LT8609S

LT8609S (Rev. D)

Document overview

• Manufacturer or author: Analog Devices, Inc.
• PDF pages: 24

Technical content

Rev. DFor more information www.analog.com Document Feedback TYPICAL APPLICATION FEATURES DESCRIPTION 42V, 2A/3A Peak Synchronous Step-Down Regulator with 2.5µA Quiescent Current The LT®8609S is a compact, high efficiency, high speed synchronous monolithic step-down switching regulator that consumes only 1.7µA of non-switching quiescent current. The LT8609S can deliver 2A of continuous cur- rent 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 10mV P-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 1µA. A capacitor on the TR/SS pin programs the output voltage ramp rate during start-up while the PG flag signals when V OUT is within ±8.5% of the programmed output voltage as well as fault conditions. The LT8609S is available in a small 16-lead 3mm × 3mm LQFN package.

APPLICATIONS

n Silent Switcher® 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® Operation: n <2.5µA IQ Regulating 12VIN to 3.3VOUT n Output Ripple <10mVP-P n High Efficiency 2MHz Synchronous Operation: n >93% Efficiency at 1A, 12VIN to 5VOUT n 2A Maximum Continuous Output, 3A Peak T ransient 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 T racking n Small 16-Lead 3mm × 3mm LQFN Package n AEC-Q100 Qualified for Automotive Applications n General Purpose Step Down n Low EMI Step Down All registered trademarks and trademarks are the property of their respective owners. VIN EN/UVON OFF 22µF 10pF 4.7µF VIN 5.5V TO 40V 1µF VOUT 182k 8609S TA01a 2.2µH SYNC INTVCC TR/SS RT L T8609S GND SW PG FB 18.2k 5V, 2MHz Step Down 12VIN to 5VOUT Efficiency IOUT (A) EFFICIENCY (%) 100 1.50 8609S TA01b 2.502.001.000.50 fSW = 2MHz

Rev. D For more information www.analog.com PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS FB, TR/SS . SYNC Voltage . Operating Junction Temperature Range (Note 2) L T8609SE L T8609SI Storage Temperature Range Maximum Reflow (Package Body) (Note 1) N/C RT V CC GND GND N/C N/C PG EN/UV V IN VIN N/C SW SW N/C GND SYNC TR/SS GND FB 16 15 14 13 5 6 7 8 TOP VIEW LQFN PACKAGE 16-LEAD (3mm × 3mm) LQFN JEDEC BOARD: θ JA = 50°C/W, θJC(PAD) = 14°C/W (NOTE 4) DEMOBOARD: θJA = 31°C/W EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB GND ORDER INFORMATION PART NUMBER TAPE AND REEL PART MARKING* FINISH CODE PAD FINISH PACKAGE TYPE MSL RATING TEMPERA TURE RANGE LT8609SEV#PBF LT8609SEV#TRPBF LGYN e4 Au (RoHS) LQFN (Laminate Package with QFN Footprint 3 –40°C to 125°C LT8609SIV#PBF LT8609SIV#TRPBF LGYN –40°C to 125°C AUTOMOTIVE PRODUCTS LT8609SEV#WPBF LT8609SEV#WTRPBF LGYN e4 Au (RoHS) LQFN (Laminate Package with QFN Footprint 3 –40°C to 125°C LT8609SIV#WPBF LT8609SIV#WTRPBF LGYN –40°C to 125°C 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 × 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 these models.

Rev. DFor more information www.analog.com ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. 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 0°C to 125°C junction temperature. Specifications over the –40°C to 125°C operating junction temperature range are assured by design, characterization, and correlation with statistical process controls. The LT8609SI is guaranteed over the full –40°C to 125°C operating junction temperature range. Note 3: This IC includes overtemperature protection that is intended to protect the device during overload conditions. Junction temperature will exceed 150°C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature will reduce lifetime. Note 4: θ 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. PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum Input Voltage l 2.7 3.0 3.2 V VIN Quiescent Current VEN/UV = 0V, VSYNC = 0V VEN/UV = 2V, Not Switching, VSYNC = 0V, VIN ≤ 36V l 1.7 µA µA VIN Current in Regulation VIN = 6V, VOUT = 2.7V, Output Load = 100µA VIN = 6V, VOUT = 2.7V, Output Load = 1mA l l 480 700 µA µA Feedback Reference V oltage VIN = 6V, ILOAD = 100mA VIN = 6V, ILOAD = 100mA l 0.770 0.758 0.774 0.774 0.778 0.794 V V Feedback V oltage 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 ns ns Minimum Off T ime 90 130 ns Oscillator Frequency RT = 221k, ILOAD = 0.5A RT = 60.4k, ILOAD = 0.5A RT = 18.2k, ILOAD = 0.5A l l l 155 640 1.925 200 700 2.00 245 760 2.075 kHz kHz MHz T op Power NMOS On-Resistance ILOAD = 1A 185 mΩ Top Power NMOS Current Limit l 3.4 4.75 5.7 A Bottom Power NMOS On-Resistance 115 mΩ SW Leakage Current VIN = 42V, VSW = 40V 5 µA EN/UV Pin Threshold EN/UV Rising l 0.99 1.05 1.11 V EN/UV Pin Hysteresis 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 l ±200 nA PG Pull-Down Resistance VPG = 0.1V 550 1200 Ω Sync Low Input Voltage l 0.4 0.9 V Sync High Input Voltage INTVCC = 3.5V l 2.7 3.2 V TR/SS Source Current l 1 2 3 µA TR/SS Pull-Down Resistance Fault Condition, TR/SS = 0.1V 300 900 Ω Spread Spectrum Modulation Frequency V SYNC = 3.3V 0.5 3 6 kHz

Rev. D For more information www.analog.com Efficiency (3.3V Output, 2MHz, Burst Mode Operation) Efficiency (3.3V Output, 2MHz, Burst Mode Operation) Efficiency (5V Output, 2MHz, Burst Mode Operation) Efficiency (5V Output, 2MHz, Burst Mode Operation) FB Voltage Load Regulation Line Regulation No-Load Supply Current (3.3V Output) f SW = 2MHz V IN = 12V V IN = 24V L = 2.2µH I OUT (mA) 0.001 0.01 0.1 100 10k 100 EFFICIENCY (%) 8609S G04 TEMPERATURE (°C) –50 –10 110 150 768.0 769.0 770.0 771.0 772.0 773.0 774.0 775.0 776.0 777.0 778.0 FB REGULATION VOL TAGE (mV) 8609S G05 OUTPUT CURRENT (A) 0.0 0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0 2.25 2.5 –0.50 –0.40 –0.30 –0.20 –0.10 0.00 0.10 0.20 0.30 0.40 0.50 CHANGE IN V OUT (%) 8609S G06 VIN = 12V VOUT = 3.3V INPUT VOL TAGE (V) 4.0 11.6 19.2 26.8 34.4 42.0 –0.20 –0.15 –0.10 –0.05 0.00 0.05 0.10 0.15 0.20 CHANGE IN V OUT (%) 8609S G07 ILOAD = 1A VIN (V) IIN (µA) 5.0 1.5 4.0 2.0 0.5 3.5 3.0 1.0 4.5 2.5 0.0 8609S G08 504020 10 TEMPERATURE (°C) –50 –10 110 150 1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.7 2.9 3.1 3.3 INPUT CURRENT (µA) 8609S G09 VIN = 12V VOUT = 3.3V TYPICAL PERFORMANCE CHARACTERISTICS f SW = 2MHz V IN = 12V V IN = 24V L = 2.2µH I OUT (A) 0.0 0.5 1.0 1.5 2.0 2.5 100 EFFICIENCY (%) 8609S G01 f SW = 2MHz V IN = 12V V IN = 24V L = 2.2µH I OUT (mA) 0.001 0.01 0.1 100 10k 100 EFFICIENCY (%) 8609S G02 f SW = 2MHz V IN = 12V V IN = 24V L = 2.2µH I OUT (A) 0.0 0.5 1.0 1.5 2.0 2.5 100 EFFICIENCY (%) 8609S G03 No-Load Supply Current vs Temperature (Not Switching)

Rev. DFor more information www.analog.com TYPICAL PERFORMANCE CHARACTERISTICS SWITCH CURRENT = 1A TOP SW BOT SW TEMPERATURE (°C) –50 –30 –10 110 130 150 100 150 200 250 300 350 SWITCH DROP (mV) 8609S G12 DUTY CYCLE (%) 100 3.50 3.75 4.00 4.25 4.50 4.75 5.00 5.25 5.50 TOP FET CURRENT LIMIT (A) 8609S G10 TEMPERATURE (°C) –50 –10 110 150 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5.0 I SW (A) 8609S G11 Top FET Current Limit vs Duty Cycle Top FET Current Limit vs Temperature TOP SW BOT SW SWITCH CURRENT (A) 0.5 1.5 2.5 100 200 300 400 500 600 700 800 SWITCH DROP (mV) 8609S G13 SYNC = 2V , 1.5A OUT SYNC = 0V , 1.5A OUT TEMPERATURE (°C) –50 –30 –10 110 130 150 MINIMUM ON-TIME (ns) 8609S G14 TEMPERATURE (°C) –50 –30 –10 110 130 150 100 110 120 130 140 150 MINIMUM OFF–TIME (ns) 8609S G15 VIN = 6V ILOAD = 1A Switch Drop vs Temperature Switch Drop vs Switch Current Minimum On-Time vs Temperature Minimum Off-Time vs Temperature Dropout Voltage vs Load Current Switching Frequency vs Temperature LOAD CURRENT (A) DROPOUT VOL TAGE (mV) 800 200 700 300 600 500 100 400 1.5 8609S G16 31 2.5 20.5 R T = 18.2kΩ TEMPERATURE (°C) –50 –30 –10 110 130 150 1.975 1.980 1.985 1.990 1.995 2.000 2.005 SWITHCING FREQUENCY (MHz) 8609S G17

Rev. D For more information www.analog.com TYPICAL PERFORMANCE CHARACTERISTICS Burst Frequency vs Load Current Minimum Load to Full Frequency (SYNC Float to 1.9V) Frequency Foldback Soft-Start T racking Soft-Start Current vs Temperature V IN UVLO LOAD CURRENT (mA) FREQUENCY (kHz) 2500 1000 1500 500 2000 600200 400 L = 2.2µH VOUT = 3.3V VIN = 12V SYNC = 0V 8609S G18 SS VOL TAGE (V) 0.1 0.2 0.4 0.5 0.6 0.7 0.8 1.0 1.1 1.2 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 FB VOL TAGE (V) 8609S G21 INPUT VOL TAGE (V) 8609S G19 LOAD CURRENT (mA) 100 30 5020 4010 VOUT = 5V fSW = 700kHz SYNC = FLOAT FB VOL TAGE (V) FREQUENCY (kHz) 2500 1000 1500 500 2000 10.4 0.80.2 0.6 8609S G20 VIN = 12V VOUT = 3.3V SYNC = 0V RT = 18.2k TEMPERATURE (°C) –50 –30 –10 110 130 150 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 SOFT START CURRENT (µA) 8609S G22 VSS = 0.1V TEMPERATURE (°C) –55 VIN UVLO (V) 3.5 1.5 2.5 0.5 1555 125–25 65 35 95 8609S G23 Switching Waveforms Switching Waveforms Switching Waveforms 2µs/DIV 8609S G25 IL 200mA/DIV VSW 5V/DIV 12VIN TO 5VOUT AT 25mA SYNC = 0 (Burst Mode OPERATION) 200ns/DIV 8609S G26 36VIN TO 5VOUT AT 1A IL 500mA/DIV VSW 10V/DIV 200ns/DIV IL 500mA/DIV VSW 5V/DIV 8609S G24 12VIN TO 5VOUT AT 1A

Rev. DFor more information www.analog.com TYPICAL PERFORMANCE CHARACTERISTICS T ransient Response T ransient Response Case Temperature vs 3A Pulsed Load Start-Up Dropout Start-Up Dropout Case Temperature vs Load Current V IN V OUT R LOAD = 2.5Ω INPUT VOL TAGE (V) INPUT VOL TAGE (V) OUTPUT VOL TAGE (V) 8609S G30 LOAD CURRENT (A) 0.25 0.50 0.75 1.25 1.50 1.75 CASE TEMPERATURE RISE (°C) 8609S G31 VIN = 12V VIN = 24V VOUT = 5V fSW = 2MHz DUTY CYCLE (%) 100 CASE TEMPERATURE RISE (°C) 8609S G32 VIN = 12V VIN = 24V STANDBY LOAD = 50mA PULSED LOAD = 3A V OUT = 5V fSW = 2MHz 50µs/DIV 500mA/DIV 100mV/DIV 8609S G27 50mA TO 1A TRANSIENT 12V IN TO 5VOUT COUT = 47µF 20µs/DIV 500mA/DIV 100mV/DIV 8609S G28 0.5A TO 1.5A TRANSIENT 12V IN TO 5VOUT COUT = 47µF V IN V OUT R LOAD = 25Ω INPUT VOL TAGE (V) INPUT VOL TAGE (V) OUTPUT VOL TAGE (V) 8609S G29

Rev. D For more information www.analog.com Radiated EMI Performance (CISPR25 Radiated Emission Test with Class 5 Peak Limits) FREQUENCY (MHz) AMPLITUDE (dBµV/m) –10 500 900300 700 8609S G34 1000400 800200 600100 FREQUENCY (MHz) AMPLITUDE (dBµV/m) –10 500 900300 700 1000400 800200 600100 HORIZONTAL POLARIZATION PEAK DETECTOR VERTICAL POLARIZATION PEAK DETECTOR CLASS 5 PEAK LIMIT FIXED FREQUENCY SPREAD SPECTRUM MODE CLASS 5 PEAK LIMIT FIXED FREQUENCY SPREAD SPECTRUM MODE DC2522A DEMO BOARD WITH EMI FIL TER INSTALLED 14V INPUT TO 5V OUTPUT AT 2A, f SW = 2MHz FREQUENCY (MHz) AMPLITUDE (dBµV) –10 –20 15 279 21 8609S G33 3012 246 183 PEAK DETECTOR CLASS 5 PEAK LIMIT FIXED FREQUENCY SPREAD SPECTRUM MODE DC2522A DEMO BOARD WITH EMI FIL TER INSTALLED 14V INPUT TO 5V OUTPUT AT 2A, f SW = 2MHz Conducted EMI Performance TYPICAL PERFORMANCE CHARACTERISTICS

Rev. DFor more information www.analog.com 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. INTV CC max output current is 20mA. Voltage on INTV CC will vary between 2.8V and 3.5V. Decouple this pin to power ground with at least a 1μF low ESR ceramic capacitor . Do not load the INTV CC 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 inter - nal 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 V IN 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 V IN 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 hyster - etic threshold voltage is 1.05V going up and 1.00V going down. T ie 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 T racking 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 func- tion is disabled and the internal reference resumes control of the error amplifier . An internal 2μA pull-up current from INTVCC on this pin allows a capacitor to program out - put voltage slew rate. This pin is pulled to ground with a 300Ω 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-skip- ping mode with spread spectrum modulation. When in pulse-skipping mode, the IQ will increase to several mA.

Rev. D For more information www.analog.com BLOCK DIAGRAM 8609S BD RPG RT CSS VOUT CFF ++– SLOPE COMP INTERNAL 0.774V REF OSCILLATOR 200kHz TO 2.2MHz BURST DETECT 3.5V REG CBST COUT VOUT SW L SWITCH LOGIC AND ANTI- SHOOT THROUGH ERROR AMP SHDN ±8.5% VC SHDN TSD INTV CC UVLO VIN UVLO SHDN TSD V IN UVLO EN/UV 1V + – INTVCC GND PG FB TR/SS 2µA RT SYNC VINVIN CIN 0.2µF 0.1µF CVCC OPT OPT

Rev. DFor more information www.analog.com 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 V FB pin with an inter - nal 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 over- load 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 1µA 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 1.7μA. In a typical application, 2.5μA will be consumed from the input supply when regulating with no load. The SYNC pin is tied low to use Burst Mode opera- tion 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-skip- ping 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% (typ- ical) 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 fold- back 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.

optimize the quiescent current at low loads. upwards of the frequency set by RT. Table 1. SW Frequency vs RT Value tages are lower efficiency and a smaller input voltage range. control of inductor current to assure safe operation. switching frequency than programmed by R T. dropped to achieve higher duty cycle.

Rev. D For more information www.analog.com 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 oper- ation 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, V OUT is the output voltage, V SW(BOT) is the bottom switch drop (~0.25V) and L is the inductor value in μH. 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 applica - tion. 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: IL(PEAK) =ILOAD(MAX)+ 1 2 ΔL where ∆IL is the inductor ripple current as calculated sev- eral paragraphs below and I LOAD(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 I SAT of greater than 1.3A. To keep the efficiency high, the series resistance (DCR) should be less than 0.04Ω, 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 (I LIM) 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 ripple current: IOUT(MAX) =ILIM – ΔIL The peak-to-peak ripple current in the inductor can be calculated as follows: ΔIL = VOUT L • fSW 1– VOUT VIN(MAX) where fSW is the switching frequency of the LT8609S, and L is the value of the inductor . Therefore, the maximum out- put 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 requir- ing 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 sup - plying I OUT(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. DFor more information www.analog.com APPLICATIONS INFORMATION Input Capacitor Bypass the input of the LT8609S circuit with a ceramic capacitor of X7R or X5R type. Y5V types have poor per - formance over temperature and applied voltage, and should not be used. A 4.7μF to 10μF 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 sig- nificant 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 sup - ply in pulses with very fast rise and fall times. The input capacitor is required to reduce the resulting voltage rip - ple at the LT8609S and to force this very high frequency switching current into a tight local loop, minimizing EMI. A 4.7μF capacitor is capable of this task, but only if it is placed close to the LT8609S (see the PCB Layout sec - tion). 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 LT8609 S 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 pro- vide the best ripple performance. A good starting value is: COUT = 100 VOUT • fSW where fSW is in MHz, and COUT is the recommended output capacitance in μF . Use X5R or X7R types. This choice will provide low output ripple and good transient response. T ransient performance can be improved with a higher value output capacitor and the addition of a feedforward capacitor placed between VOUT and FB. Increasing the out- put capacitance will also decrease the output voltage rip- ple. A lower value of output capacitor can be used to save space and cost but transient per formance 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 capaci - tance 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 com - bined 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. D For more information www.analog.com 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 V IN to EN programs the LT8609S to regulate the output only when V IN 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: VIN(EN)= R3 R4 +1⎛ ⎝⎜ ⎞ ⎠⎟•1V where the LT8609S will remain off until V IN 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 eas- ily 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 1μF ceramic capacitor . Good bypass- ing 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 INTV CC pin. APPLICATIONS INFORMATION Output Voltage T racking and Soft-Start The LT8609S allows the user to program its output voltage ramp rate by means of the TR/SS pin. An internal 2μA 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 soft- start 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 feed- back 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 fre- quency 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. DFor more information www.analog.com 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 R T resistor should be chosen to set the LT8609S switching frequency equal to or below the low- est synchronization input. For example, if the synchro - nization 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 R T, 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 differ- ences 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 Figure 1b 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 spec- trum 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. The LT8609S does not operate in forced continuous mode regardless of SYNC signal. Shorted and Reversed Input Protection The LT8609S will tolerate a shorted output. Several fea - tures are used for protection during output short-circuit and brownout conditions. The first is the switching fre - quency 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 mon- itored 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 lim- iting 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 V IN 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 quies - cent current through its SW pin. This is acceptable if the system can tolerate several μA in this state. If the EN pin is grounded the SW pin current will drop to near 0.7µA. 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. Figure 3 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. Figure 3. VINVIN L T8609S GND 8609S F03 EN/UV Reverse VIN Protection

the ground traces will shield them from the SW node. ground electrically and also acts as a heat sink thermally. corner N/C pins to the ground plane. Figure 4. PCB Layout

temperature approaches the maximum junction rating. a fault condition if safe junction temperature is exceeded. Figure 5. Case Temperature Rise vs Load Current Figure 6. Case Temperature Rise vs 3A Pulsed Load

Rev. D For more information www.analog.com TYPICAL APPLICATIONS 3.3V Step Down 5V Step Down 12V Step Down 4.7µF 1µF 10pF 2.2µH 18.2k 309k 100k 10nF VIN EN/UV SYNC L T8609S INTVCC TR/SS RT GND FB PG SW VIN 3.8V TO 42V POWER GOOD fSW = 2MHz L1 = XFL4020-222ME VOUT 3.3V 8609S TA02 22µF X7R 1206 4.7µF 1µF 10pF 2.2µH 18.2k 182k 100k 10nF VIN EN/UV SYNC L T8609S INTVCC TR/SS RT GND FB PG SW VIN TO 42V POWER GOOD fSW = 2MHz L1 = XFL4020-222ME VOUT 8609S TA03 22µF X7R 1206 4.7µF 1µF 22µF X7R 1206 10pF 10µH 40.2k 69.8k 100k 10nF VIN EN/UV SYNC L T8609S INTVCC TR/SS RT GND FB PG SW VIN 12.5V TO 42V POWER GOOD FSW = 1MHz L1 = XAL4040-103ME VOUT 12V 8609S TA04

Rev. DFor more information www.analog.com TYPICAL APPLICATIONS 1.8V 2MHz Step-Down Converter Ultralow EMI 3.3V 2A Step-Down Converter 4.7µF 1µF 10pF 2.2µH 18.2k 768k 100k 10nF VIN EN/UV SYNC L T8609S INTVCC TR/SS RT GND FB PG SW VIN 3.1V TO 20V (42V TRANSIENT) POWER GOOD fSW = 2MHz L1 = XFL4020-222ME VOUT 1.8V 8609S TA05 PSKIP M1 NFET 47µF X7R 1210 4.7µF 1µF 10pF 8.2µH 110k 309k 100K 10nF BEAD 4.7µH 4.7µF 4.7µF VIN EN/UV SYNC L T8609S INTVCC TR/SS RT GND FB PG SW VIN 4V TO 40V POWER GOOD fSW = 400kHz L1 = XAL4040-822 C9 = OS-CON 63SXV33M L3 = XAL4030-472 VOUT 3.3V 8609S TA06 47µF X7R 1210 33µF

Rev. D For more information www.analog.com PACKAGE DESCRIPTION 16-Lead (3mm × 3mm × 0.94mm) (Reference L TC DWG # 05-08-1516 Rev B) DETAIL B A PACKAGE TOP VIEW PAD “A1” CORNER Y X aaa Z2× 16b PACKAGE BOTTOM VIEW SEE NOTES E D b 0.375 e e b DETAIL B SUBSTRATE MOLD CAP // bbb Z Z DETAIL C SUGGESTED PCB LAYOUT TOP VIEW 0.0000 0.0000 0.7500 0.2500 0.2500 0.7500 0.7500 0.2500 0.2500 0.7500 DETAIL A SEE NOTES PIN 1 NOTCH 0.25 × 45° 13 16 8 5 aaa Z 2× M X Y Z ccc MXY Z ccc M X Y Z eee M Zfff PACKAGE OUTLINE 0.25 ±0.05 0.70 ±0.05 3.50 ±0.05 3.50 ±0.05 LGA 16 0317 REV B TRAY PIN 1 BEVEL PACKAGE IN TRAY LOADING ORIENTATION COMPONENT PIN “A1” L TXXXXX 0.375 0.375 DETAIL A ddd Z 16× SYMBOL A L b D E e aaa bbb ccc ddd eee fff MIN 0.85 0.01 0.30 0.22 NOM 0.94 0.02 0.40 0.25 3.00 3.00 1.45 1.45 0.50 0.24 0.70 MAX 1.03 0.03 0.50 0.28 0.10 0.10 0.10 0.10 0.15 0.08 NOTES DIMENSIONS Z DETAIL C NOTES: 1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M-1994 2. ALL DIMENSIONS ARE IN MILLIMETERS 3. PRIMARY DATUM -Z- IS SEATING PLANE METAL FEATURES UNDER THE SOLDER MASK OPENING NOT SHOWN SO AS NOT TO OBSCURE THESE TERMINALS AND HEAT FEATURES 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

6 THE EXPOSED HEAT FEATURE MAY HAVE OPTIONAL CORNER RADII

7 CORNER SUPPORT PAD CHAMFER IS OPTIONAL

e L e/2 1.45 1.45 0.375 0.375

Rev. DFor more information www.analog.com 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 is granted by implication or otherwise under any patent or patent rights of Analog Devices.

REVISION HISTORY

REV DATE DESCRIPTION PAGE NUMBER A 10/17 Clarified Oscillator Frequency R T Conditions Clarified Frequency Foldback Graph Clarified Block Diagram Clarified Operating Frequency Selection in Applications Information Clarified PCB Layout in Figure 4 Clarified Figure 5 and 6 B 04/20 Updated θ JA in Pin Configuration Diagram Added Note 4 Update Electrical Characteristics table Minimum On-Time parameter with I LOAD from 1.5A to 1.75A C 10/20 Added AEC-Q statement and #W ordering information 1, 2 D 02/21 Added Tape and Reel in the Order Information table 2

Rev. D For more information www.analog.com www.analog.com  ANALOG DEVICES, INC. 2017-2021 RELATED PARTS TYPICAL APPLICATION PART NUMBER DESCRIPTION COMMENTS LT8606 42V, 350mA, 92% Efficiency, 2.2MHz Synchronous Step-Down DC/DC Converter VIN = 3.0V to 42V, VOUT(MIN) = 0.778V, IQ = 3µA, ISD < 1µA, MSOP-10E and 2mm × 2mm DFN-8 Packages LT8607 42V, 750mA, 93% Efficiency, 2.2MHz Synchronous Step-Down DC/DC Converter V IN = 3.0V to 42V, VOUT(MIN) = 0.778V, IQ = 3µA, ISD < 1µA, MSOP-10E and 2mm × 2mm DFN-8 Packages LT8609/LT8609A/ LT8609B 42V, 2A, 94% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I Q = 2.5µA VIN = 3V to 42V, VOUT(MIN) = 0.8V, IQ = 2.5µA, ISD < 1µA, LT8640S 42V, 6A, 95% Efficiency, 2.2MHz Synchronous Silent Switcher 2 Step-Down DC/DC Converter with I Q = 2.5µA VIN = 3.4V to 42V, VOUT(MIN) = 0.97V, IQ = 2.5µA, ISD < 1µA, 4mm × 4mm LQFN-24 Package LT8645S 65V, 8A, 95% Efficiency, 2.2MHz Synchronous Silent Switcher 2 Step-Down DC/DC Converter with I Q = 2.5µA VIN = 3.4V to 65V, VOUT(MIN) = 0.8V, IQ = 2.5µA, ISD < 1µA, 4mm × 6mm LQFN-32 Package LT8640 42V, 5A, 95% Efficiency, 2.2MHz Synchronous Silent Switcher 2 Step-Down DC/DC Converter with I Q = 2.5µA VIN = 3.4V to 42V, VOUT(MIN) = 0.97V, IQ = 2.5µA, ISD < 1µA, 3mm × 4mm QFN-16 Package LT8610A/ LT8610AB 42V , 3.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with IQ = 2.5µA VIN = 3.4V to 42V, VOUT(MIN) = 0.97V, IQ = 2.5µA, ISD < 1µA, LT8610AC 42V, 3.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I Q = 2.5µA VIN = 3V to 42V, VOUT(MIN) = 0.8V, IQ = 2.5µA, ISD < 1µA, LT8610 42V, 2.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I Q = 2.5µA VIN = 3.4V to 42V, VOUT(MIN) = 0.97V, IQ = 2.5µA, ISD < 1µA, LT8612 42V, 6A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I Q = 2.5µA VIN = 3.4V to 42V, VOUT(MIN) = 0.97V, IQ = 3.0µA, ISD < 1µA, 3mm × 6mm QFN-28 Package Synchronous MicroPower Step-Down DC/DC Converter with I Q = 25µA VIN = 3V to 42V, VOUT(MIN)= 0.8V, IQ = 25µA, ISD < 1µA, 6mm × 6mm QFN-40 Package 4.7µF 10k R10 31.6k C10 47µF C11 10pF 2.2µH 18.2k 768k 100k C12 1µF VIN EN/UV SYNC L T8609S INTVCC TR/SS RT GND FB PG SW POWER GOOD fSW = 2MHz VOUT 1.8V 8609S TA07 4.7µF 1µF 47µF 10pF 2.2µH 18.2k 309k 100k 10nF VIN EN/UV L T8609S INTVCC TR/SS RT GND FB PG SW VIN 3.8V TO 20V (42V TRANSIENT) POWER GOOD fSW = 2MHz VOUT 3.3V , 2A SYNC L1, L2 = XFL4020-222ME C2,C8 = X7R 1206 C4, C10 = X7R 1210 T racking 3.3V and 1.8V 2MHz Converters