LT8609S 42V, 2A/3A Peak Synchronous Step-Down Regulator with 2.5A Quiescent Current FEATURES DESCRIPTION Silent Switcher(R) 2 Architecture n Ultralow EMI Emissions on Any PCB n Eliminates PCB Layout Sensitivity n Internal Bypass Capacitors Reduce Radiated EMI n Optional Spread Spectrum Modulation n Wide Input Voltage Range: 3.0V to 42V n Ultralow Quiescent Current Burst Mode(R) Operation: n <2.5A I Regulating 12V to 3.3V Q IN OUT n Output Ripple <10mV P-P n High Efficiency 2MHz Synchronous Operation: n >93% Efficiency at 1A, 12V to 5V IN OUT n 2A Maximum Continuous Output, 3A Peak Transient Output n Fast Minimum Switch-On Time: 45ns n Adjustable and Synchronizable: 200kHz to 2.2MHz n Allows Use of Small Inductors n Low Dropout n Peak Current Mode Operation n Internal Compensation n Output Soft-Start and Tracking n Small 16-Lead 3mm x 3mm LQFN Package n AEC-Q100 Qualified for Automotive Applications The LT(R)8609S is a compact, high efficiency, high speed synchronous monolithic step-down switching regulator that consumes only 1.7A of non-switching quiescent current. The LT8609S can deliver 2A of continuous current with peak loads of 3A (<1sec) to support applications such as GSM transceivers which require high transient loads. Top and bottom power switches are included with all necessary circuitry to minimize the need for external components. Low ripple Burst Mode operation enables high efficiency down to very low output currents while keeping the output ripple below 10mVP-P. A SYNC pin allows synchronization to an external clock, or spread spectrum modulation of switching frequencies for low EMI operation. Internal compensation with peak current mode topology allows the use of small inductors and results in fast transient response and good loop stability. The EN/UV pin has an accurate 1V threshold and can be used to program VIN undervoltage lockout or to shut down the LT8609S reducing the input supply current to 1A. A capacitor on the TR/SS pin programs the output voltage ramp rate during start-up while the PG flag signals when VOUT is within 8.5% of the programmed output voltage as well as fault conditions. The LT8609S is available in a small 16-lead 3mm x 3mm LQFN package. n APPLICATIONS General Purpose Step Down n Low EMI Step Down All registered trademarks and trademarks are the property of their respective owners. n TYPICAL APPLICATION 12VIN to 5VOUT Efficiency 100 5V, 2MHz Step Down 4.7F ON OFF 1F 18.2k VIN EN/UV SW SYNC LT8609S INTVCC PG TR/SS FB RT GND 90 2.2H VOUT 5V 2A 10pF 1M 22F 182k 8609S TA01a EFFICIENCY (%) VIN 5.5V TO 40V 95 85 80 75 70 65 60 55 50 fSW = 2MHz 0 0.50 1.50 1.00 IOUT (A) 2.00 2.50 8609S TA01b Rev. C Document Feedback For more information www.analog.com 1 LT8609S PIN CONFIGURATION VIN, EN/UV, PG...........................................................42V FB, TR/SS ...................................................................4V SYNC Voltage ..............................................................6V Operating Junction Temperature Range (Note 2) LT8609SE............................................... -40 to 125C LT8609SI................................................ -40 to 125C Storage Temperature Range.......................-65 to 150C Maximum Reflow (Package Body) Temperature....................................................... 260C VCC 2 GND 3 GND 4 GND FB 14 13 17 GND 5 N/C 6 7 N/C 12 PG 11 EN/UV 10 VIN 9 VIN 8 GND 1 15 N/C RT 16 SW N/C TR/SS TOP VIEW SYNC (Note 1) SW ABSOLUTE MAXIMUM RATINGS N/C LQFN PACKAGE 16-LEAD (3mm x 3mm) LQFN JEDEC BOARD: JA = 50C/W, JC(PAD) = 14C/W (NOTE 4) DEMOBOARD: JA = 31C/W EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION PART NUMBER PART MARKING* LT8609SEV#PBF LGYN LT8609SIV#PBF LGYN FINISH CODE PAD FINISH PACKAGE TYPE** MSL RATING e4 Au (RoHS) LQFN (Laminate Package with QFN Footprint 3 e4 Au (RoHS) LQFN (Laminate Package with QFN Footprint 3 TEMPERATURE RANGE -40C to 125C -40C to 125C AUTOMOTIVE PRODUCTS** LT8609SEV#WPBF LGYN LT8609SIV#WPBF LGYN -40C to 125C -40C to 125C Contact the factory for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. * Pad or ball finish code is per IPC/JEDEC J-STD-609. * Recommended PCB Assembly and Manufacturing Procedures. * Package and Tray Drawings * Parts ending with PBF are RoHS and WEEE compliant. ** The LT8609S package has the same footprint as a standard 3mm x 3mm QFN Package. **Versions of this part are available with controlled manufacturing to support the quality and reliability requirements of automotive applications. These models are designated with a #W suffix. Only the automotive grade products shown are available for use in automotive applications. Contact your local Analog Devices account representative for specific product ordering information and to obtain the specific Automotive Reliability reports for thesemodels. 2 Rev. C For more information www.analog.com LT8609S ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. PARAMETER CONDITIONS MIN TYP MAX 2.7 3.0 3.2 V l VEN/UV = 0V, VSYNC = 0V VEN/UV = 2V, Not Switching, VSYNC = 0V, VIN 36V l 1 1.7 5 12 A A VIN Current in Regulation VIN = 6V, VOUT = 2.7V, Output Load = 100A VIN = 6V, VOUT = 2.7V, Output Load = 1mA l l 46 480 90 700 A A Feedback Reference Voltage VIN = 6V, ILOAD = 100mA VIN = 6V, ILOAD = 100mA l 0.774 0.774 0.778 0.794 V V Feedback Voltage Line Regulation VIN = 4.0V to 40V l 0.02 0.06 %/V Feedback Pin Input Current VFB = 1V l 20 nA Minimum On-Time ILOAD = 1.75A, SYNC = 0V ILOAD = 1.75A, SYNC = 1.9V l l 75 60 ns ns Oscillator Frequency RT = 221k, ILOAD = 0.5A RT = 60.4k, ILOAD = 0.5A RT = 18.2k, ILOAD = 0.5A l l l Top Power NMOS On-Resistance ILOAD = 1A Minimum Input Voltage VIN Quiescent Current 0.770 0.758 45 45 Minimum Off Time 155 640 1.925 90 130 200 700 2.00 245 760 2.075 185 Top Power NMOS Current Limit l 3.4 Bottom Power NMOS On-Resistance 4.75 VIN = 42V, VSW = 40V EN/UV Pin Threshold EN/UV Rising l 0.99 EN/UV Pin Hysteresis 1.05 ns kHz kHz MHz m 5.7 115 SW Leakage Current UNITS A m 5 A 1.11 V 50 mV EN/UV Pin Current VEN/UV = 2V l 20 nA PG Upper Threshold Offset from VFB VFB Rising l 5.0 8.5 13.0 % PG Lower Threshold Offset from VFB VFB Falling l 5.0 8.5 13.0 % PG Hysteresis 0.5 PG Leakage VPG = 42V PG Pull-Down Resistance VPG = 0.1V l 550 Sync Low Input Voltage Sync High Input Voltage l INTVCC = 3.5V TR/SS Source Current Fault Condition, TR/SS = 0.1V Spread Spectrum Modulation Frequency VSYNC = 3.3V Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT8609SE is guaranteed to meet performance specifications from 0C to 125C junction temperature. Specifications over the -40C to 125C operating junction temperature range are assured by design, characterization, and correlation with statistical process controls. The LT8609SI is guaranteed over the full -40C to 125C operating junction temperature range. 1 0.5 200 nA 1200 0.9 2.7 l l TR/SS Pull-Down Resistance 0.4 % V 3.2 V 2 3 A 300 900 3 6 kHz Note 3: This IC includes overtemperature protection that is intended to protect the device during overload conditions. Junction temperature will exceed 150C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature will reduce lifetime. Note 4: values determined per JEDEC 51-7, 51-12. See the Applications Information Section for information on improving the thermal resistance and for actual temperature measurements of a demo board in typical operating conditions. Rev. C For more information www.analog.com 3 LT8609S TYPICAL PERFORMANCE CHARACTERISTICS Efficiency (3.3V Output, 2MHz, Burst Mode Operation) 100 100 95 90 VIN = 12V 70 65 60 55 50 0.0 1.0 1.5 2.0 IOUT (A) 2.5 70 50 40 30 8609S G01 VIN = 24V 60 50 40 30 20 L = 2.2H 10 0 0.001 0.01 fSW = 2MHz 0.1 1 10 IOUT (mA) 100 1k 65 10k 776.0 0.30 775.0 0.20 774.0 773.0 772.0 771.0 30 70 110 TEMPERATURE (C) -0.50 150 3.3 4.5 3.1 4.0 2.9 3.5 2.7 3.0 2.5 2.0 2.1 1.9 1.7 0.5 1.5 -0.20 4.0 0.0 8609S G07 4 10 30 20 VIN (V) 40 50 8609S G08 VIN = 12V VOUT = 3.3V 2.3 1.0 0 No-Load Supply Current vs Temperature (Not Switching) 2.5 -0.15 42.0 0.0 0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0 2.25 2.5 OUTPUT CURRENT (A) 8609S G06 No-Load Supply Current (3.3V Output) 1.5 19.2 26.8 34.4 INPUT VOLTAGE (V) 8609S G03 VIN = 12V VOUT = 3.3V 8609S G05 0.05 3 -0.20 -0.40 0.10 11.6 2.5 -0.10 769.0 5.0 -0.10 1.5 2.0 IOUT (A) 0.00 -0.30 ILOAD = 1A -0.05 1.0 0.10 770.0 8609S G04 0.00 0.5 Load Regulation 0.40 -10 fSW = 2MHz 8609S G02 777.0 768.0 -50 L = 2.2H 50 0.0 10k 0.50 IIN (A) CHANGE IN VOUT (%) 0.15 1k 70 778.0 Line Regulation 0.20 100 CHANGE IN VOUT (%) FB REGULATION VOLTAGE (mV) EFFICIENCY (%) 80 70 10 IOUT (mA) 75 FB Voltage VIN = 12V 90 1 VIN = 24V 80 55 fSW = 2MHz 0.1 85 60 L = 2.2H 0 0.001 0.01 3 Efficiency (5V Output, 2MHz, Burst Mode Operation) 100 VIN = 24V 60 10 fSW = 2MHz 0.5 90 20 L = 2.2H VIN = 12V 95 EFFICIENCY (%) EFFICIENCY (%) VIN = 24V 75 100 VIN = 12V 80 85 80 Efficiency (5V Output, 2MHz, Burst Mode Operation) INPUT CURRENT (A) 90 EFFICIENCY (%) Efficiency (3.3V Output, 2MHz, Burst Mode Operation) 1.3 -50 -10 30 70 110 TEMPERATURE (C) 150 8609S G09 Rev. C For more information www.analog.com LT8609S TYPICAL PERFORMANCE CHARACTERISTICS Top FET Current Limit vs Duty Cycle Switch Drop vs Temperature 350 5.25 4.9 300 5.00 4.8 4.75 4.7 4.50 4.25 4.6 4.5 4.00 4.4 3.75 4.3 3.50 SWITCH DROP (mV) 5.0 ISW (A) TOP FET CURRENT LIMIT (A) 5.50 Top FET Current Limit vs Temperature 0 20 40 60 DUTY CYCLE (%) 80 -10 8609S G10 30 70 110 TEMPERATURE (C) 60 MINIMUM ON-TIME (ns) 600 500 400 300 200 BOT SW 1 1.5 2 SWITCH CURRENT (A) 2.5 8609S G12 Minimum Off-Time vs Temperature 140 50 40 30 20 3 SYNC = 2V, 1.5A OUT SYNC = 0V, 1.5A OUT 0 -50 -30 -10 10 30 50 70 90 110 130 150 TEMPERATURE (C) 8609S G13 VIN = 6V ILOAD = 1A 130 120 110 100 90 80 70 60 50 -50 -30 -10 10 30 50 70 90 110 130 150 TEMPERATURE (C) 8609S G14 8609S G15 Switching Frequency vs Temperature Dropout Voltage vs Load Current 2.005 800 SWITHCING FREQUENCY (MHz) 700 600 500 400 300 200 100 0 TOP SW BOT SW 0 -50 -30 -10 10 30 50 70 90 110 130 150 TEMPERATURE (C) 150 10 100 0.5 100 150 MINIMUM OFF-TIME (ns) 700 DROPOUT VOLTAGE (mV) SWITCH DROP (mV) 70 0 150 Minimum On-Time vs Temperature 800 TOP SW 200 8609S G11 Switch Drop vs Switch Current 0 250 50 4.2 -50 100 SWITCH CURRENT = 1A 0 0.5 1 2 1.5 LOAD CURRENT (A) 2.5 3 2.000 1.995 1.990 1.985 1.980 RT = 18.2k 1.975 -50 -30 -10 10 30 50 70 90 110 130 150 TEMPERATURE (C) 8609S G16 8609S G17 Rev. C For more information www.analog.com 5 LT8609S TYPICAL PERFORMANCE CHARACTERISTICS Minimum Load to Full Frequency (SYNC Float to 1.9V) Burst Frequency vs Load Current L = 2.2H VOUT = 3.3V VIN = 12V SYNC = 0V 80 1500 1000 500 Frequency Foldback 2500 VOUT = 5V fSW = 700kHz SYNC = FLOAT 90 LOAD CURRENT (mA) 2000 FREQUENCY (kHz) 100 VIN = 12V VOUT = 3.3V SYNC = 0V RT = 18.2k 2000 70 FREQUENCY (kHz) 2500 60 50 40 30 1500 1000 20 500 10 0 0 200 400 LOAD CURRENT (mA) 0 600 0 10 30 20 INPUT VOLTAGE (V) 8609S G18 0 0.9 2.4 0.8 2.3 0.6 0.5 0.4 0.3 0.2 0.1 3.5 VSS = 0.1V 2.1 2.0 1.9 1.8 2 1.5 1.5 -50 -30 -10 10 30 50 70 90 110 130 150 TEMPERATURE (C) 0 -55 5 35 65 95 TEMPERATURE (C) 155 Switching Waveforms IL 200mA/DIV IL 500mA/DIV VSW 5V/DIV VSW 5V/DIV VSW 10V/DIV 2s/DIV 12VIN TO 5VOUT AT 25mA SYNC = 0 (Burst Mode OPERATION) 125 8609S G23 IL 500mA/DIV 6 -25 8609S G22 Switching Waveforms 8609S G24 VIN UVLO 0.5 8609S G21 200ns/DIV 12VIN TO 5VOUT AT 1A 1 1 1.7 Switching Waveforms 0.8 2.5 2.2 1.6 0.1 0.2 0.4 0.5 0.6 0.7 0.8 1.0 1.1 1.2 SS VOLTAGE (V) 0.4 0.6 FB VOLTAGE (V) 3 VIN UVLO (V) 0.7 0.2 8609S G20 Soft-Start Current vs Temperature 2.5 SOFT START CURRENT (A) FB VOLTAGE (V) Soft-Start Tracking 0 0 50 8609S G19 1.0 0 40 8609S G25 200ns/DIV 36VIN TO 5VOUT AT 1A 8609S G26 Rev. C For more information www.analog.com LT8609S TYPICAL PERFORMANCE CHARACTERISTICS Transient Response Transient Response 500mA/DIV 500mA/DIV 100mV/DIV 100mV/DIV 8609S G27 50s/DIV 20s/DIV 50mA TO 1A TRANSIENT 12VIN TO 5VOUT COUT = 47F 0.5A TO 1.5A TRANSIENT 12VIN TO 5VOUT COUT = 47F Start-Up Dropout 6 6 6 5 5 5 5 VOUT 4 4 3 3 2 2 VIN 1 0 0 1 2 3 4 5 INPUT VOLTAGE (V) 6 7 INPUT VOLTAGE (V) 6 RLOAD = 2.5 VOUT 4 3 2 1 1 0 0 2 VIN 1 0 1 2 3 4 5 INPUT VOLTAGE (V) 60 CASE TEMPERATURE RISE (C) 30 20 10 0 0 0.25 0.50 0.75 1 1.25 1.50 1.75 LOAD CURRENT (A) 2 7 0 Case Temperature vs 3A Pulsed Load 60 40 6 8609S G29 Case Temperature vs Load Current 50 4 3 8609S G30 VIN = 12V VIN = 24V VOUT = 5V fSW = 2MHz 7 RLOAD = 25 OUTPUT VOLTAGE (V) 7 OUTPUT VOLTAGE (V) INPUT VOLTAGE (V) Start-Up Dropout 7 7 CASE TEMPERATURE RISE (C) 8609S G28 VIN = 12V VIN = 24V STANDBY LOAD = 50mA PULSED LOAD = 3A VOUT = 5V fSW = 2MHz 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100 DUTY CYCLE (%) 8609S G31 8609S G32 Rev. C For more information www.analog.com 7 LT8609S TYPICAL PERFORMANCE CHARACTERISTICS Conducted EMI Performance 80 PEAK DETECTOR 70 AMPLITUDE (dBV) 60 50 40 30 20 10 0 CLASS 5 PEAK LIMIT FIXED FREQUENCY SPREAD SPECTRUM MODE -10 -20 0 3 6 12 18 15 FREQUENCY (MHz) 9 24 21 30 27 8609S G33 DC2522A DEMO BOARD WITH EMI FILTER INSTALLED 14V INPUT TO 5V OUTPUT AT 2A, fSW = 2MHz Radiated EMI Performance (CISPR25 Radiated Emission Test with Class 5 Peak Limits) 50 AMPLITUDE (dBV/m) VERTICAL POLARIZATION 45 PEAK DETECTOR 40 35 30 25 20 15 10 5 0 CLASS 5 PEAK LIMIT FIXED FREQUENCY SPREAD SPECTRUM MODE -5 -10 0 100 200 300 500 400 600 FREQUENCY (MHz) 700 800 900 1000 50 AMPLITUDE (dBV/m) HORIZONTAL POLARIZATION 45 PEAK DETECTOR 40 35 30 25 20 15 10 5 0 CLASS 5 PEAK LIMIT FIXED FREQUENCY SPREAD SPECTRUM MODE -5 -10 0 100 200 300 500 400 600 FREQUENCY (MHz) DC2522A DEMO BOARD WITH EMI FILTER INSTALLED 14V INPUT TO 5V OUTPUT AT 2A, fSW = 2MHz 8 700 800 900 1000 8609S G34 Rev. C For more information www.analog.com LT8609S PIN FUNCTIONS RT (Pin 1): A resistor is tied between RT and ground to set the switching frequency. INTVCC (Pin 2): Internal 3.5V Regulator Bypass Pin. The internal power drivers and control circuits are powered from this voltage. INTVCC max output current is 20mA. Voltage on INTVCC will vary between 2.8V and 3.5V. Decouple this pin to power ground with at least a 1F low ESR ceramic capacitor. Do not load the INTVCC pin with external circuitry. GND (Pins 3, 4, 8, 14, 17): Exposed Pad Pin. These pads must be connected to the negative terminal of the input capacitor and soldered to the PCB in order to lower the thermal resistance. SW (Pins 5, 6): The SW pin is the output of the internal power switches. Connect this pin to the inductor and boost capacitor. This node should be kept small on the PCB for good performance. N/C (Corner Pins, Pin 7): Connect these pins to the ground plane for improved mechanical performance while temperature cycling. VIN (Pins 9, 10): The VIN pin supplies current to the LT8609S internal circuitry and to the internal topside power switch. This pin must be locally bypassed. Be sure to place the positive terminal of the input capacitor as close as possible to the VIN pins, and the negative capacitor terminal as close as possible to the GND pins. EN/UV (Pin 11): The LT8609S is shut down when this pin is low and active when this pin is high. The hysteretic threshold voltage is 1.05V going up and 1.00V going down. Tie to VIN if the shutdown feature is not used. An external resistor divider from VIN can be used to program a VIN threshold below which the LT8609S will shut down. PG (Pin 12): The PG pin is the open-drain output of an internal comparator. PG remains low until the FB pin is within 8.5% of the final regulation voltage, and there are no fault conditions. PG is valid when VIN is above 3.2V and EN/UV is high. PG will pull low when VIN is above 3.2V and EN/UV is low. PG will be high impedance when VIN is low. FB (Pin 13): The LT8609S regulates the FB pin to 0.774V. Connect the feedback resistor divider tap to this pin. TR/SS (Pin 15): Output Tracking and Soft-Start Pin. This pin allows user control of output voltage ramp rate during start-up. A TR/SS voltage below 0.774V forces the LT8609S to regulate the FB pin to equal the TR/SS pin voltage. When TR/SS is above 0.774V, the tracking function is disabled and the internal reference resumes control of the error amplifier. An internal 2A pull-up current from INTVCC on this pin allows a capacitor to program output voltage slew rate. This pin is pulled to ground with a 300 MOSFET during shutdown and fault conditions; use a series resistor if driving from a low impedance output. SYNC (Pin 16): External Clock Synchronization Input. Ground this pin for low ripple Burst Mode operation at low output loads. Tie to a clock source for synchronization to an external frequency. Leave floating for pulse-skipping mode with no spread spectrum modulation. Tie to INTVCC or tie to a voltage between 3.2V and 5.0V for pulse-skipping mode with spread spectrum modulation. When in pulse-skipping mode, the IQ will increase to several mA. Rev. C For more information www.analog.com 9 LT8609S BLOCK DIAGRAM VIN VIN CIN R3 OPT 0.2F EN/UV 1V + - SHDN 8.5% ERROR AMP + + - RPG CFF R2 CSS RT FB VC TR/SS SHDN TSD INTVCC UVLO VIN UVLO 2A 0.1F INTVCC BURST DETECT CVCC CBST OSCILLATOR 200kHz TO 2.2MHz VOUT R1 3.5V REG SLOPE COMP R4 OPT PG - + INTERNAL 0.774V REF SWITCH LOGIC AND ANTISHOOT THROUGH SHDN TSD VIN UVLO M1 L SW VOUT COUT M2 GND RT SYNC 8609S BD 10 Rev. C For more information www.analog.com LT8609S OPERATION The LT8609S is a monolithic constant frequency current mode step-down DC/DC converter. An oscillator with frequency set using a resistor on the RT pin turns on the internal top power switch at the beginning of each clock cycle. Current in the inductor then increases until the top switch current comparator trips and turns off the top power switch. The peak inductor current at which the top switch turns off is controlled by the voltage on the internal VC node. The error amplifier servos the VC node by comparing the voltage on the VFB pin with an internal 0.774V reference. When the load current increases it causes a reduction in the feedback voltage relative to the reference leading the error amplifier to raise the VC voltage until the average inductor current matches the new load current. When the top power switch turns off the synchronous power switch turns on until the next clock cycle begins or inductor current falls to zero. If overload conditions result in excess current flowing through the bottom switch, the next clock cycle will be delayed until switch current returns to a safe level. If the EN/UV pin is low, the LT8609S is shut down and draws 1A from the input. When the EN/UV pin is above 1V, the switching regulator becomes active. To optimize efficiency at light loads, the LT8609S enters Burst Mode operation during light load situations. Between bursts, all circuitry associated with controlling the output switch is shut down, reducing the input supply current to 1.7A. In a typical application, 2.5A will be consumed from the input supply when regulating with no load. The SYNC pin is tied low to use Burst Mode operation and can be floated to use pulse-skipping mode. If a clock is applied to the SYNC pin the part will synchronize to an external clock frequency and operate in pulse-skipping mode. While in pulse-skipping mode the oscillator operates continuously and positive SW transitions are aligned to the clock. During light loads, switch pulses are skipped to regulate the output and the quiescent current will be several mA. The SYNC pin may be tied high for spread spectrum modulation mode, and the LT8609S will operate similar to pulse-skipping mode but vary the clock frequency to reduce EMI. Comparators monitoring the FB pin voltage will pull the PG pin low if the output voltage varies more than 8.5% (typical) from the set point, or if a fault condition is present. The oscillator reduces the LT8609S's operating frequency when the voltage at the FB pin is low. This frequency foldback helps to control the inductor current when the output voltage is lower than the programmed value which occurs during start-up. When a clock is applied to the SYNC pin the frequency foldback is disabled. Frequency foldback is only enabled when the SYNC pin is tied to ground. Rev. C For more information www.analog.com 11 LT8609S APPLICATIONS INFORMATION Achieving Ultralow Quiescent Current To enhance efficiency at light loads, the LT8609S enters into low ripple Burst Mode operation, which keeps the output capacitor charged to the desired output voltage while minimizing the input quiescent current and minimizing output voltage ripple. In Burst Mode operation the LT8609S delivers single small pulses of current to the output capacitor followed by sleep periods where the output power is supplied by the output capacitor. While in sleep mode the LT8609S consumes 1.7A. As the output load decreases, the frequency of single current pulses decreases (see Figure1) and the percentage of time the LT8609S is in sleep mode increases, resulting in much higher light load efficiency than for typical converters. By maximizing the time between pulses, the 2500 FREQUENCY (kHz) 1500 1000 500 0 0 200 400 LOAD CURRENT (mA) 600 8609S F01a Figure 1a. SW Burst Mode Frequency vs Load 100 VOUT = 5V fSW = 700kHz SYNC = FLOAT 90 LOAD CURRENT (mA) 80 70 60 50 40 30 20 10 0 0 10 30 20 INPUT VOLTAGE (V) 40 10mV/DIV 2.00s/DIV 8609S F02 Figure2. Burst Mode Operation converter quiescent current approaches 2.5A for a typical application when there is no output load. Therefore, to optimize the quiescent current performance at light loads, the current in the feedback resistor divider must be minimized as it appears to the output as load current. While in Burst Mode operation the current limit of the top switch is approximately 600mA resulting in output voltage ripple shown in Figure2. Increasing the output capacitance will decrease the output ripple proportionally. As load ramps upward from zero the switching frequency will increase but only up to the switching frequency programmed by the resistor at the RT pin as shown in Table1. The output load at which the LT8609S reaches the programmed frequency varies based on input voltage, output voltage, and inductor choice. L = 2.2H VOUT = 3.3V VIN = 12V SYNC = 0V 2000 200mA/DIV 50 For some applications it is desirable for the LT8609S to operate in pulse-skipping mode, offering two major differences from Burst Mode operation. First is the clock stays awake at all times and all switching cycles are aligned to the clock. In this mode much of the internal circuitry is awake at all times, increasing quiescent current to several hundred A. Second is that full switching frequency is reached at lower output load than in Burst Mode operation as shown in Figure1b. To enable pulse-skipping mode the SYNC pin is floated. To achieve spread spectrum modulation with pulse-skipping mode, the SYNC pin is tied high. While a clock is applied to the SYNC pin the LT8609S will also operate in pulse-skipping mode. 8609S F01b Figure1b. Full Switching Frequency Minimum Load vs VIN in Pulse Skipping Mode 12 Rev. C For more information www.analog.com LT8609S APPLICATIONS INFORMATION FB Resistor Network Operating Frequency Selection and Trade-Offs The output voltage is programmed with a resistor divider between the output and the FB pin. Choose the resistor values according to: Selection of the operating frequency is a trade-off between efficiency, component size, and input voltage range. The advantage of high frequency operation is that smaller inductor and capacitor values may be used. The disadvantages are lower efficiency and a smaller input voltagerange. V R1=R2 OUT - 1 0.774V 1% resistors are recommended to maintain output voltage accuracy. The total resistance of the FB resistor divider should be selected to be as large as possible when good low load efficiency is desired: The resistor divider generates a small load on the output, which should be minimized to optimize the quiescent current at low loads. When using large FB resistors, a 10pF phase lead capacitor should be connected from VOUT to FB. Setting the Switching Frequency The LT8609S uses a constant frequency PWM architecture that can be programmed to switch from 200kHz to 2.2MHz by using a resistor tied from the RT pin to ground. A table showing the necessary RT value for a desired switching frequency is in Table1. When in spread spectrum modulation mode, the frequency is modulated upwards of the frequency set by RT. Table1. SW Frequency vs RT Value fSW (MHz) RT (k) 0.2 221 0.300 143 0.400 110 0.500 86.6 0.600 71.5 0.700 60.4 0.800 52.3 0.900 46.4 1.000 40.2 1.200 33.2 1.400 27.4 1.600 23.7 1.800 20.5 2.000 18.2 2.200 16.2 The highest switching frequency (fSW(MAX)) for a given application can be calculated as follows: fSW(MAX) = ( VOUT + VSW(BOT) tON(MIN) VIN - VSW(TOP) + VSW(BOT) ) where VIN is the typical input voltage, VOUT is the output voltage, VSW(TOP) and VSW(BOT) are the internal switch drops (~0.4V, ~0.25V, respectively at max load) and tON(MIN) is the minimum top switch on-time (see Electrical Characteristics). This equation shows that slower switching frequency is necessary to accommodate a high VIN/ VOUT ratio. For transient operation VIN may go as high as the Abs Max rating regardless of the RT value, however the LT8609S will reduce switching frequency as necessary to maintain control of inductor current to assure safe operation. The LT8609S is capable of maximum duty cycle approaching 100%, and the VIN to VOUT dropout is limited by the RDS(ON) of the top switch. In this mode the LT8609S skips switch cycles, resulting in a lower switching frequency than programmed by RT. For applications that cannot allow deviation from the programmed switching frequency at low VIN/VOUT ratios use the following formula to set switching frequency: VIN(MIN) = VOUT + VSW(BOT) 1- fSW * tOFF(MIN) - VSW(BOT) + VSW(TOP) where VIN(MIN) is the minimum input voltage without skipped cycles, VOUT is the output voltage, VSW(TOP) and VSW(BOT) are the internal switch drops (~0.4V, ~0.25V, respectively at max load), fSW is the switching frequency (set by RT), and tOFF(MIN) is the minimum switch offtime. Note that higher switching frequency will increase the minimum input voltage below which cycles will be dropped to achieve higher duty cycle. Rev. C For more information www.analog.com 13 LT8609S APPLICATIONS INFORMATION Inductor Selection and Maximum Output Current The LT8609S is designed to minimize solution size by allowing the inductor to be chosen based on the output load requirements of the application. During overload or short circuit conditions the LT8609S safely tolerates operation with a saturated inductor through the use of a high speed peak-current mode architecture. A good first choice for the inductor value is: L= VOUT + VSW(BOT) fSW where fSW is the switching frequency in MHz, VOUT is the output voltage, VSW(BOT) is the bottom switch drop (~0.25V) and L is the inductor value in H. To avoid overheating and poor efficiency, an inductor must be chosen with an RMS current rating that is greater than the maximum expected output load of the application. In addition, the saturation current (typically labeled ISAT) rating of the inductor must be higher than the load current plus 1/2 of in inductor ripple current: 1 IL(PEAK) =ILOAD(MAX) + L 2 where IL is the inductor ripple current as calculated several paragraphs below and ILOAD(MAX) is the maximum output load for a given application. As a quick example, an application requiring 1A output should use an inductor with an RMS rating of greater than 1A and an ISAT of greater than 1.3A. To keep the efficiency high, the series resistance (DCR) should be less than 0.04, and the core material should be intended for high frequency applications. The LT8609S limits the peak switch current in order to protect the switches and the system from overload faults. The top switch current limit (ILIM) is typically 4.75A at low duty cycles and decreases linearly to 4.0A at D = 0.8. The inductor value must then be sufficient to supply the desired maximum output current (IOUT(MAX)), which is a function of the switch current limit (ILIM) and the ripplecurrent: IOUT(MAX) =ILIM - 14 IL 2 The peak-to-peak ripple current in the inductor can be calculated as follows: IL = VOUT V 1- OUT L * fSW VIN(MAX) where fSW is the switching frequency of the LT8609S, and L is the value of the inductor. Therefore, the maximum output current that the LT8609S will deliver depends on the minimum switch current limit, the inductor value, and the input and output voltages. The inductor value may have to be increased if the inductor ripple current does not allow sufficient maximum output current (IOUT(MAX)) given the switching frequency, and maximum input voltage used in the desired application. The optimum inductor for a given application may differ from the one indicated by this design guide. A larger value inductor provides a higher maximum load current and reduces the output voltage ripple. For applications requiring smaller load currents, the value of the inductor may be lower and the LT8609S may operate with higher ripple current. This allows use of a physically smaller inductor, or one with a lower DCR resulting in higher efficiency. Be aware that low inductance may result in discontinuous mode operation, which further reduces maximum load current. The internal circuitry of the LT8609S is capable of supplying IOUT(MAX) up to 3A. Thermal limitations of the LT8609S prevent continuous output of 3A loads due to unsafe operating temperatures. In order to ensure safe operating temperature, the average LT8609S current must be kept below 2A, but will allow transient peaks up to 3A or IOUT(MAX). If high average currents cause unsafe heating of the part, the LT8609S will stop switching and indicate a fault condition to protect the internal circuitry. For more information about maximum output current and discontinuous operation, see Analog Devices Application Note 44. Finally, for duty cycles greater than 50% (VOUT/VIN > 0.5), a minimum inductance is required to avoid sub-harmonic oscillation. See Analog Devices Application Note 19. Rev. C For more information www.analog.com LT8609S APPLICATIONS INFORMATION Input Capacitor Bypass the input of the LT8609S circuit with a ceramic capacitor of X7R or X5R type. Y5V types have poor performance over temperature and applied voltage, and should not be used. A 4.7F to 10F ceramic capacitor is adequate to bypass the LT8609S and will easily handle the ripple current. Note that larger input capacitance is required when a lower switching frequency is used. If the input power source has high impedance, or there is significant inductance due to long wires or cables, additional bulk capacitance may be necessary. This can be provided with a low performance electrolytic capacitor. Step-down regulators draw current from the input supply in pulses with very fast rise and fall times. The input capacitor is required to reduce the resulting voltage ripple at the LT8609S and to force this very high frequency switching current into a tight local loop, minimizing EMI. A 4.7F capacitor is capable of this task, but only if it is placed close to the LT8609S (see the PCB Layout section). A second precaution regarding the ceramic input capacitor concerns the maximum input voltage rating of the LT8609S. A ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. If the LT8609S circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT8609S's voltage rating. This situation is easily avoided (see Analog Devices Application Note 88). Output Capacitor and Output Ripple The output capacitor has two essential functions. Along with the inductor, it filters the square wave generated by the LT8609S to produce the DC output. In this role it determines the output ripple, thus low impedance at the switching frequency is important. The second function is to store energy in order to satisfy transient loads and stabilize the LT8609S's control loop. Ceramic capacitors have very low equivalent series resistance (ESR) and provide the best ripple performance. A good starting value is: 100 COUT = VOUT * fSW where fSW is in MHz, and COUT is the recommended output capacitance in F. Use X5R or X7R types. This choice will provide low output ripple and good transient response. Transient performance can be improved with a higher value output capacitor and the addition of a feedforward capacitor placed between VOUT and FB. Increasing the output capacitance will also decrease the output voltage ripple. A lower value of output capacitor can be used to save space and cost but transient performance will suffer and may cause loop instability. See the Typical Applications in this data sheet for suggested capacitor values. When choosing a capacitor, special attention should be given to the data sheet to calculate the effective capacitance under the relevant operating conditions of voltage bias and temperature. A physically larger capacitor or one with a higher voltage rating may be required. Ceramic Capacitors Ceramic capacitors are small, robust and have very low ESR. However, ceramic capacitors can cause problems when used with the LT8609S due to their piezoelectric nature. When in Burst Mode operation, the LT8609S's switching frequency depends on the load current, and at very light loads the LT8609S can excite the ceramic capacitor at audio frequencies, generating audible noise. Since the LT8609S operates at a lower current limit during Burst Mode operation, the noise is typically very quiet to a casual ear. If this is unacceptable, use a high performance tantalum or electrolytic capacitor at the output. A final precaution regarding ceramic capacitors concerns the maximum input voltage rating of the LT8609S. As previously mentioned, a ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. If the LT8609S circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT8609S's rating. This situation is easily avoided (see Analog Devices Application Note 88). Enable Pin The LT8609S is in shutdown when the EN pin is low and active when the pin is high. The rising threshold of the EN comparator is 1.05V, with 50mV of hysteresis. The EN pin Rev. C For more information www.analog.com 15 LT8609S APPLICATIONS INFORMATION can be tied to VIN if the shutdown feature is not used, or tied to a logic level if shutdown control is required. Adding a resistor divider from VIN to EN programs the LT8609S to regulate the output only when VIN is above a desired voltage (see Block Diagram). Typically, this threshold, VIN(EN), is used in situations where the input supply is current limited, or has a relatively high source resistance. A switching regulator draws constant power from the source, so source current increases as source voltage drops. This looks like a negative resistance load to the source and can cause the source to current limit or latch low under low source voltage conditions. The VIN(EN) threshold prevents the regulator from operating at source voltages where the problems might occur. This threshold can be adjusted by setting the values R3 and R4 such that they satisfy the following equation: R3 VIN(EN) = +1 *1V R4 where the LT8609S will remain off until VIN is above VIN(EN). Due to the comparator's hysteresis, switching will not stop until the input falls slightly below VIN(EN). When in Burst Mode operation for light-load currents, the current through the VIN(EN) resistor network can easily be greater than the supply current consumed by the LT8609S. Therefore, the VIN(EN) resistors should be large to minimize their effect on efficiency at low loads. INTVCC Regulator An internal low dropout (LDO) regulator produces the 3.5V supply from VIN that powers the drivers and the internal bias circuitry. The INTVCC can supply enough current for the LT8609S's circuitry and must be bypassed to ground with a minimum of 1F ceramic capacitor. Good bypassing is necessary to supply the high transient currents required by the power MOSFET gate drivers. Applications with high input voltage and high switching frequency will increase die temperature because of the higher power dissipation across the LDO. Do not connect an external load to the INTVCC pin. 16 Output Voltage Tracking and Soft-Start The LT8609S allows the user to program its output voltage ramp rate by means of the TR/SS pin. An internal 2A pulls up the TR/SS pin to INTVCC. Putting an external capacitor on TR/SS enables soft-starting the output to prevent current surge on the input supply. During the softstart ramp the output voltage will proportionally track the TR/SS pin voltage. For output tracking applications, TR/ SS can be externally driven by another voltage source. From 0V to 0.774V, the TR/SS voltage will override the internal 0.774V reference input to the error amplifier, thus regulating the FB pin voltage to that of TR/SS pin. When TR/SS is above 0.774V, tracking is disabled and the feedback voltage will regulate to the internal reference voltage. An active pull-down circuit is connected to the TR/SS pin which will discharge the external soft-start capacitor in the case of fault conditions and restart the ramp when the faults are cleared. Fault conditions that clear the soft-start capacitor are the EN/UV pin transitioning low, VIN voltage falling too low, or thermal shutdown. Output Power Good When the LT8609S's output voltage is within the 8.5% window of the regulation point, which is a VFB voltage in the range of 0.716V to 0.849V (typical), the output voltage is considered good and the open-drain PG pin goes high impedance and is typically pulled high with an external resistor. Otherwise, the internal drain pull-down device will pull the PG pin low. To prevent glitching both the upper and lower thresholds include 0.5% of hysteresis. The PG pin is also actively pulled low during several fault conditions: EN/UV pin is below 1V, INTVCC has fallen too low, VIN is too low, or thermal shutdown. Synchronization To select low ripple Burst Mode operation, tie the SYNC pin below 0.4V (this can be ground or a logic low output). To synchronize the LT8609S oscillator to an external frequency connect a square wave (with 20% to 80% duty cycle) to the SYNC pin. The square wave amplitude should have valleys that are below 0.9V and peaks above 2.7V (up to 5V). Rev. C For more information www.analog.com LT8609S APPLICATIONS INFORMATION The LT8609S will not enter Burst Mode operation at low output loads while synchronized to an external clock, but instead will pulse skip to maintain regulation. The LT8609S may be synchronized over a 200kHz to 2.2MHz range. The RT resistor should be chosen to set the LT8609S switching frequency equal to or below the lowest synchronization input. For example, if the synchronization signal will be 500kHz and higher, the RT should be selected for 500kHz. The slope compensation is set by the RT value, while the minimum slope compensation required to avoid subharmonic oscillations is established by the inductor size, input voltage, and output voltage. Since the synchronization frequency will not change the slopes of the inductor current waveform, if the inductor is large enough to avoid subharmonic oscillations at the frequency set by RT, then the slope compensation will be sufficient for all synchronization frequencies. For some applications it is desirable for the LT8609S to operate in pulse-skipping mode, offering two major differences from Burst Mode operation. First is the clock stays awake at all times and all switching cycles are aligned to the clock. Second is that full switching frequency is reached at lower output load than in Burst Mode operation as shown in Figure1b in an earlier section. These two differences come at the expense of increased quiescent current. To enable pulse-skipping mode the SYNC pin is floated. For some applications, reduced EMI operation may be desirable, which can be achieved through spread spectrum modulation. This mode operates similar to pulse skipping mode operation, with the key difference that the switching frequency is modulated up and down by a 3 kHz triangle wave. The modulation has the frequency set by RT as the low frequency, and modulates up to approximately 20% higher than the frequency set by RT. To enable spread spectrum mode, tie SYNC to INTVCC or drive to a voltage between 3.2V and 5V. and brownout conditions. The first is the switching frequency will be folded back while the output is lower than the set point to maintain inductor current control (only if SYNC=0V).. Second, the bottom switch current is monitored such that if inductor current is beyond safe levels switching of the top switch will be delayed until such time as the inductor current falls to safe levels. This allows for tailoring the LT8609S to individual applications and limiting thermal dissipation during short circuit conditions. Frequency foldback behavior depends on the state of the SYNC pin: If the SYNC pin is low or high, or floated the switching frequency will slow while the output voltage is lower than the programmed level. If the SYNC pin is connected to a clock source, the LT8609S will stay at the programmed frequency without foldback and only slow switching if the inductor current exceeds safe levels. There is another situation to consider in systems where the output will be held high when the input to the LT8609S is absent. This may occur in battery charging applications or in battery backup systems where a battery or some other supply is diode ORed with the LT8609S's output. If the VIN pin is allowed to float and the EN pin is held high (either by a logic signal or because it is tied to VIN), then the LT8609S's internal circuitry will pull its quiescent current through its SW pin. This is acceptable if the system can tolerate several A in this state. If the EN pin is grounded the SW pin current will drop to near 0.7A. However, if the VIN pin is grounded while the output is held high, regardless of EN, parasitic body diodes inside the LT8609S can pull current from the output through the SW pin and the VIN pin. Figure3 shows a connection of the VIN and EN/UV pins that will allow the LT8609S to run only when the input voltage is present and that protects against a shorted or reversed input. The LT8609S does not operate in forced continuous mode regardless of SYNC signal. D1 VIN VIN LT8609S EN/UV GND 8609S F03 Shorted and Reversed Input Protection The LT8609S will tolerate a shorted output. Several features are used for protection during output short-circuit Figure3. Reverse VIN Protection Rev. C For more information www.analog.com 17 LT8609S APPLICATIONS INFORMATION PCB Layout side of the circuit board, and their connections should be made on that layer. Place a local, unbroken ground plane under the application circuit on the layer closest to the surface layer. The SW node should be as small as possible. Finally, keep the FB and RT nodes small so that the ground traces will shield them from the SW node. The exposed pad on the bottom of the package must be soldered to ground so that the pad is connected to ground electrically and also acts as a heat sink thermally. To keep thermal resistance low, extend the ground plane as much as possible, and add thermal vias under and near the LT8609S to additional ground planes within the circuit board and on the bottom side. For mechanical performance during temperature cycles, solder the corner N/C pins to the ground plane. For proper operation and minimum EMI, care must be taken during printed circuit board layout. Figure4 shows the recommended component placement with trace, ground plane and via locations. Note that large, switched currents flow in the LT8609S's VIN pins, GND pins, and the input capacitor (CIN). The loop formed by the input capacitor should be as small as possible by placing the capacitor adjacent to the VIN and GND pins. When using a physically large input capacitor the resulting loop may become too large in which case using a small case/value capacitor placed close to the VIN and GND pins plus a larger capacitor further away is preferred. These components, along with the inductor and output capacitor, should be placed on the same GROUND PLANE ON LAYER 2 RT R2 CSS CFF RPG R1 CVCC R4 R3 1 CIN COUT L GND VIA VIN VIA VOUT VIA OTHER SIGNAL VIA 8609S F04 Figure4. PCB Layout 18 Rev. C For more information www.analog.com LT8609S APPLICATIONS INFORMATION Thermal Considerations and Peak Current Output For higher ambient temperatures, care should be taken in the layout of the PCB to ensure good heat sinking of the LT8609S. The exposed pad on the bottom of the package must be soldered to a ground plane. This ground should be tied to large copper layers below with thermal vias; these layers will spread heat dissipated by the LT8609S. Placing additional vias can reduce thermal resistance further. The maximum load current should be derated as the ambient temperature approaches the maximum junction rating. Power dissipation within the LT8609S can be estimated by calculating the total power loss from an efficiency measurement and subtracting the inductor loss. The die temperature is calculated by multiplying the LT8609S power dissipation by the thermal resistance from junction to ambient. The LT8609S will stop switching and indicate a fault condition if safe junction temperature is exceeded. Temperature rise of the LT8609S is worst when operating at high load, high VIN, and high switching frequency. If the case temperature is too high for a given application, then either VIN, switching frequency or load current can be decreased to reduce the temperature to an acceptable level. Figure5 shows how case temperature rise can be managed by reducing VIN. The LT8609S's internal power switches are capable of safely delivering up to 3A of peak output current. However, due to thermal limits, the package can only handle 3A loads for short periods of time. This time is determined by how quickly the case temperature approaches the maximum junction rating. Figure6 shows an example of how case temperature rise changes with the duty cycle of a 10Hz pulsed 3A load. Junction temperature will be higher than case temperature. 60 VIN = 12V VIN = 24V VOUT = 5V fSW = 2MHz 50 40 CASE TEMPERATURE RISE (C) CASE TEMPERATURE RISE (C) 60 30 20 10 0 0 0.25 0.50 0.75 1 1.25 1.50 1.75 LOAD CURRENT (A) VIN = 12V VIN = 24V STANDBY LOAD = 50mA PULSED LOAD = 3A VOUT = 5V fSW = 2MHz 50 40 30 20 10 0 2 8609S F05 0 10 20 30 40 50 60 70 80 90 100 DUTY CYCLE (%) 8609S F06 Figure5. Case Temperature Rise vs Load Current Figure6. Case Temperature Rise vs 3A Pulsed Load Rev. C For more information www.analog.com 19 LT8609S TYPICAL APPLICATIONS 3.3V Step Down VIN 3.8V TO 42V VIN C2 4.7F L1 2.2H EN/UV SYNC SW R4 100k LT8609S INTVCC C3 1F PG C5 10pF TR/SS C6 10nF R1 18.2k RT GND FB fSW = 2MHz R3 309k R2 1M L1 = XFL4020-222ME VOUT 3.3V 2A POWER GOOD C4 22F X7R 1206 8609S TA02 5V Step Down VIN 5V TO 42V VIN C2 4.7F L1 2.2H EN/UV SYNC SW R4 100k LT8609S INTVCC C3 1F PG C5 10pF TR/SS C6 10nF R1 18.2k RT GND FB fSW = 2MHz R3 182k R2 1M L1 = XFL4020-222ME VOUT 5V 2A POWER GOOD C4 22F X7R 1206 8609S TA03 12V Step Down VIN 12.5V TO 42V VIN C2 4.7F L1 10H EN/UV SYNC SW R4 100k LT8609S INTVCC C3 1F R1 40.2k 20 C5 10pF TR/SS C6 10nF FSW = 1MHz PG RT GND FB R3 69.8k R2 1M L1 = XAL4040-103ME VOUT 12V 2A POWER GOOD C4 22F X7R 1206 8609S TA04 Rev. C For more information www.analog.com LT8609S TYPICAL APPLICATIONS 1.8V 2MHz Step-Down Converter VIN 3.1V TO 20V (42V TRANSIENT) C2 4.7F VIN L1 2.2H EN/UV LT8609S SW R4 100k SYNC INTVCC C3 1F PSKIP C6 10nF M1 NFET R1 18.2k PG C5 10pF TR/SS RT GND FB fSW = 2MHz R3 768k R2 1M L1 = XFL4020-222ME VOUT 1.8V 2A POWER GOOD C4 47F X7R 1210 8609S TA05 Ultralow EMI 3.3V 2A Step-Down Converter VIN 4V TO 40V L2 BEAD L3 4.7H C8 4.7F C7 4.7F VIN C9 33F C2 4.7F L1 8.2H EN/UV SYNC SW R4 100K LT8609S PG INTVCC C5 10pF TR/SS C3 1F C6 10nF FB RT R1 110k fSW = 400kHz GND R3 309k R2 1M L1 = XAL4040-822 C9 = OS-CON 63SXV33M L3 = XAL4030-472 VOUT 3.3V 2A POWER GOOD C4 47F X7R 1210 8609S TA06 Rev. C For more information www.analog.com 21 For more information www.analog.com 0.70 0.05 3.50 0.05 PACKAGE OUTLINE D PACKAGE TOP VIEW 3.50 0.05 1.45 1.45 0.375 SUGGESTED PCB LAYOUT TOP VIEW 0.7500 aaa Z 2x 0.25 0.05 5 0.2500 0.0000 0.2500 PAD "A1" CORNER 0.7500 X aaa Z 0.7500 0.2500 0.0000 0.2500 0.7500 0.375 Y E 2x Z SYMBOL A A1 L b D E D1 E1 e H1 H2 aaa bbb ccc ddd eee fff DETAIL B H2 MOLD CAP MIN 0.85 0.01 0.30 0.22 H1 DETAIL C SUBSTRATE NOM 0.94 0.02 0.40 0.25 3.00 3.00 1.45 1.45 0.50 0.24 0.70 DIMENSIONS 16b eee M Z X Y fff M Z DETAIL C A1 16x 0.10 0.10 0.10 0.10 0.15 0.08 MAX 1.03 0.03 0.50 0.28 e/2 e NOTES DETAIL A DETAIL B A L (Reference LTC DWG # 05-08-1516 Rev B) ddd Z Z 22 0.375 e b 9 12 b D1 0.375 e 5 DETAIL A 16 PACKAGE BOTTOM VIEW 8 6 0.375 13 4 1 4 SEE NOTES PIN 1 NOTCH 0.25 x 45 7 SEE NOTES TRAY PIN 1 BEVEL PACKAGE IN TRAY LOADING ORIENTATION LTXXXXX CORNER SUPPORT PAD CHAMFER IS OPTIONAL COMPONENT PIN "A1" 7 LGA 16 0317 REV B THE EXPOSED HEAT FEATURE MAY HAVE OPTIONAL CORNER RADII DETAILS OF PAD #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE PAD #1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE 5 6 METAL FEATURES UNDER THE SOLDER MASK OPENING NOT SHOWN SO AS NOT TO OBSCURE THESE TERMINALS AND HEAT FEATURES 4 3. PRIMARY DATUM -Z- IS SEATING PLANE 2. ALL DIMENSIONS ARE IN MILLIMETERS NOTES: 1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M-1994 E1 ccc M Z X Y ccc M Z X Y LQFN Package 16-Lead (3mm x 3mm x 0.94mm) LT8609S PACKAGE DESCRIPTION Rev. C // bbb Z LT8609S REVISION HISTORY REV DATE DESCRIPTION A 10/17 Clarified Oscillator Frequency RT Conditions B 04/20 10/20 3 Clarified Frequency Foldback Graph 6 Clarified Block Diagram 11 Clarified Operating Frequency Selection in Applications Information 14 Clarified PCB Layout in Figure4 18 Clarified Figure5 and 6 19 Updated JA in Pin Configuration Diagram 2 Added Note 4 3 Update Electrical Characteristics table Minimum On-Time parameter with ILOAD from 1.5A to 1.75A C PAGE NUMBER Added AEC-Q statement and #W ordering information 3 1, 2 Rev. C Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license For is granted implication or otherwise under any patent or patent rights of Analog Devices. more by information www.analog.com 23 LT8609S TYPICAL APPLICATION Tracking 3.3V and 1.8V 2MHz Converters VIN 3.8V TO 20V (42V TRANSIENT) C2 4.7F C3 1F C6 10nF R1 18.2k L1 2.2H VIN EN/UV LT8609S SYNC INTVCC R4 100k PG C5 10pF TR/SS RT GND VOUT 3.3V, 2A SW FB R3 309k R2 1M POWER GOOD C4 47F fSW = 2MHz C8 4.7F R9 10k C12 1F VIN EN/UV SYNC INTVCC L2 2.2H LT8609S SW R8 100k PG C11 10pF TR/SS R10 31.6k R5 18.2k RT GND FB R7 768k R6 1M fSW = 2MHz VOUT 1.8V 2A POWER GOOD C10 47F L1, L2 = XFL4020-222ME C2,C8 = X7R 1206 C4, C10 = X7R 1210 8609S TA07 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT8606 42V, 350mA, 92% Efficiency, 2.2MHz Synchronous Step-Down DC/DC Converter VIN=3.0V to42V, VOUT(MIN)=0.778V, IQ=3A, ISD<1A, MSOP-10E and 2mmx2mm DFN-8 Packages LT8607 42V, 750mA, 93% Efficiency, 2.2MHz Synchronous Step-Down DC/DC Converter VIN=3.0V to42V, VOUT(MIN)=0.778V, IQ=3A, ISD<1A, MSOP-10E and 2mmx2mm DFN-8 Packages LT8609/LT8609A/ 42V, 2A, 94% Efficiency, 2.2MHz Synchronous MicroPower LT8609B Step-Down DC/DC Converter with IQ = 2.5A VIN=3V to42V, VOUT(MIN)=0.8V, IQ=2.5A, ISD<1A, MSOP-10E Package LT8640S 42V, 6A, 95% Efficiency, 2.2MHz Synchronous Silent Switcher 2 Step-Down DC/DC Converter with IQ = 2.5A VIN=3.4V to42V, VOUT(MIN)=0.97V, IQ=2.5A, ISD<1A, 4mmx4mm LQFN-24 Package LT8645S 65V, 8A, 95% Efficiency, 2.2MHz Synchronous Silent Switcher 2 Step-Down DC/DC Converter with IQ = 2.5A VIN=3.4V to65V, VOUT(MIN)=0.8V, IQ=2.5A, ISD<1A, 4mmx6mm LQFN-32 Package LT8640 42V, 5A, 95% Efficiency, 2.2MHz Synchronous Silent Switcher 2 Step-Down DC/DC Converter with IQ = 2.5A VIN=3.4V to42V, VOUT(MIN)=0.97V, IQ=2.5A, ISD<1A, 3mmx4mm QFN-16 Package LT8610A/ LT8610AB 42V, 3.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with IQ = 2.5A VIN=3.4Vto42V, VOUT(MIN)=0.97V, IQ=2.5A, ISD<1A, MSOP-16E Package LT8610AC 42V, 3.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with IQ = 2.5A VIN=3Vto42V, VOUT(MIN)=0.8V, IQ=2.5A, ISD<1A, MSOP-16E Package LT8610 42V, 2.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with IQ = 2.5A VIN=3.4V to42V, VOUT(MIN)=0.97V, IQ=2.5A, ISD<1A, MSOP-16E Package LT8612 42V, 6A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with IQ = 2.5A VIN=3.4V to42V, VOUT(MIN)=0.97V, IQ=3.0A, ISD<1A, 3mmx6mm QFN-28 Package LT8602 42V, Quad Output (2.5A+1.5A+1.5A+1.5A) 95% Efficiency, 2.2MHz VIN=3V to42V, VOUT(MIN)=0.8V, IQ=25A, ISD<1A, Synchronous MicroPower Step-Down DC/DC Converter with IQ = 25A 6mmx6mm QFN-40 Package 24 Rev. C 10/20 www.analog.com For more information www.analog.com ANALOG DEVICES, INC. 2017-2020