than the clock cycle before an undervoltage condition is declared. (See Figure 4). 8 Submit Documentation Feedback Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 TPS40054 TPS40055 TPS40057 www.ti.com SLUS593H - DECEMBER 2003 - REVISED JULY 2012 UVLO Threshold VIN Clock PWM RAMP 1 2 3 4 5 6 7 1 2 1 2 3 4 5 6 7 PowerGood UDG-02132 Figure 4. Undervoltage Lockout Operation The tolerance on the UVLO set point also affects the maximum duty cycle achievable. If the UVLO starts the device at 10% below the nominal start-up voltage, the maximum duty cycle is reduced approximately 10% at the nominal start-up voltage. The impedance of the input voltage can cause the input voltage, at the controller, to sag when the converter starts to operate and draw current from the input source. Therefore, there is voltage hysteresis that prevents nuisance shutdowns at the UVLO point. With RT chosen to select the operating frequency and RKFF chosen to select the start-up voltage, the approximate amount of hysteresis voltage is shown in Figure 5. UNDERVOLTAGE LOCKOUT THRESHOLD vs HSYTERESIS 1.2 VUVLO - Hysteresis - V 1.0 0.8 0.6 0.4 0.2 0 10 15 20 25 30 35 40 VUVLO - Undervoltage Lockout Threshold - V Figure 5. Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 Submit Documentation Feedback 9 TPS40054 TPS40055 TPS40057 SLUS593H - DECEMBER 2003 - REVISED JULY 2012 www.ti.com Some applications may require an additional circuit to prevent false restarts at the UVLO voltage level. This applies to applications which have high impedance on the input voltage line or which have excessive ringing on the VIN line. The input voltage impedance can cause the input voltage to sag enough at start up to cause a UVLO shutdown and subsequent restart. Excessive ringing can also affect the voltage seen by the device and cause a UVLO shutdown and restart. A simple external circuit provides a selectable amount of hysteresis to prevent the nuisance UVLO shutdown. Assuming a hysteresis current of 10% IKFF, and the peak detector charges to 8 V and VIN(min) = 10 V, the value of RA is calculated by Equation 3 using a RKFF = 71.5 k. RA = RKFF (8 - 3.48 ) ( 0.1 VIN(min ) - 3.48 = 495kW = 499kW ) (3) CA is chosen to maintain the peak voltage between switching cycles in order to keep the capacitor charge from drooping 0.1 V (from 8 V to 7.9 V). CA = (8 - 3.48 ) (R A 7.9 fSW ) (4) The value of CA may calculate to less than 10 pF, but some standard value up to 47 pF works adequately. The diode can be a small-signal switching diode or Schottky rated for more then 20 V. Figure 6 illustrates a typical implementation using a small switching diode. The tolerance on the UVLO set point also affects the maximum duty cycle achievable. If the UVLO starts the device at 10% below the nominal start-up voltage, the maximum duty cycle is reduced approximately 10% at the nominal start up voltage. RA 499 kW CA 47 pF TPS4005xPWP RKFF 71.5 kW 1 KFF ILIM 16 2 RT VIN 15 3 BP5 4 SYNC HDRV 13 5 SGND SW 12 6 SS BP10 11 7 VFB LDRV 10 8 COMP PGND BOOST 14 DA 1N914, 1N4150 Type Signal Diode 9 PGND UDG-08102 Figure 6. Hysteresis for Programmable UVLO 10 Submit Documentation Feedback Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 TPS40054 TPS40055 TPS40057 www.ti.com SLUS593H - DECEMBER 2003 - REVISED JULY 2012 BP5 AND BP10 INTERNAL VOLTAGE REGULATORS Start-up characteristics of the BP5 and BP10 regulators over different temperature ranges are shown in Figure 7 and Figure 8. Slight variations in the BP5 occurs dependent upon the switching frequency. Variation in the BP10 regulation characteristics is also based on the load presented by switching the external MOSFETs. INPUT VOLTAGE vs BP5 VOLTAGE INPUT VOLTAGE vs BP10 VOLTAGE 6 10 9 110C 8 VBP10 - BP10 Voltage - V VBP5 - BP5 Voltage - V 5 25C 4 - 55C 3 2 110C 7 6 5 25C 4 3 2 - 55C 1 1 0 2 4 6 8 10 VIN - Input Voltage - V 12 2 4 6 8 10 12 VIN - Input Voltage - V Figure 7. Figure 8. SELECTING THE INDUCTOR VALUE The inductor value determines the magnitude of ripple current in the output capacitors as well as the load current at which the converter enters discontinuous mode. Too large an inductance results in lower ripple current but is physically larger for the same load current. Too small an inductance results in larger ripple currents and a greater number of (or more expensive output capacitors for) the same output ripple voltage requirement. A good compromise is to select the inductance value such that the converter doesn't enter discontinuous mode until the load approximated somewhere between 10% and 30% of the rated output. The inductance value is described in Equation 5. L+ V IN * V O VIN DI VO f SW (Henries) where * * VO is the output voltage I is the peak-to-peak inductor current Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 (5) Submit Documentation Feedback 11 TPS40054 TPS40055 TPS40057 SLUS593H - DECEMBER 2003 - REVISED JULY 2012 www.ti.com CALCULATING THE OUTPUT CAPACITANCE The output capacitance depends on the output ripple voltage requirement, output ripple current, as well as any output voltage deviation requirement during a load transient. The output ripple voltage is a function of both the output capacitance and capacitor ESR. The worst-case output ripple is described in Equation 6. ae ae oo 1 D V = D I c ESR + c / // c e 8 CO fSW o o e where * * CO is the output capacitance ESR is the equivalent series resistance of the output capacitance (6) The output ripple voltage is typically between 90% and 95% due to the ESR component. The output capacitance requirement typically increases in the presence of a load transient requirement. During a step load, the output capacitance must provide energy to the load (light to heavy load step) or absorb excess inductor energy (heavy to light load step) while maintaining the output voltage within acceptable limits. The amount of capacitance depends on the magnitude of the load step, the speed of the loop and the size of the inductor. Stepping the load from a heavy load to a light load results in an output overshoot. Excess energy stored in the inductor must be absorbed by the output capacitance. The energy stored in the inductor is described in Equation 7. E L + 1 L I 2 (Joules) 2 (7) where I2 + I 2 OH * * * I OL 2 (Amperes)2 IOH is the output current under heavy load conditions IOL is the output current under light load conditions (8) Energy in the capacitor is described in Equation 9. E C + 1 C V2 (Joules) 2 (9) where V2 + V * V 2 2 f Volts2 i where * * Vf is the final peak capacitor voltage Vi is the initial capacitor voltage (10) Substituting Equation 8 into Equation 7, then substituting Equation 10 into Equation 9, then setting Equation 9 equal to Equation 7, and then solving for CO yields the capacitance described in Equation 11. L CO + I * I V * V 2 OL 2 f 12 2 OH (Farads) 2 i Submit Documentation Feedback (11) Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 TPS40054 TPS40055 TPS40057 www.ti.com SLUS593H - DECEMBER 2003 - REVISED JULY 2012 PROGRAMMING SOFT START The TPS4005x uses a closed-loop soft-start system to ensure a controlled ramp of the output during startup. The reference voltage used for the startup is derived in the following manner. A capacitor (CSS/SD) is connected to the SS/SD pin. There is a ramped voltage generated at this pin by charging CSS/SD with a current source. A value of 0.85 V is subtracted from the voltage at the SS/SSD pin and is applied to a non-inverting input of the error amplifier. This is the effective soft-start ramp voltage, VSSRMP. The error amplifier also has the 0.7-V reference (VFB) voltage applied to a non-inverting input. The structure of the error amplifier input stage is such that the lower of VFB or VSSRMP becomes the dominant voltage that the error amplifier uses to regulate the FB pin. This provides a clean, closed-loop startup while VSSRMP is lower than VFB and a precision reference regulated supply as VSSRMP climbs above VFB. To ensure a controlled ramp-up of the output voltage, the soft-start time should be greater than the L-CO time constant as described in Equation 12. t START w 2p L CO (seconds) where * tSTART is the startup ramp time in s (12) There is a direct correlation between tSTART and the input current required during start-up. The faster tSTART, the higher the input current required during start-up. This relationship is described in more detail in the section titled, Programming the Current Limit which follows. The soft-start capacitance, CSS/SD, is described in Equation 13. For applications in which the VIN supply ramps up slowly (typically between 50 ms and 100 ms), it may be necessary to increase the soft-start time to between approximately 2 ms and 5 ms to prevent nuisance UVLO tripping. The soft-start time should be longer than the time that the VIN supply transitions between 6 V and 7 V. aeI o C SS / SD = c SS / SD / t START (F ) V FB o e where * * ISS/SD is the soft-start charge current (typical value is 2.35 A) VFB is the feedback reference voltage (typical value is 0.7 V) Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 (13) Submit Documentation Feedback 13 TPS40054 TPS40055 TPS40057 SLUS593H - DECEMBER 2003 - REVISED JULY 2012 www.ti.com PROGRAMMING CURRENT LIMIT The TPS4005x uses a two-tier approach for overcurrent protection. The first tier is a pulse-by-pulse protection scheme. Current limit is implemented on the high-side MOSFET by sensing the voltage drop across the MOSFET when the gate is driven high. The MOSFET voltage is compared to the voltage dropped across a resistor connected from VIN pin to the ILIM pin when driven by a constant current sink. If the voltage drop across the MOSFET exceeds the voltage drop across the ILIM resistor, the switching pulse is immediately terminated. The MOSFET remains off until the next switching cycle is initiated. The second tier consists of a fault counter. The fault counter is incremented on an overcurrent pulse and decremented on a clock cycle without an overcurrent pulse. When the counter reaches seven (7) a restart is issued and seven soft-start cycles are initiated. Both the upper and lower MOSFETs are turned off during this period. The counter is decremented on each soft-start cycle. When the counter is decremented to zero, the PWM is re-enabled. If the fault has been removed the output starts up normally. If the output is still present the counter counts seven overcurrent pulses and re-enters the second-tier fault mode. See Figure 9 for typical overcurrent protection waveforms. The minimum current limit setpoint (IILIM) is calculated in Equation 14. ae C VO o IILIM = c O / + ILOAD (A ) e tSTART o where * ILOAD is the load current at start-up (14) HDRV CLOCK tBLANKING VILIM VVIN-VSW SS 7 CURRENT LIMIT TRIPS (HDRV CYCLE TERMINATED BY CURRENT LIMIT TRIP) 7 SOFT-START CYCLES UDG-02136 Figure 9. Typical Current Limit Protection Waveforms 14 Submit Documentation Feedback Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 TPS40054 TPS40055 TPS40057 www.ti.com SLUS593H - DECEMBER 2003 - REVISED JULY 2012 The current limit programming resistor (RILIM) is calculated using Equation 15. Care must be taken in choosing the values used for VOS and ISINK in the equation. In order to ensure the output current at the overcurrent level, the minimum value of ISINK and the maximum value of VOS must be used. The main purpose is hard fault protection of the power switches. RILIM = IOC RDS(on )emax u + VOS e u 1.12 ISINK + 42.86 10-3 (W ) ISINK where * * * ISINK is the current into the ILIM pin and is 8.5 A, minimum IOC is the overcurrent setpoint which is the DC output current plus one-half of the peak inductor current VOS is the overcurrent comparator offset and is -20 mV, maximum (15) SYNCHRONIZING TO AN EXTERNAL SUPPLY The TPS4005x can be synchronized to an external clock through the SYNC pin. Synchronization occurs on the falling edge of the SYNC signal. The synchronization frequency should be in the range of 20% to 30% higher than its programmed free-run frequency. The clock frequency at the SYNC pin replaces the master clock generated by the oscillator circuit. Pulling the SYNC pin low programs the TPS4005x to freely run at the frequency programmed by RT. The higher synchronization must be factored in when programming the PWM ramp generator circuit. If the PWM ramp is interrupted by the SYNC pulse, a UVLO condition is declared and the PWM becomes disabled. Typically this is of concern under low-line conditions only. In any case, RKFF needs to be adjusted for the higher switching frequency. In order to specify the correct value for RKFF at the synchronizing frequency, calculate a dummy value for RT that would cause the oscillator to run at the synchronizing frequency. Do not use this value of RT in the design. ae o 1 RT(dummy ) = c - 17 / (kW ) -6 cf / e SYNC 17.82 10 o where * fSYNC is the synchronizing frequency in kHz (16) Use the value of RT(dummy) to calculate the value for RKFF. ( )( ) RKFF = VIN(min ) - VKFF 58.14 RT(dummy ) + 1340 W where * RT(dummy) is in k (17) This value of RKFF ensures that UVLO is not engaged when operating at the synchronization frequency. LOOP COMPENSATION Voltage-mode buck-type converters are typically compensated using Type III networks. Since the TPS4005x uses voltage feedforward control, the gain of the PWM modulator with voltage feedforward circuit must be included. The generic modulator gain is described in Figure 10. Duty cycle, D, varies from 0 to 1 as the control voltage, VC, varies from the minimum ramp voltage to the maximum ramp voltage, VS. Also, for a synchronous buck converter, D = VO / VIN. To get the control voltage to output voltage modulator gain in terms of the input voltage and ramp voltage, V V VO V D + O + C or + IN VS V IN VS VC (18) With the voltage feedforward function, the ramp slope is proportional to the input voltage. Therefore the moderator DC gain is independent to the change of input voltage. Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 Submit Documentation Feedback 15 TPS40054 TPS40055 TPS40057 SLUS593H - DECEMBER 2003 - REVISED JULY 2012 www.ti.com For the TPS4005x, with VIN(min) being the minimum input voltage required to cause the ramp excursion to reach the maximum ramp amplitude of VRAMP, the modulator dc gain is shown in Equation 19. ae VIN(min ) o ae VIN(min ) o / or AMOD dB = 20 log c / AMOD = c ( ) c VRAMP / c VRAMP / e o e o (19) Calculate the Poles and Zeros For a buck converter using voltage mode control there is a double pole due to the output L-CO. The double pole is located at the frequency calculated in Equation 20. 1 f LC + (Hertz) 2p L CO (20) There is also a zero created by the output capacitance, CO, and its associated ESR. The ESR zero is located at the frequency calculated in Equation 21. 1 fZ + (Hertz) 2p ESR CO (21) Calculate the value of RBIAS to set the output voltage, VO. 0.7 R1 RBIAS = W VO - 0.7 (22) The maximum crossover frequency (0 dB loop gain) is set by Equation 23. f f C + SW (Hertz) 4 (23) Typically, fC is selected to be close to the midpoint between the L-CO double pole and the ESR zero. At this frequency, the control to output gain has a -2 slope (-40 dB/decade), while the Type III topology has a +1 slope (20 dB/decade), resulting in an overall closed loop -1 slope (-20 dB/decade). Figure 11 shows the modulator gain, L-C filter, output capacitor ESR zero, and the resulting response to be compensated. Modulator Gain (dB) ESR Zero, +1 VS VC D= VC/VS AMOD = VIN(min)/VRAMP Resultant, -1 L-C Filter, -2 100 Figure 10. PWM Modulator Relationships 16 Submit Documentation Feedback 1k 10 k Switching Frequency (Hz) 100 k Figure 11. Modulator Gain vs Switching Frequency Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 TPS40054 TPS40055 TPS40057 www.ti.com SLUS593H - DECEMBER 2003 - REVISED JULY 2012 A Type III topology, shown in Figure 12, has two zero-pole pairs in addition to a pole at the origin. The gain and phase boost of a Type III topology is shown in Figure 13. The two zeros are used to compensate the L-CO double pole and provide phase boost. The double pole is used to compensate for the ESR zero and provide controlled gain roll-off. In many cases the second pole can be eliminated and the amplifier's gain roll-off used to roll-off the overall gain at higher frequencies. C2 (optional) C1 R3 -1 +1 0 dB R2 -1 C3 VFB R1 7 VO GAIN -90 + 8 COMP 180 PHASE RBIAS -270 VREF UDG-08103 Figure 12. Type III Compensation Configuration Figure 13. Type III Compensation Gain and Phase The poles and zeros for a Type III network are described in Equation 24 through Equation 27. 1 fZ1 = (Hz ) 2p R2 C1 1 fZ2 = (Hz ) 2p R1 C3 1 fP1 = (Hz ) 2p R2 C2 1 fP2 = (Hz ) 2p R3 C3 (24) (25) (26) (27) The value of R1 is somewhat arbitrary, but influences other component values. A value between 50 k and 100 k usually yields reasonable values. The unity gain frequency is described in Equation 28. 1 fC + (Hertz) 2p R1 C2 G where * G is the reciprocal of the modulator gain at fC (28) The modulator gain as a function of frequency at fC, is described in Equation 29. aef o AMOD(f ) = AMOD c LC / e fC o 2 and G = 1 AMOD(f ) Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 (29) Submit Documentation Feedback 17 TPS40054 TPS40055 TPS40057 SLUS593H - DECEMBER 2003 - REVISED JULY 2012 www.ti.com Minimum Load Resistance Care must be taken not to load down the output of the error amplifier with the feedback resistor, R2, that is too small. The error amplifier has a finite output source and sink current which must be considered when sizing R2. Too small a value does not allow the output to swing over its full range. VC (max) R2 (MIN) + + 3.5 V + 1750 W I SOURCE (min) 2 mA (30) CALCULATING THE BOOST AND BP10 BYPASS CAPACITOR The BOOST capacitance provides a local, low impedance source for the high-side driver. The BOOST capacitor should be a good quality, high-frequency capacitor. The size of the bypass capacitor depends on the total gate charge of the MOSFET and the amount of droop allowed on the bypass capacitor. The BOOST capacitance is described in Equation 31. Qg C BOOST + (Farads) DV (31) The 10-V reference pin, BP10V provides energy for both the synchronous MOSFET and the high-side MOSFET via the BOOST capacitor. Neglecting any efficiency penalty, the BP10V capacitance is described in Equation 32. C BP10 + QgHS ) QgSR DV (Farads) (32) dv/dt INDUCED TURN-ON MOSFETs are susceptible to dv/dt turn-on particularly in high-voltage (VDS) applications. The turn-on is caused by the capacitor divider that is formed by CGD and CGS. High dv/dt conditions and drain-to-source voltage, on the MOSFET causes current flow through CGD and causes the gate-to-source voltage to rise. If the gate-to-source voltage rises above the MOSFET threshold voltage, the MOSFET turns on, resulting in large shoot-through currents. Therefore, the SR MOSFET should be chosen so that the QGD charge is smaller than the QGS charge. 18 Submit Documentation Feedback Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 TPS40054 TPS40055 TPS40057 www.ti.com SLUS593H - DECEMBER 2003 - REVISED JULY 2012 HIGH-SIDE MOSFET POWER DISSIPATION The power dissipated in the external high-side MOSFET is comprised of conduction and switching losses. The conduction losses are a function of the IRMS current through the MOSFET and the RDS(on) of the MOSFET. The high-side MOSFET conduction losses are defined by Equation 33. P COND + I RMS 2 R DS(on) 1 ) TCR T J * 25 C O (Watts) where * TCR is the temperature coefficient of the MOSFET RDS(on) (33) The TCR varies depending on MOSFET technology and manufacturer, but typically ranges between 3500 ppm/C and 7000 ppm/C. The IRMS current for the high-side MOSFET is described in Equation 34. d A I +I RMS RMS OUT (34) The switching losses for the high-side MOSFET are descibed in Equation 35. P SW(fsw) + VIN I OUT t SW f SW (Watts) where * * * IO is the DC output current tSW is the switching rise time, typically < 20 ns fSW is the switching frequency (35) Typical switching waveforms are shown in Figure 14. ID2 } IO ID1 d I 1-d BODY DIODE CONDUCTION BODY DIODE CONDUCTION SW 0 ANTI-CROSS CONDUCTION SYNCHRONOUS RECTIFIER ON HIGH SIDE ON UDG-02139 Figure 14. Inductor Current and SW Node Waveforms The maximum allowable power dissipation in the MOSFET is determined by Equation 36. PT + TJ * TA q JA (Watts) where * * PT = PCOND + PSW(fsw) (W) JA is the package thermal impedance Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 (36) Submit Documentation Feedback 19 TPS40054 TPS40055 TPS40057 SLUS593H - DECEMBER 2003 - REVISED JULY 2012 www.ti.com SYNCHRONOUS RECTIFIER MOSFET POWER DISSIPATION The power dissipated in the synchronous rectifier MOSFET is comprised of three components: RDS(on) conduction losses, body diode conduction losses, and reverse recovery losses. RDS(on) conduction losses can be defined using Equation 31 and the RMS current through the synchronous rectifier MOSFET is described in Equation 37. 1 * d Amperes I +I RMS RMS O (37) The body-diode conduction losses are due to forward conduction of the body diode during the anti-cross conduction delay time. The body diode conduction losses are described by Equation 38. P DC + 2 I O V F t DELAY f SW (Watts) where * * VF is the body diode forward voltage tDELAY is the delay time just before the SW node rises (38) The 2-multiplier is used because the body diode conducts twice during each cycle (once on the rising edge and once on the falling edge). The reverse recovery losses are due to the time it takes for the body diode to recover from a forward bias to a reverse blocking state. The reverse recovery losses are described in Equation 39. P RR + 0.5 Q RR V IN f SW (Watts) where * QRR is the reverse recovery charge of the body diode (39) The QRR is not always described in a MOSFET data sheet, but may be obtained from the MOSFET vendor. The total synchronous rectifier MOSFET power dissipation is described in Equation 40. P SR + PDC ) PRR ) PCOND (Watts) (40) TPS4005x POWER DISSIPATION The power dissipation in the TPS4005x is largely dependent on the MOSFET driver currents and the input voltage. The driver current is proportional to the total gate charge, Qg, of the external MOSFETs. Driver power (neglecting external gate resistance, ( refer to PowerPAD Thermally Enhanced Package [2] ) can be calculated from Equation 41. P D + Q g VDR f SW (Wattsdriver) (41) And the total power dissipation in the TPS4005x, assuming the same MOSFET is selected for both the high-side and synchronous rectifier, is described in Equation 42. 2 PD PT + ) IQ V IN (Watts) V DR (42) or P T + 2 Qg f SW ) I Q V IN (Watts) where * IQ is the quiescent operating current (neglecting drivers) (43) The maximum power capability of the PowerPad package is dependent on the layout as well as air flow. The thermal impedance from junction to air, assuming 2 oz. copper trace and thermal pad with solder and no air flow, q JA + 36.515OCW (44) The maximum allowable package power dissipation is related to ambient temperature by Equation 45. T * TA PT + J (Watts) q JA (45) Substituting Equation 38 into Equation 43 and solving for fSW yields the maximum operating frequency for the TPS4005x. The result is described in Equation 46. 20 Submit Documentation Feedback Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 TPS40054 TPS40055 TPS40057 www.ti.com ae ae (T - TA ) o cc J / - IQ c ce qJA VIN /o fSW = c 2 Qg c c e SLUS593H - DECEMBER 2003 - REVISED JULY 2012 o / / / / / o (Hz ) (46) LAYOUT CONSIDERATIONS MOSFET PACKAGING MOSFET package selection depends on MOSFET power dissipation and the projected operating conditions. In general, for a surface-mount applications, the DPAK style package provides the lowest thermal impedance (JA) and, therefore, the highest power dissipation capability. However, the effectiveness of the DPAK depends on proper layout and thermal management. The JA specified in the MOSFET data sheet refers to a given copper area and thickness. In most cases, a lowest thermal impedance of 40C/W requires one square inch of 2-ounce copper on a G-10/FR-4 board. Lower thermal impedances can be achieved at the expense of board area. Please refer to the selected MOSFET's data sheet for more information regarding proper mounting. GROUNDING AND CIRCUIT LAYOUT CONSIDERATIONS The TPS4005x provides separate signal ground (SGND) and power ground (PGND) pins. It is important that circuit grounds are properly separated. Each ground should consist of a plane to minimize its impedance if possible. The high power noisy circuits such as the output, synchronous rectifier, MOSFET driver decoupling capacitor (BP10), and the input capacitor should be connected to PGND plane at the input capacitor. Sensitive nodes such as the FB resistor divider, RT, and ILIM should be connected to the SGND plane. The SGND plane should only make a single point connection to the PGND plane. Component placement should ensure that bypass capacitors (BP10 and BP5) are located as close as possible to their respective power and ground pins. Also, sensitive circuits such as FB, RT and ILIM should not be located near high dv/dt nodes such as HDRV, LDRV, BOOST, and the switch node (SW). Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 Submit Documentation Feedback 21 TPS40054 TPS40055 TPS40057 SLUS593H - DECEMBER 2003 - REVISED JULY 2012 www.ti.com DESIGN EXAMPLE * * * * * * * Input voltage: 10 Vdc to 24 Vdc Output voltage: 3.3 V 2% (3.234 VO 3.366) Output current: 8 A (maximum, steady state), 10 A (surge, 10 ms duration, 10% duty cycle maximum) Output ripple: 33 mVPP at 8 A Output load response: 0.3 V 10% to 90% step load change, from 1 A to 7 A Operating temperature: -40C to 85C fSW = 300 kHz 1. Calculate maximum and minimum duty cycles DMIN = VO(min ) VIN(max ) = 3.234 = 0.135 24 DMAX = VO(max ) VIN(min ) = 3.366 = 0.337 10 (47) 2. Select switching frequency The switching frequency is based on the minimum duty cycle ratio and the propagation delay of the current limit comparator. In order to maintain current limit capability, the on time of the upper MOSFET, tON, must be greater than 300 ns (see Electrical Characteristics Table ). Therefore: aeae V oo c c O(min ) / / c c VIN max / / ae V o ae o ( )o/ c O(min ) / = c tON / or 1 = fSW = c e c / c VIN(max ) / e tSW o tSW tON e o c / c / e o (48) Using 400 ns to provide margin, f SW + 0.135 + 337 kHz 400 ns (49) Since the oscillator can vary by 10%, decrease fSW, by 10% fSW = 0.9 x 337 kHz = 303 kHz and therefore choose a frequency of 300 kHz. 3. Select I In this case I is chosen so that the converter enters discontinuous mode at 20% of nominal load. DI + I O 2 0.2 + 8 2 0.2 + 3.2 A (50) 4. Calculate the high-side MOSFET power losses Power losses in the high-side MOSFET (Si7860DP) at 24-VIN where switching losses dominate can be calculated from Equation 51. d + 8 0.135 + 2.93 A I +I RMS (51) O Substituting Equation 34 into Equation 33 yields P COND + 2.932 0.008 (1 ) 0.007 (150 * 25)) + 0.129 W (52) and from Equation 35, the switching losses can be determined. P SW(fsw) + VIN IO t SW f SW + 24 V 8A 20 ns 300 kHz + 1.152 W (53) The MOSFET junction temperature can be found by substituting Equation 52 and Equation 53 into Equation 36: T J + PCOND ) PSW 22 q JA ) T A + (0.129 ) 1.152) Submit Documentation Feedback 40 ) 85 + 136 C O (54) Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 TPS40054 TPS40055 TPS40057 www.ti.com SLUS593H - DECEMBER 2003 - REVISED JULY 2012 5. Calculate synchronous rectifier losses The synchronous rectifier MOSFET has two (2) loss components, conduction, and diode reverse recovery losses. The conduction losses are due to IRMS losses as well as body diode conduction losses during the dead time associated with the anti-cross conduction delay. The IRMS current through the synchronous rectifier from Equation 37: 1 * d + 8 1 * 0.135 + 7.44 A I +I RMS O (55) RMS The synchronous MOSFET conduction loss from Equation 33 is: PCOND = 7.442 0.008 1 + 0.007 (150 - 25 ) = 0.83 W ( ) The body diode conduction loss from Equation 38 is: P DC + 2 I O V FD t DELAY f SW + 2 8.0 A (56) 0.8 V The body diode reverse recovery loss from Equation 39 is: P RR + 0.5 Q RR V IN f SW + 0.5 30 nC 24 V 100 ns 300 kHz + 0.384 (57) 300 kHz + 0.108 W (58) The total power dissipated in the synchronous rectifier MOSFET from Equation 40 is: P SR + PRR ) PCOND ) PDC + 0.108 ) 0.83 ) 0.384 + 1.322 W (59) The junction temperature of the synchronous rectifier at 85C is: T J + PSR q JA ) T A + (1.322) 40 ) 85 + 139 oC (60) In typical applications, paralleling the synchronous rectifier MOSFET with a Schottky rectifier increases the overall converter efficiency by approximately 2% due to the lower power dissipation during the body diode conduction and reverse recovery periods. 6. Calculate the inductor value The inductor value is calculated from Equation 5. (24 * 3.3 V) 3.3 V L+ + 2.96 mH 24 V 3.2 A 300 kHz (61) A 2.9-H Coev DXM1306-2R9 or 2.6-H Panasonic ETQ-P6F2R9LFA can be used. 7. Setting the switching frequency The clock frequency is set with a resistor (RT) from the RT pin to ground. The value of RT can be found from Equation 1, with fSW in kHz. RT + f SW 1 17.82 10 *6 * 17 kW + 170 kW N use 169 kW (62) 8. Programming the ramp generator circuit The PWM ramp is programmed through a resistor (RKFF) from the KFF pin to VIN. The ramp generator also controls the input UVLO voltage. For an undervoltage level of 10 V, RKFF can be calculated from Equation 2: ( ) RKFF = VIN(min) - 3.48 (58.14 RT + 1340 ) = 72.8kW \ use 71.5kW (63) 9. Calculating the output capacitance (CO) In this example the output capacitance is determined by the load response requirement of V = 0.3 V for a 1-A to 8-A step load. CO can be calculated using Equation 11: (8 A)2 * (1 A)2 + 97 mF (3.3)2 * (3.0)2 2.9 m CO + Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 (64) Submit Documentation Feedback 23 TPS40054 TPS40055 TPS40057 SLUS593H - DECEMBER 2003 - REVISED JULY 2012 www.ti.com Using Equation 6 calculate the ESR required to meet the output ripple requirements. ae ae oo 1 33mV = 3.2 A c ESR + c / // c e 8 97 mF 300kHz o o e (65) ESR = 10.3mW - 4.3mW = 6.0mW (66) For this design example two (2) Panasonic SP EEFUEOJ1B1R capacitors, (6.3 V, 180 F, 12 m) are used. 10. Calculate the soft-start capacitor (CSS/SD) This design requires a soft-start time (tSTART) of 1 ms. CSS/SD can be calculated using Equation 13: 2.35 mA CSS / SD = 1ms = 3.36nF @ 3300pF 0.7 V (67) 11. Calculate the current limit resistor (RILIM) The current limit set point depends on tSTART, VO,CO and ILOAD at start-up as shown in Equation 14. For this design, 360 mF 3.3 V IILIM > + 8.0 A = 9.2 A 1 ms (68) For this design, add IILIM (9.2 A) to one-half the ripple current (1.6 A) and increase this value by 30% to allow for tolerances. This yields a overcurrent setpoint (IOC) of 14 A. RDS(on) is increased 30% (1.3 x 0.008) to allow for MOSFET heating. Using Equation 15 to calculate RILIM. RILIM = 14 0.0104 - 0.020 1.12 8.5 10-6 + 42.86 10-3 8.5 10-6 = 18.24kW @ 18.7kW (69) 12. Calculate loop compensation values Calculate the DC modulator gain (AMOD) from Equation 19: A MOD + 10 + 5.0 AMOD(dB) + 20 log (5) + 14 dB 2 (70) Calculate the output filter L-CO poles and COESR zeros from Equation 20 and Equation 21: 1 1 f LC + + + 4.93 kHz 2p L C O 2p 2.9 mH 360 mF (71) and fZ + 2p 1 ESR CO + 1 0.006 2p 360 mF + 73.7 kHz (72) Select the close-loop 0 dB crossover frequency, fC. For this example fC = 20 kHz. Select the double zero location for the Type III compensation network at the output filter double pole at 4.93 kHz. Select the double pole location for the Type III compensation network at the output capacitor ESR zero at 73.7 kHz. The amplifier gain at the crossover frequency of 20 kHz is determined by the reciprocal of the modulator gain AMOD at the crossover frequency from Equation 29: A MOD(f) + AMOD f LC fC 2 +5 kHz 4.93 20 kHz 2 + 0.304 (73) And also from Equation 29: 1 G+ + 1 + 3.29 0.304 A MOD(f) 24 Submit Documentation Feedback (74) Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 TPS40054 TPS40055 TPS40057 www.ti.com SLUS593H - DECEMBER 2003 - REVISED JULY 2012 Choose R1 = 100 k The poles and zeros for a type III network are described in Equation 24 through Equation 28. 1 1 f Z2 + N C3 + + 323 pF, choose 330 pF 2p R1 C3 2p 100 kW 4.93 kHz 1 1 f P2 + N R3 + + 6.55 kW, choose 6.49 kW 2p R3 C3 2p 330 pF 73.3 kHz 1 1 fC + N C2 + + 24.2 pF, choose 22 pF 2p R1 C2 G 2p 100 kW 3.29 20 kHz 1 1 f P1 + N R2 + + 98.2 kW, choose 97.6 kW 2p R2 C2 2p 22 pF 73.3 kHz 1 1 f Z1 + N C1 + + 331 pF, choose 330 pF 2p R2 C1 2p 97.6 kW 4.93 kHz Calculate the value of RBIAS from Equation 22 with R1 = 100 k. R BIAS + 0.7 V R1 + 0.7 V 100kW + 26.9 kW, choose 26.7 kW VO * 0.7 V 3.3 V * 0.7 V (75) (76) (77) (78) (79) (80) CALCULATING THE BOOST AND BP10V BYPASS CAPACITANCE The size of the bypass capacitor depends on the total gate charge of the MOSFET being used and the amount of droop allowed on the bypass capacitor. The BOOST capacitance for the Si7860DP, allowing for a 0.5 voltage droop on the BOOST pin from Equation 31 is: Qg C BOOST + + 18 nC + 36 nF DV 0.5 V (81) and the BP10V capacitance from Equation 32 is Q gHS ) Q gSR 2 Qg C BP(10 V) + + + 36 nC + 72 nF DV DV 0.5 V (82) For this application, a 0.1-F capacitor is used for the BOOST bypass capacitor and a 1.0-F capacitor is used for the BP10V bypass. DESIGN EXAMPLE SUMMARY Figure 15 shows component selection for the 10-V to 24-V to 3.3-V at 8 A dc-to-dc converter specified in the design example. For an 8-V input application, it may be necessary to add a Schottky diode from BP10 to BOOST to get sufficient gate drive for the upper MOSFET. As seen in Figure 7, the BP10 output is about 6 V with the input at 8 V so the upper MOSFET gate drive may be less than 5 V. A schottky diode is shown connected across the synchronous rectifier MOSFET as an optional device that may be required if the layout causes excessive negative SW node voltage, greater than or equal to 2 V. TPS40054-Q1, TPS40055-Q1 and TPS40057-Q1 automotive qualified versions TPS40055-EP Enhanced product 4.5 to 18V controller with power good TPS40195 4.5 to 18V controller with synchronization power good TPS40200 Wide input non-synchronous DC-DC controller Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 Submit Documentation Feedback 25 TPS40054 TPS40055 TPS40057 SLUS593H - DECEMBER 2003 - REVISED JULY 2012 www.ti.com + 330 mF 330 mF VIN RKFF 71.5 kW TPS4005xPWP - 18.7 kW 1 KFF ILIM 16 2 RT VIN 15 3 BP5 4 SYNC RT 169 kW 0.1 mF 100 pF 1.0 mF BOOST 14 22 mF 50 V 22 mF 50 V 1.0 mF 1.0 kW HDRV 13 Si7860 CSS/SD 3300 pF C1 330 pF R2 97.6 kW 5 SGND SW 12 6 SS/SD BP10 11 7 VFB LDRV 10 8 COMP C2 22 pF PGND 9 2.9 mH + R3 6.49 kW 180 mF R1 100 kW *optional Si7860 180 mF VO C3 330 pF - 1.0 mF PWP RBIAS 26.7 kW UDG-08117 Figure 15. 24-V to 3.3-V at 8-A DC-to-DC Converter Design Example 26 Submit Documentation Feedback Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 TPS40054 TPS40055 TPS40057 www.ti.com SLUS593H - DECEMBER 2003 - REVISED JULY 2012 ADDITIONAL REFERENCES RELATED DEVICES The following devices have characteristics similar to the TPS40054/5/7 and may be of interest. Table 2. RELATED DEVICES DEVICE TPS40055-EP DESCRIPTION Enhanced performance TPS40055. TPS40054-Q1 TPS40057-Q1 Automotive qualified versions of the TPS5005x series. TPS40055-Q1 TPS40192 TPS40193 TPS40200 4.5-V to 18-V Controller with Synchronization Power Good Wide-Input Non-Synchronous DC-DC Controller REFERENCES 1. Balogh, Laszlo, Design and Application Guide for High Speed MOSFET Gate Drive Circuits, Texas Instruments/Unitrode Corporation, Power Supply Design Seminar, SEM-1400 Topic 2. 2. PowerPAD Thermally Enhanced Package Texas Instruments, Semiconductor Group, Technical Brief (SLMA002) REVISION HISTORY Changes from Revision F (SEPTEMBER 2008) to Revision G Page * Deleted errors in schematic. ................................................................................................................................................. 1 * Changed ILIM to IILIM (corrected typographical error) ........................................................................................................... 14 * Added clarity to Loop Compensation section ..................................................................................................................... 15 * Changed VIN(UVLO) to VIN(min) in two places (corrected typographic errors) ......................................................................... 16 * Changed corrected Equation 46 ......................................................................................................................................... 21 * Changed corrected Equation 56 ......................................................................................................................................... 23 * Changed corrected Equation 67 ......................................................................................................................................... 24 * Changed corrected Equation 69 ......................................................................................................................................... 24 * Changed corrected reference designator values in Figure 15 ............................................................................................ 26 Changes from Revision G (SEPTEMBER 2011) to Revision H * Page Added the Thermal Information table ................................................................................................................................... 2 Copyright (c) 2003-2012, Texas Instruments Incorporated Product Folder Link(s): TPS40054 TPS40055 TPS40057 Submit Documentation Feedback 27 PACKAGE OPTION ADDENDUM www.ti.com 23-Jul-2012 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Drawing Pins Package Qty Eco Plan (2) Lead/ Ball Finish MSL Peak Temp (3) TPS40054PWP ACTIVE HTSSOP PWP 16 90 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR TPS40054PWPG4 ACTIVE HTSSOP PWP 16 90 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR TPS40054PWPR ACTIVE HTSSOP PWP 16 2000 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR TPS40054PWPRG4 ACTIVE HTSSOP PWP 16 2000 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR TPS40055PWP ACTIVE HTSSOP PWP 16 90 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR TPS40055PWPG4 ACTIVE HTSSOP PWP 16 90 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR TPS40055PWPR ACTIVE HTSSOP PWP 16 2000 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR TPS40055PWPRG4 ACTIVE HTSSOP PWP 16 2000 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR TPS40057PWP ACTIVE HTSSOP PWP 16 90 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR TPS40057PWPG4 ACTIVE HTSSOP PWP 16 90 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR TPS40057PWPR ACTIVE HTSSOP PWP 16 2000 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR TPS40057PWPRG4 ACTIVE HTSSOP PWP 16 2000 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR Samples (Requires Login) (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. Addendum-Page 1 PACKAGE OPTION ADDENDUM www.ti.com 23-Jul-2012 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. 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. TI has taken and continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release. In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis. OTHER QUALIFIED VERSIONS OF TPS40055 : * Enhanced Product: TPS40055-EP NOTE: Qualified Version Definitions: * Enhanced Product - Supports Defense, Aerospace and Medical Applications Addendum-Page 2 PACKAGE MATERIALS INFORMATION www.ti.com 23-Jul-2012 TAPE AND REEL INFORMATION *All dimensions are nominal Device Package Package Pins Type Drawing SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) B0 (mm) K0 (mm) P1 (mm) TPS40054PWPR HTSSOP PWP 16 2000 330.0 12.4 TPS40055PWPR HTSSOP PWP 16 2000 330.0 TPS40057PWPR HTSSOP PWP 16 2000 330.0 6.9 5.6 1.6 8.0 12.0 Q1 12.4 6.9 5.6 1.6 8.0 12.0 Q1 12.4 6.9 5.6 1.6 8.0 12.0 Q1 Pack Materials-Page 1 W Pin1 (mm) Quadrant PACKAGE MATERIALS INFORMATION www.ti.com 23-Jul-2012 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) TPS40054PWPR HTSSOP PWP 16 2000 367.0 367.0 35.0 TPS40055PWPR HTSSOP PWP 16 2000 367.0 367.0 35.0 TPS40057PWPR HTSSOP PWP 16 2000 367.0 367.0 35.0 Pack Materials-Page 2 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46C and to discontinue any product or service per JESD48B. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All semiconductor products (also referred to herein as "components") are sold subject to TI's terms and conditions of sale supplied at the time of order acknowledgment. TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI's terms and conditions of sale of semiconductor products. Testing and other quality control techniques are used to the extent TI deems necessary to support this warranty. Except where mandated by applicable law, testing of all parameters of each component is not necessarily performed. TI assumes no liability for applications assistance or the design of Buyers' products. Buyers are responsible for their products and applications using TI components. To minimize the risks associated with Buyers' products and applications, Buyers should provide adequate design and operating safeguards. TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other intellectual property right relating to any combination, machine, or process in which TI components or services are used. Information published by TI regarding third-party products or services does not constitute a license to use such products or services or a warranty or endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual property of the third party, or a license from TI under the patents or other intellectual property of TI. Reproduction of significant portions of TI information in TI data books or data sheets is permissible only if reproduction is without alteration and is accompanied by all associated warranties, conditions, limitations, and notices. TI is not responsible or liable for such altered documentation. Information of third parties may be subject to additional restrictions. Resale of TI components or services with statements different from or beyond the parameters stated by TI for that component or service voids all express and any implied warranties for the associated TI component or service and is an unfair and deceptive business practice. TI is not responsible or liable for any such statements. Buyer acknowledges and agrees that it is solely responsible for compliance with all legal, regulatory and safety-related requirements concerning its products, and any use of TI components in its applications, notwithstanding any applications-related information or support that may be provided by TI. Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards which anticipate dangerous consequences of failures, monitor failures and their consequences, lessen the likelihood of failures that might cause harm and take appropriate remedial actions. Buyer will fully indemnify TI and its representatives against any damages arising out of the use of any TI components in safety-critical applications. In some cases, TI components may be promoted specifically to facilitate safety-related applications. With such components, TI's goal is to help enable customers to design and create their own end-product solutions that meet applicable functional safety standards and requirements. Nonetheless, such components are subject to these terms. No TI components are authorized for use in FDA Class III (or similar life-critical medical equipment) unless authorized officers of the parties have executed a special agreement specifically governing such use. Only those TI components which TI has specifically designated as military grade or "enhanced plastic" are designed and intended for use in military/aerospace applications or environments. Buyer acknowledges and agrees that any military or aerospace use of TI components which have not been so designated is solely at the Buyer's risk, and that Buyer is solely responsible for compliance with all legal and regulatory requirements in connection with such use. TI has specifically designated certain components which meet ISO/TS16949 requirements, mainly for automotive use. Components which have not been so designated are neither designed nor intended for automotive use; and TI will not be responsible for any failure of such components to meet such requirements. Products Applications Audio www.ti.com/audio Automotive and Transportation www.ti.com/automotive Amplifiers amplifier.ti.com Communications and Telecom www.ti.com/communications Data Converters dataconverter.ti.com Computers and Peripherals www.ti.com/computers DLP(R) Products www.dlp.com Consumer Electronics www.ti.com/consumer-apps DSP dsp.ti.com Energy and Lighting www.ti.com/energy Clocks and Timers www.ti.com/clocks Industrial www.ti.com/industrial Interface interface.ti.com Medical www.ti.com/medical Logic logic.ti.com Security www.ti.com/security Power Mgmt power.ti.com Space, Avionics and Defense www.ti.com/space-avionics-defense Microcontrollers microcontroller.ti.com Video and Imaging www.ti.com/video RFID www.ti-rfid.com OMAP Mobile Processors www.ti.com/omap TI E2E Community e2e.ti.com Wireless Connectivity www.ti.com/wirelessconnectivity Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265 Copyright (c) 2012, Texas Instruments Incorporated