LT8609

LT8609/LT8609A/LT8609B (Rev. J)

Document overview

• Manufacturer or author: Analog Devices, Inc.
• PDF pages: 30

Technical content

Rev. JFor more information www.analog.com Document Feedback TYPICAL APPLICATION FEATURES DESCRIPTION 42V, 3A Synchronous Step-Down Regulator with 2.5µA Quiescent Current The LT®8609/LT8609A/LT8609B is a compact, high effi - ciency, high speed synchronous monolithic step-down switching regulator that consumes only 1.7µA of non- switching quiescent current. The LT8609/ LT8609A/ LT8609B can deliver 3A of continuous current. 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 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 UVLO or to shut down the part. 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% on the adjustable output parts or ± 7.5% on the fixed output parts of the programmed output voltage as well as fault conditions. The LT8609A has slower switch edges for lower EMI emis- sions. The LT8609B operates in pulse-skipping mode only.

APPLICATIONS

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, 5VOUT from 12VIN n 3A Maximum Continuous Output n Fast Minimum Switch-On Time: 45ns n L T8609A Available in Fixed 3.3V and 5V Output n Adjustable and Synchronizable: 200kHz to 2.2MHz n Spread Spectrum Frequency Modulation for Low EMI n Allows Use of Small Inductors n Low Dropout n Peak Current Mode Operation n Accurate 1V Enable Pin Threshold n Internal Compensation n Output Soft-Start and T racking n Small 10-Lead MSOP Package, 16-Lead MSOP Pack- age, or 10-Lead 3mm × 3mm DFN Package with Side Wettable Flanks n AEC-Q100 Qualified for Automotive Applications n GSM T ransceivers n General Purpose Step-Down n Low EMI Step-Down All registered trademarks and trademarks are the property of their respective owners. VIN BST EN/UVON OFF 0.1µF 22µF 10pF 4.7µF VIN 6V TO 40V 1µF VOUT 187k

8609 TA01a

2.2µH SYNC INTVCC TR/SS RT L T8609A GND SW PG FB 18.2k 5V, 2MHz Step-Down 12VIN to 5VOUT Efficiency L = 2.2µH f SW = 2MHz I OUT (A) 0.00 0.50 1.00 1.50 2.00 2.50 100 EFFICIENCY (%)

8609 TA01b

PULSE-SKIPPING MODE, Burst Mode OPERATION SWITCH EDGE SPEED LT8609 Both Fast LT8609A Both Medium LT8609B Pulse-Skipping Fast

Rev. J For more information www.analog.com PIN CONFIGURATION ABSOLUTE MAXIMUM RATINGS F S (Note 1) BST SW INTV CC RT SYNC EN/UV V IN PG TR/SS FB GND MSE PACKAGE 10-LEAD PLASTIC MSOP θJA = 40°C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB L T8609/L T8609A TOP VIEW BST SW INTV CC RT NC EN/UV V IN PG TR/SS FB L T8609B TOP VIEW GND MSE PACKAGE 10-LEAD PLASTIC MSOP θJA = 40°C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB BST NC SW NC INTV CC RT SYNC GND EN/UV NC V IN NC PG TR/SS FB FB L T8609A TOP VIEW GND MS PACKAGE 16-LEAD PLASTIC MSOP θJA = 40°C/W , θJC(PAD) = 10°C/W EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB L T8609/L T8609A TOP VIEW GND DDM PACKAGE 10-LEAD (3mm × 3mm) PLASTIC SIDE WETTABLE DFN θJA = 45°C/W , θJC = 10°C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB

1 EN/UV

L T8609-3.3/L T8609-5 TOP VIEW GND DDM PACKAGE 10-LEAD (3mm × 3mm) PLASTIC SIDE WETTABLE DFN θJA = 45°C/W , θJC = 10°C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB V OUT BST SW INTVCC RT SYNC ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT8609EMSE#PBF LT8609EMSE#TRPBF L TGRW 10-Lead Plastic MSOP –40°C to 125°C LT8609IMSE#PBF LT8609IMSE#TRPBF L TGRW 10-Lead Plastic MSOP –40°C to 125°C LT8609HMSE#PBF LT8609HMSE#TRPBF L TGRW 10-Lead Plastic MSOP –40°C to 150°C LT8609AEMSE#PBF LT8609AEMSE#TRPBF L TGVR 10-Lead Plastic MSOP –40°C to 125°C LT8609AIMSE#PBF LT8609AIMSE#TRPBF L TGVR 10-Lead Plastic MSOP –40°C to 125°C LT8609AJMSE#PBF LT8609AJMSE#TRPBF L TGVR 10-Lead Plastic MSOP –40°C to 150°C LT8609AHMSE#PBF LT8609AHMSE#TRPBF L TGVR 10-Lead Plastic MSOP –40°C to 150°C LT8609BEMSE#PBF LT8609BEMSE#TRPBF L TGZY 10-Lead Plastic MSOP –40°C to 125°C Operating Junction Temperature Range (Note 2) LT C to 125°C LT C to 125°C LT C to 150°C C to 150°C

Rev. JFor more information www.analog.com ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT8609BIMSE#PBF LT8609BIMSE#TRPBF L TGZY 10-Lead Plastic MSOP –40°C to 125°C LT8609AEMSE16#PBF LT8609AEMSE16#TRPBF 8609A 16-Lead Plastic MSOP –40°C to 125°C LT8609AIMSE16#PBF LT8609AIMSE16#TRPBF 8609A 16-Lead Plastic MSOP –40°C to 125°C LT8609AJMSE16#PBF LT8609AJMSE16#TRPBF 8609A 16-Lead Plastic MSOP –40°C to 150°C LT8609AHMSE16#PBF LT8609AHMSE16#TRPBF 8609A 16-Lead Plastic MSOP –40°C to 150°C LT8609AEDDM#PBF LT8609AEDDM#TRPBF LHJZ 10-Lead (3mm × 3mm) Plastic Side Wettable DFN –40°C to 125°C LT8609AJDDM#PBF LT8609AJDDM#TRPBF LHJZ 10-Lead (3mm × 3mm) Plastic Side Wettable DFN –40°C to 150°C LT8609AHDDM#PBF LT8609AHDDM#TRPBF LHJZ 10-Lead (3mm × 3mm) Plastic Side Wettable DFN –40°C to 150°C LT8609AEDDM-3.3#PBF LT8609AEDDM-3.3#TRPBF LHKB 10-Lead (3mm × 3mm) Plastic Side Wettable DFN –40°C to 125°C LT8609AJDDM-3.3#PBF LT8609AJDDM-3.3#TRPBF LHKB 10-Lead (3mm × 3mm) Plastic Side Wettable DFN –40°C to 150°C LT8609AEDDM-5#PBF LT8609AEDDM-5#TRPBF LHKC 10-Lead (3mm × 3mm) Plastic Side Wettable DFN –40°C to 125°C LT8609AJDDM-5#PBF LT8609AJDDM-5#TRPBF LHKC 10-Lead (3mm × 3mm) Plastic Side Wettable DFN –40°C to 150°C LT8609AHDDM-5#PBF LT8609AHDDM-5#TRPBF LHKC 10-Lead (3mm × 3mm) Plastic Side Wettable DFN –40°C to 150°C AUTOMOTIVE PRODUCTS** LT8609EMSE#WPBF LT8609EMSE#WTRPBF L TGRW 10-Lead Plastic MSOP –40°C to 125°C LT8609IMSE#WPBF LT8609IMSE#WTRPBF L TGRW 10-Lead Plastic MSOP –40°C to 125°C LT8609HMSE#WPBF LT8609HMSE#WTRPBF L TGRW 10-Lead Plastic MSOP –40°C to 150°C LT8609AEMSE#WPBF LT8609AEMSE#WTRPBF L TGVR 10-Lead Plastic MSOP –40°C to 125°C LT8609AIMSE#WPBF LT8609AIMSE#WTRPBF L TGVR 10-Lead Plastic MSOP –40°C to 125°C LT8609AJMSE#WPBF LT8609AJMSE#WTRPBF L TGVR 10-Lead Plastic MSOP –40°C to 150°C LT8609AHMSE#WPBF LT8609AHMSE#WTRPBF L TGVR 10-Lead Plastic MSOP –40°C to 150°C LT8609AEMSE16#WPBF LT8609AEMSE16#WTRPBF 8609A 16-Lead Plastic MSOP –40°C to 125°C LT8609AIMSE16#WPBF LT8609AIMSE16#WTRPBF 8609A 16-Lead Plastic MSOP –40°C to 125°C LT8609AJMSE16#WPBF LT8609AJMSE16#WTRPBF 8609A 16-Lead Plastic MSOP –40°C to 150°C LT8609AHMSE16#WPBF LT8609AHMSE16#WTRPBF 8609A 16-Lead Plastic MSOP –40°C to 150°C LT8609AEDDM#WPBF LT8609AEDDM#WTRPBF LHJZ 10-Lead (3mm × 3mm) Plastic Side Wettable DFN –40°C to 125°C LT8609AJDDM#WPBF LT8609AJDDM#WTRPBF LHJZ 10-Lead (3mm × 3mm) Plastic Side Wettable DFN –40°C to 150°C LT8609AHDDM#WPBF LT8609AHDDM#WTRPBF LHJZ 10-Lead (3mm × 3mm) Plastic Side Wettable DFN –40°C to 150°C LT8609AEDDM-3.3#WPBF LT8609AEDDM-3.3#WTRPBF LHKB 10-Lead (3mm × 3mm) Plastic Side Wettable DFN –40°C to 125°C LT8609AJDDM-3.3#WPBF LT8609AJDDM-3.3#WTRPBF LHKB 10-Lead (3mm × 3mm) Plastic Side Wettable DFN –40°C to 150°C LT8609AEDDM-5#WPBF LT8609AEDDM-5#WTRPBF LHKC 10-Lead (3mm × 3mm) Plastic Side Wettable DFN –40°C to 125°C LT8609AJDDM-5#WPBF LT8609AJDDM-5#WTRPBF LHKC 10-Lead (3mm × 3mm) Plastic Side Wettable DFN –40°C to 150°C LT8609AHDDM-5#WPBF LT8609AHDDM-5#WTRPBF LHKC 10-Lead (3mm × 3mm) Plastic Side Wettable DFN –40°C to 150°C Contact the factory for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container . Tape and reel specifications. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix. **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. J For more information www.analog.com PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum Input Voltage l 2.7 3.0 3.2 V VIN Quiescent Current LT8609/LT8609A: VEN/UV = 0V, VSYNC = 0V VEN/UV = 2V, Not Switching, VSYNC = 0V l 1.7 µA µA LT8609B: VEN/UV = 0V VEN/UV = 2V, Not Switching 350 µA µA V IN Current in Regulation LT8609/LT8609A: VIN = 6V, VOUT = 2.7V, Output Load = 100μA VIN = 6V, VOUT = 2.7V, Output Load = 1mA l l 480 700 μA μA LT8609A-3.3: VIN = 8V, VOUT = 3.3V ILOAD = 100μA VIN = 8V, VOUT = 3.3V ILOAD = 1mA l l 480 700 μA μA LT8609A-5: VIN = 12V, VOUT = 5V ILOAD = 100μA VIN = 12V, VOUT = 5V ILOAD = 1mA l l 480 700 μA μA Feedback Reference Voltage LT8609/LT8609A: (E-, I-, H-Grade) VIN = 6V, ILOAD = 100mA VIN = 6V, ILOAD = 100mA l 0.778 0.770 0.782 0.782 0.786 0.794 V V LT8609/LT8609A: (J-Grade) VIN = 6V, ILOAD = 100mA VIN = 6V, ILOAD = 100mA l 0.778 0.766 0.782 0.782 0.786 0.798 V V LT8609B: VIN = 6V, ILOAD = 100mA VIN = 6V, ILOAD = 100mA l 0.772 0.759 0.782 0.782 0.792 0.805 V V Output Reference Voltage LT8609A-3.3: VIN = 8V, ILOAD = 100mA VIN = 8V, ILOAD = 100mA l 3.291 3.25 3.3 3.3 3.309 3.35 V V LT8609A-5: VIN = 12V, ILOAD = 100mA VIN = 12V, ILOAD = 100mA l 4.97 4.89 5.03 5.11 V V Feedback Voltage Line Regulation LT8609/LT8609A: VIN = 4.0V to 40V l 0.004 0.02 %/V Feedback Voltage Line Regulation LT8609B: VIN = 4.0V to 40V l 0.004 0.04 %/V Output Voltage Line Regulation LT8609A-3.3: VIN = 4.0V to 40V l 0.004 0.02 %/V Output Voltage Line Regulation LT8609A-5: VIN = 6.0V to 40V l 0.004 0.02 %/V Feedback Pin Input Current LT8609/LT8609A/LT8609B: VFB = 1.0V l ±20 nA Output Pin Input Current LT8609A-3.3: VOUT = 4.0V l 620 nA Output Pin Input Current LT8609A-5: VOUT = 6.0V l 425 nA Minimum On-Time ILOAD = 1.5A, SYNC = 0V ILOAD = 1.5A, SYNC = 1.9V l l ns ns Minimum Off Time 90 130 ns ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.

Rev. JFor more information www.analog.com 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 LT8609E/LT8609AE/LT8609BE 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 LT8609I/LT8609AI/LT8609BI is guaranteed over the full –40°C to 125°C operating junction temperature range. The LT8609H/LT8609AH/LT8609AJ is guaranteed over the full –40°C to 150°C operating junction temperature range. High junction temperatures degrade operating lifetimes. Operating lifetime is derated at junction temperatures greater than 125°C. 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. ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. PARAMETER CONDITIONS MIN TYP MAX UNITS Oscillator Frequency LT8609/LT8609A: 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 LT8609B: RT = 18.2k, ILOAD = 0.5A l 1.875 2.00 2.125 MHz Top Power NMOS On-Resistance ILOAD = 1A 185 mΩ Top Power NMOS Current Limit l 3.4 4.5 5.7 A Bottom Power NMOS On-Resistance 115 mΩ SW Leakage Current VIN = 42V, VSW = 40V l 15 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 LT8609/LT8609A: VEN/UV = 2V l ±20 nA LT8609B: VEN/UV = 2V l ±30 nA PG Upper Threshold Offset from VFB LT8609/LT8609A: V FB Rising l 8.5 LT8609B: VFB Rising l 8.5 PG Upper Threshold Offset from VOUT LT8609A-3.3/LT8609A-5 V OUT Rising l 7.5 PG Lower Threshold Offset from VFB LT8609/LT8609A: V FB Falling l 8.5 LT8609B: VFB Falling l 8.5 PG Lower Threshold Offset from VOUT LT8609A-3.3/LT8609A-5 V OUT Falling l 7.5 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 LT8609/LT8609A l 0.4 0.9 V Sync High Input Voltage LT8609/LT8609A: 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 LT8609/LT8609A: VSYNC = 3.3V kHz

Rev. J For more information www.analog.com LT8609 Efficiency (5V Output, Burst Mode Operation) LT8609 Efficiency (3.3V Output, 2MHz, Burst Mode Operation) LT8609 Efficiency (3.3V Output, 2MHz, Burst Mode Operation) L = 8.2µH fSW = 700kHz I OUT (mA) 0.001 0.01 0.1 100 10k 100 EFFICIENCY (%)

8609 G04

VIN = 12V VIN = 24V I OUT (A) 0.5 1.5 2.5 100 EFFICIENCY (%)

8609 G05

VIN = 12V VIN = 24V L = 2.2µH f SW = 2MHz I OUT (mA) 0.001 0.01 0.1 100 10k 100 EFFICIENCY (%)

8609 G06

VIN = 12V VIN = 24V L = 2.2µH f SW = 2MHz TYPICAL PERFORMANCE CHARACTERISTICS LT8609 Efficiency (3.3V Output, Burst Mode Operation) LT8609 Efficiency (3.3V Output, Burst Mode Operation) LT8609 Efficiency (5V Output, Burst Mode Operation) L = 8.2µH fSW = 700kHz I OUT (A) 0.5 1.5 2.5 100 EFFICIENCY (%)

8609 G01

VIN = 12V VIN = 24V L = 8.2µH f SW = 700kHz I OUT (mA) 0.001 0.01 0.1 100 10k 100 EFFICIENCY (%)

8609 G02

VIN = 12V VIN = 24V I OUT (A) 0.5 1.5 2.5 100 EFFICIENCY (%)

8609 G03

L = 8.2µH f SW = 700kHz VIN = 12V VIN = 24V LT8609 Efficiency (5V Output, 2MHz, Burst Mode Operation) LT8609 Efficiency (5V Output, 2MHz, Burst Mode Operation) FB Voltage L = 2.2µH fSW = 2MHz I OUT (A) 0.5 1.5 2.5 100 EFFICIENCY (%)

8609 G07

VIN = 12V VIN = 24V I OUT (mA) 0.001 0.01 0.1 100 10k 100 EFFICIENCY (%)

8609 G08

VIN = 12V VIN = 24V L = 2.2µH f SW = 2MHz TEMPERATURE (°C) –50 –10 110 150 775 776 777 778 779 780 781 782 783 784 785 FB REGULATION VOL TAGE (mV)

8609 G09

Rev. JFor more information www.analog.com TYPICAL PERFORMANCE CHARACTERISTICS LT8609A-3.3 VOUT Voltage Line Regulation LT8609A-5 VOUT Voltage No-Load Supply Current Tested in Regulation Load Regulation L = 2.2µH L T8609 (V OUT = 3.3V) L T8609A-3.3 L T8609A-5 INPUT VOL TAGE (V) 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 I IN (µA)

8609 G12

OUTPUT CURRENT (A) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 –0.500 –0.400 –0.300 –0.200 –0.100 0.000 0.100 0.200 0.300 0.400 0.500 CHANGE IN V OUT (%)

8609 G10

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 (%) Line Regulation

8609 G11

ILOAD = 1A No-Load Supply Current vs Temperature (N ot Switching) Top FET Current Limit vs Duty Cycle T op FET Current Limit vs Temperature 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)

8609 G13

VIN = 12V 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) Top Fet Current Limit vs Duty Cycle

8609 G14

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)

8609 G15

TEMPERATURE (°C) –50 –10 110 150 3.270 3.275 3.280 3.285 3.290 3.295 3.300 3.305 3.310 V OUT REGULATION VOL TAGE (V)

8609 G40

TEMPERATURE (°C) –50 –10 110 150 4.96 4.97 4.98 4.99 5.00 5.01 5.02 V OUT REGULATION VOL TAGE (V)

8609 G41

Rev. J For more information www.analog.com TYPICAL PERFORMANCE CHARACTERISTICS 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 L = XFL4020–222MEC LOAD CURRENT (A) 0.5 1.5 2.5 200 400 600 800 1000 DROPOUT VOL TAGE (mV)

8609 G20

SWITCH CURRENT = 1A TOP SW BOT SW TEMPERATURE (°C) –50 –30 –10 110 130 150 100 150 200 250 300 350 SWITCH DROP (mV) Switch Drop vs Temperature

8609 G16

SWITCH CURRENT (A) 0.5 1.5 2.5 100 200 300 400 500 600 700 800 SWITCH DROP (mV) Switch Drop vs Switch Current

8609 G17

TEMPERATURE (°C) –50 –30 –10 110 130 150 100 110 120 130 140 150 MINIMUM OFF–TIME (ns) Minimum Off–Time Vs Temperature

8609 G19

VIN = 6V ILOAD = 1A 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) Switching Frequency Vs Temperature

8609 G21

SYNC = 2V , 1.5A OUT SYNC = 0V , 1.5A OUT TEMPERATURE (°C) –50 –30 –10 110 130 150 MINIMUM ON-TIME (ns) Minimum On-Time Vs Temperature

8609 G18

Rev. JFor 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 Case Temperature vs Load Current Soft-Start Current vs Temperature Case Temperature vs 3A Pulsed Load 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

8609 G22

INPUT VOL TAGE (V)

8609 G23

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

8609 G24

VIN = 12V VOUT = 3.3V RT = 18.2k TEMPERATURE (°C) –55 VIN UVLO (V) 3.5 1.5 2.5 0.5 1555 125–25 65 35 95

8609 G30

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) Soft-Start T racking

8609 G25

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) Soft Start Current Vs Temperature

8609 G26

VSS = 0.1V LOAD CURRENT (A) 0.5 1.5 2.5 CASE TEMPERATURE RISE (°C)

8609 G31

VIN = 12V VIN = 24V VOUT = 5V fSW = 2MHz STANDBY LOAD = 50mA PULSED LOAD = 3A V OUT = 5V fSW = 2MHz V IN = 12V V IN = 24V DUTY CYCLE (%) 100 CASE TEMPERATURE RISE (°C) Case Temperature vs 3A Pulsed Load

8609 G32

Rev. J For more information www.analog.com TYPICAL PERFORMANCE CHARACTERISTICS T ransient Response T ransient Response Start-Up Dropout Start-Up Dropout Switching Waveforms Switching Waveforms Switching Waveforms 10µs/DIV 200mA/DIV 5V/DIV

8609 G34

SYNC = 0 500ns/DIV 1A/DIV 10V/DIV

8609 G35

8609 G33

V IN V OUT R LOAD = 25Ω INPUT VOL TAGE (V) INPUT VOL TAGE (V) OUTPUT VOL TAGE (V) Start-Up Dropout

8609 G38

V IN V OUT R LOAD = 2.5Ω INPUT VOL TAGE (V) INPUT VOL TAGE (V) OUTPUT VOL TAGE (V) Start-Up Droupout

8609 G39

50µs/DIV 500mA/DIV 100mV/DIV

8609 G36

COUT = 47µF 20µs/DIV 500mA/DIV 100mV/DIV

8609 G37

0.5A TO 1.5A TRANSIENT 12VIN TO 5VOUT COUT = 47µF

Rev. JFor more information www.analog.com PIN FUNCTIONS BST: This pin is used to provide a drive voltage, higher than the input voltage, to the topside power switch. Place a 0.1µF boost capacitor as close as possible to the IC. Do not place a resistor in series with this pin. SW: 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. INTVCC: Internal 3.5V Regulator Bypass Pin. The inter - nal 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 1μF low ESR ceramic capacitor . Do not load the INTVCC pin with exter- nal circuitry. RT: A resistor is tied between R T and ground to set the switching frequency. SYNC: External Clock Synchronization Input. Ground this pin for low ripple Burst Mode operation at low out - put 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. In the LT8609B, the SYNC pin is replaced with a no connect; the LT8609B operates in pulse-skipping mode without spread spectrum. FB (LT8609/ LT8609A/LT8609B ONL Y): The LT8609/ LT8609A/LT8609B adjustable output parts regulate the FB pin to 0.782V. Connect the feedback resistor divider tap to this pin. VOUT (LT8609A-3.3/LT8609-5 ONL Y): The L T 8609A-3.3 regulates to VOUT pin to 3.3V. This pin connects a 5.9MΩ internal feedback divider that programs the fixed output. The LT8609A-5 regulates to VOUT pin to 5V. This pin con- nects a 8.95MΩ internal feedback divider that programs the fixed output. TR/SS: 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 0.782V forces the LT8609/LT8609A/ LT8609B to regulate the FB pin to equal the TR/SS pin voltage. In the LT8609A-3.3 and LT8609A-5 fixed output voltage options the output voltage will track the TR/SS pin voltage based on a factor set by the internal feedback resistor divider . The 3.3V output options will track to a voltage 4.2 times that of the TR/SS pin, while the 5V output options will track to a voltage 6.39 times that of the TR/SS pin. When TR/SS is above 0.782V, the tracking function is disabled and the internal reference resumes control of the error amplifier . An internal 2μA pull-up current from INTV CC on this pin allows a capacitor to program output 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. PG: The PG pin is the open-drain output of an internal comparator . On the LT8609/LT8609A/LT8609B adjust - able output parts, PG remains low until the FB pin is within ±8.5% of the final regulation voltage, and there are no fault conditions. On the LT8609A-3.3/LT8609A-5 fixed output parts, PG remains low until the V OUT pin is within ±7.5% of the final regulation voltage, and there are no fault conditions. PG is valid when V IN is above 3.2V, regardless of EN/UV pin state. VIN: The VIN pin supplies current to the LT8609/LT8609A/ LT8609B 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 capaci- tor terminal as close as possible to the GND pins. EN/UV: The LT8609/ LT8609A/LT8609B 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 pro- gram a VIN threshold below which the LT8609/LT8609A/ LT8609B will shut down. GND: Exposed Pad Pin. The exposed pad must be con - nected to the negative terminal of the input capacitor and soldered to the PCB in order to lower the thermal resistance.

Rev. J For more information www.analog.com BLOCK DIAGRAM ++– SLOPE COMP INTERNAL 0.782V REF OSCILLATOR 200kHz TO 2.2MHz BURST DETECT 3.5V REG CBST COUT VOUT 8609 BD SW L BST SWITCH LOGIC AND ANTI- SHOOT THROUGH ERROR AMP SHDN ±8.5% (±7.5% FOR FIXED OUTPUT) VC SHDN TSD INTV CC UVLO VIN UVLO L T8609A-3.3/L T8609A-5 ONL Y L T8609/L T8609A/ L T8609AB ONL Y SHDN TSD V IN UVLO EN/UV 1V + RT SYNC INTVCC GND PGVOUT RPG FB R1 CFF OPT OPT RTCSS OPT VOUT TR/SS 2µA VINVIN CIN CVCC CFFVOUT VOUT

Rev. JFor more information www.analog.com OPERATION The LT8609/LT8609A/LT8609B 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 internal 0.782V reference. The LT8609A-5 and LT8609A-3.3 Fixed output parts use the V OUT pin and an internal resistor divider to generate an internal FB node. 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 LT8609/LT8609A/LT8609B 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 LT8609/LT8609A 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 cur- rent will be several mA. The SYNC pin may be tied high for spread spectrum modulation mode, and the LT8609/ LT8609 A will operate similar to pulse-skipping mode but vary the clock frequency to reduce EMI. Comparators on the LT8609/LT8609A/LT8609B adjustable output parts 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 pres- ent. Comparators on the LT8609A-3.3/LT8609 A-5 fixed output parts monitoring the VOUT pin voltage will pull the PG pin low if the output voltage varies more than ±7.5% (typical) from the set point, or if a fault condition is present. The oscillator reduces the LT8609/LT8609A’s operating frequency when the voltage at the FB pin is low, or the voltage at the V OUT pin is low on the LT8609A-3.3 or LT8609A-5 fixed voltage options. This frequency foldback helps to control the inductor current when the output volt- age 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. The LT8609B has no SYNC pin and only operates in pulse- skipping mode.

in sleep mode the LT8609/LT8609A consumes 1.7μA. Figure 2. Burst Mode Operation

8609 F02

be minimized as it appears to the output as load current. capacitance will decrease the output ripple proportionally. grammed by the resistor at the RT pin as shown in Table 1. output voltage, and inductor choice. offers two major differences from Burst Mode operation.

optimize the quiescent current at low loads. divider resistance from the VOUT pin to ground. Table 1. SW Frequency vs RT Value the minimum top switch on-time (see Typical Applications). necessary to accommodate a high VIN/VOUT ratio.

Rev. J For more information www.analog.com APPLICATIONS INFORMATION LT8609A/LT8609B will reduce switching frequency as nec- essary to maintain control of inductor current to assure safe operation. The LT8609/LT8609A/LT8609B is capable of maximum duty cycle approaching 100%, and the V IN to V OUT dropout is limited by the R DS(ON) of the top switch. In this mode the LT8609/LT8609A /LT8609B skips switch cycles, resulting in a lower switching frequency than pro- grammed by RT. For applications that cannot allow deviation from the pro- grammed 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 V IN(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 t OFF(MIN) is the minimum switch off- time. Note that higher switching frequency will increase the minimum input voltage below which cycles will be dropped to achieve higher duty cycle. Inductor Selection and Maximum Output Current The LT8609/LT8609A/LT8609B is designed to minimize solu- tion size by allowing the inductor to be chosen based on the output load requirements of the application. During overload or short circuit conditions the LT8609/LT8609A/LT8609B 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, 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 LT8609/LT8609A/LT8609B 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 (I OUT(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 f SW is the switching frequency of the LT8609/ LT8609A/LT8609B, and L is the value of the inductor . Therefore, the maximum output current that the LT8609/ LT8609A/LT8609B will deliver depends on minimum the 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.

Rev. JFor more information www.analog.com APPLICATIONS INFORMATION 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 LT8609/LT8609A/LT8609B 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. For more information about maximum output current and discontinuous operation, see 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 Application Note 19. Input Capacitor Bypass the input of the LT8609/LT8609A/LT8609B 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 4.7μF to 10μF ceramic capacitor is adequate to bypass the LT8609/LT8609A/LT8609B 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 sup - ply in pulses with very fast rise and fall times. The input capacitor is required to reduce the resulting voltage ripple at the LT8609/LT8609A/LT8609B 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 LT8609/ LT8609A/ LT8609B (see the PCB Layout section). A second precau- tion regarding the ceramic input capacitor concerns the maximum input voltage rating of the LT8609/LT8609A/ LT8609B. A ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. If the LT8609/LT8609A/LT8609B circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT8609/ LT8609A/LT8609B’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/LT8609A/LT8609B 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 stabi- lize the LT8609/LT8609A/LT8609 B’s control loop. Ceramic capacitors have very low equivalent series resistance (ESR) and provide the best ripple performance. A good starting value is: COUT = 100 VOUT • fSW where f SW is in MHz, and C OUT 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 of adjustable output parts can be improved with a higher value output capaci- tor 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 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 prob- lems when used with the LT8609/ LT8609A/LT8609B due to their piezoelectric nature. When in Burst Mode operation, the LT8609/ LT8609A/LT8609B’ s switch - ing frequency depends on the load current, and at very

Rev. J For more information www.analog.com light loads the LT8609/ LT8609A/LT8609 B can excite the ceramic capacitor at audio frequencies, generat - ing audible noise. Since the LT8609/LT8609A/LT8609B 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 LT8609/LT8609A/ LT8609B. As previously mentioned, a ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. If the LT8609/ LT8609A/LT8609B circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT8609/LT8609A/LT8609B’ s rating. This situation is easily avoided (see Application Note 88). Enable Pin The LT8609/LT8609A/LT8609B 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 can be tied to V IN 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 LT8609/LT8609A/LT8609B to regulate the output only when VIN is above a desired voltage (see Block Diagram). Typically, this threshold, V IN(EN), is used in situations where the input supply is current limited, or has a rel - atively high source resistance. A switching regulator draws constant power from the source, so source cur - rent 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 V IN(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 APPLICATIONS INFORMATION where the LT8609/LT8609A/LT8609B will remain off until VIN is above VIN(EN). Due to the comparator’s hysteresis, switch- ing 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 LT8609/LT8609A/LT8609 B. Therefore, the VIN(EN) resis- tors should be large to minimize their effect on efficiency at low loads. INTV CC Regulator An internal low dropout (LDO) regulator produces the 3.5V supply from V IN that powers the drivers and the internal bias circuitry. The INTV CC can supply enough current for the LT8609/ LT8609A/LT8609B’ s circuitry and must be bypassed to ground with a minimum of 1μF 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 tempera - ture because of the higher power dissipation across the LDO. Do not connect an external load to the INTV CC pin. Output Voltage T racking and Soft-Start The LT8609/ LT8609A/LT8609B 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 INTV CC. Putting an external capacitor on TR/ SS enables soft-starting the output to prevent cur - rent 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 0.782V, the TR/SS voltage will override the internal 0.782V reference input to the error amplifier , thus regulating the FB pin voltage to that of TR/SS pin. In the LT8609A-3.3 and LT8609A-5 fixed output voltage options the output voltage will track the TR/SS pin voltage based on a factor set by the internal feedback resistor divider . The 3.3V output options will track to a voltage 4.2 times that of the TR/SS pin, while the 5V output options will track to a voltage 6.39 times that of the TR/SS pin. When

Rev. JFor more information www.analog.com APPLICATIONS INFORMATION TR/SS is above 0.782V, 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 LT8609/ LT8609A/LT8609B’s adjustable out - put voltage is within the ±8.5% window of the regulation point, which is a V FB 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 thresh- olds include 0.5% of hysteresis. The LT8609A-3.3 and LT8609A-5 use a ±7.5% power good window around the regulation point, which for the 3.3V output version cor - responds to a 3.0525V to 3.5475V range (typical) and for the 5V output version corresponds to a 4.625V to 5.375V range (typical). 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 out - put). To synchronize the LT8609/ LT8609A 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). The LT8609/LT8609A will not enter Burst Mode opera - tion at low output loads while synchronized to an exter - nal clock, but instead will pulse skip to maintain regu - lation. The LT8609/LT8609A may be synchronized over a 200kHz to 2.2MHz range. The R T resistor should be chosen to set the LT8609/LT8609A switching frequency equal to or below the lowest synchronization input. For example, if the synchronization signal will be 500kHz and higher , the R T should be selected for 500kHz. The slope compensation is set by the RT value, while the minimum slope compensation required to avoid subharmonic oscil- lations is established by the inductor size, input voltage, and output voltage. Since the synchronization frequency will not change the slopes of the inductor current wave - form, 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 LT8609/ LT8609A to operate in pulse-skipping mode, which is the only mode available to the LT8609B. Pulse-skipping mode offers two major differences from Burst Mode operation. First is the clock stays awake at all times and all switch - ing 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 ear- lier 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 3kHz 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 LT8609/LT8609A/LT8609B does not operate in forced continuous mode regardless of SYNC signal. Shorted and Reversed Input Protection The LT8609/ LT8609A/LT8609B will tolerate a shorted output. Several features are used for protection during output short-circuit 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 cur- rent control. Second, the bottom switch current is moni- tored such that if inductor current is beyond safe levels

8609 F03

Figure 3. Reverse VIN Protection is grounded the SW pin current will drop to near 0.7µA. board and on the bottom side. temperature approaches the maximum junction rating.

8609 F04GND VIA V IN VIA V OUT VIA EN/UV VIA OTHER SIGNAL VIA

Figure 4. PCB Layout condition if safe junction temperature is exceeded.

8609 TA03

Figure 5. Case Temperature Rise vs Load Current Figure 6. Case Temperature Rise vs 3A Pulsed Load

8609 F06

8609 TA02

Rev. JFor more information www.analog.com TYPICAL APPLICATIONS 12V Step-Down 0.1µF 4.7µF 1µF 22µF 1210 10pF 10µH 40.2k 69.8k 100k 10nF VIN EN/UV SYNC L T8609 INTVCC TR/SS RT GND FB PG SW BST VIN 13V TO 42V POWER GOOD FSW = 1MHz L1 = COILCRAFT XAL4040-103ME VOUT 12V

8609 TA04

1.8V 2MHz Step-Down Converter 3.3V 2MHz Step-Down Converter 0.1µF 4.7µF 1µF 47µF 1210 10pF 2.2µH 18.2k 768k 100k 10nF VIN EN/UV SYNC L T8609 INTVCC TR/SS RT GND FB PG SW BST VIN 2.8V TO 20V (42V TRANSIENT) POWER GOOD fSW = 2MHz L1 = COILCRAFT XFL4020-222ME VOUT 1.8V

8609 TA05

0.1µF 4.7µF 1µF 47µF 1206 2.2µH 18.2k 100k 10nF VIN EN/UV SYNC L T8609A-3.3 INTVCC TR/SS RT GND PG VOUT SW BST VIN 4.3V TO 42V POWER GOOD fSW = 2MHz L1 = COILCRAFT XFL4020-222ME VOUT 3.3V

8609 TA08

Rev. J For more information www.analog.com 5V 2MHz Step-Down Converter Ultralow EMI 5V 2A Step-Down Converter 0.1µF 4.7µF 1µF 47µF 1210 10pF 8.2µH 110k 301k 100K 10nF FB1 BEAD 4.7µH 4.7µF 4.7µF VIN EN/UV SYNC L T8609A INTVCC TR/SS RT GND FB PG SW BST VIN 6V TO 40V POWER GOOD fSW = 400kHz L1 = COILCRAFT XAL4040-822 FB1 = TDK MPZ2012S221AT000 C9 = OS-CON 63SXV33M VOUT 3.3V

8609 TA06

0.1µF 4.7µF 1µF 47µF 1206 2.2µH 18.2k 100k 10nF VIN EN/UV SYNC L T8609A-5 INTVCC TR/SS RT GND PG VOUT SW BST VIN TO 42V POWER GOOD fSW = 2MHz L1 = COILCRAFT XFL4020-222ME VOUT

8609 TA09

Rev. JFor more information www.analog.com PACKAGE DESCRIPTION MSOP (MSE) 0213 REV I 0.53 ±0.152 (.021 ±.006) SEATING PLANE 0.18 (.007) 1.10 (.043) MAX 0.17 –/uni00A00.27 (.007 – .011) TYP 0.86 (.034) REF 0.50 (.0197) BSC 1 2 3 4 5 4.90 ±0.152 (.193 ±.006) 0.497 ±0.076 (.0196 ±.003) REF8 9 10 7 6 3.00 ±0.102 (.118 ±.004) (NOTE 3) 3.00 ±0.102 (.118 ±.004) (NOTE 4) NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL NOT EXCEED 0.254mm (.010") PER SIDE. 0.254 (.010) 0° – 6° TYP DETAIL “A” DETAIL “A” GAUGE PLANE 5.10 (.201) MIN 3.20 – 3.45 (.126 – .136) 0.889 ±0.127 (.035 ±.005) RECOMMENDED SOLDER PAD LAYOUT 1.68 ±0.102 (.066 ±.004) 1.88 ±0.102 (.074 ±.004) 0.50 (.0197) BSC 0.305 ± 0.038 (.0120 ±.0015) TYP BOTTOM VIEW OF EXPOSED PAD OPTION 1.68 (.066) 1.88 (.074) 0.1016 ±0.0508 (.004 ±.002) DETAIL “B” DETAIL “B” CORNER TAIL IS PART OF THE LEADFRAME FEATURE. FOR REFERENCE ONL Y NO MEASUREMENT PURPOSE

0.05 REF

0.29 REF 10-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1664 Rev I)

Rev. J For more information www.analog.com PACKAGE DESCRIPTION MSOP (MSE16) 0213 REV F 0.53 ±0.152 (.021 ±.006) SEATING PLANE 0.18 (.007) 1.10 (.043) MAX 0.17 –/uni00A00.27 (.007 – .011) TYP 0.86 (.034) REF 0.50 (.0197) BSC 16151413121110 1 2 3 4 5 6 7 8 1 8 NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL NOT EXCEED 0.254mm (.010") PER SIDE. 0.254 (.010) 0° – 6° TYP DETAIL “A” DETAIL “A” GAUGE PLANE 5.10 (.201) MIN 3.20 – 3.45 (.126 – .136) 0.889 ±0.127 (.035 ±.005) RECOMMENDED SOLDER PAD LAYOUT 0.305 ±0.038 (.0120 ±.0015) TYP 0.50 (.0197) BSC BOTTOM VIEW OF EXPOSED PAD OPTION 2.845 ±0.102 (.112 ±.004) 2.845 ±0.102 (.112 ±.004) 4.039 ±0.102 (.159 ±.004) (NOTE 3) 1.651 ±0.102 (.065 ±.004) 1.651 ±0.102 (.065 ±.004) 0.1016 ±0.0508 (.004 ±.002) 3.00 ±0.102 (.118 ±.004) (NOTE 4) 0.280 ±0.076 (.011 ±.003) REF 4.90 ±0.152 (.193 ±.006) DETAIL “B” DETAIL “B” CORNER TAIL IS PART OF THE LEADFRAME FEATURE. FOR REFERENCE ONL Y NO MEASUREMENT PURPOSE

0.12 REF

0.35 REF 16-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1667 Rev F)

Rev. JFor more information www.analog.com PACKAGE DESCRIPTION 3.00 ±0.10 (4 SIDES) NOTE: 1. DRAWING NOT TO SCALE 2. ALL DIMENSIONS ARE IN MILLIMETERS 3. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 4. EXPOSED PAD SHALL BE SOLDER PLATED 5. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 0.40 ±0.10 BOTTOM VIEW—EXPOSED PAD DETAIL A 1.65 ±0.10 (2 SIDES) 0.75 ±0.05 R = 0.125 TYP 2.40 ±0.10 (2 SIDES) 106 PIN 1 TOP MARK (SEE NOTE 5)

0.200 REF

0.00 – 0.05 (DDM) DFN REV Ø 0518 0.25 ±0.05 2.40 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 1.65 ±0.05 (2 SIDES)2.15 ±0.05 0.50 BSC 0.70 ±0.05 3.55 ±0.05 PACKAGE OUTLINE 0.25 ±0.05

0.50 BSC

10-Lead Plastic Side Wettable DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1647 Rev Ø) PIN 1 NOTCH R = 0.20 OR 0.35 × 45° CHAMFER

0.203 REF

0.40 ± 0.10

0.10 REF

Rev. J For more information www.analog.com

REVISION HISTORY

REV DATE DESCRIPTION PAGE NUMBER A 01/16 Added the LT8609A Version to Header Added the LT8609A Version to Description Clarified Description Clarified Electrical Specifications Clarified Load Regulation, Line Regulation, No-Load Supply Current vs Temperature, Minimum On-Time vs Temperature Graphs, Frequency Foldback and Soft-Start vs Temperature Graphs Clarified Block Diagram with Optional Input Resistors Replaced Figure 1 with Table 1 in text Clarified C IN Capacitor in Text and PCB Layout Clarified Typical Application All 5, 6, 7, 8 B 06/16 Clarified Switch Drop vs Switch Current Graph axis units Clarified Switching Waveforms conditions C 10/16 Added LT8609B Option Added LT8609B Option to Absolute Maximum Ratings, Added LT8609B Package Drawing and Ordering Information Clarified Electrical Parameters and Notes for LT8609B Option Clarified Top FET Current Limit vs Temperature Graph Clarified Pin Functions to Include LT8609B Clarified Operation Section to Include LT8609B Clarified Applications Information Section to Include LT8609B Clarified Graphs in Figure 5 and 6 Clarified Typical Applications Schematics All 13 – 20 21, 22, 23, 24 D 01/17 Clarified Graphs Clarified Schematics 6, 7, 20 23, 26 E 06/17 Add H-grade to the A version Modified application circuits 2, 4 21, 22, 23 F 11/17 Clarified Oscillator Frequency R T Conditions Clarified Minimum Off Time Clarified Efficiency Graph Clarified Frequency Foldback Graph Clarified Block Diagram Clarified Maximum Duty Cycle Clarified Figure 4 G 01/18 Added MSOP-16E Package option Clarified the Pin Functions 1, 2, 24

Rev. JFor 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. REV DATE DESCRIPTION PAGE NUMBER H 02/19 Changed 2A/3A to 3A. Replaced all graphs with IOUT to 3A. Added LT8609AJMSE16 and LT8609AJMSE options. Eliminated “The internal circuitry…” paragraph. Clarified Figure 4 PCB Layout. Clarified Figure 5. Eliminated “The LT8609/LT8609A/LT8609B’s…” paragraph. Updated Typical Applications. 1, 5, 6, 7, 8 21, 22 I 01/20 Added DFN version parts and J Grades. Clarified parametric table. Added fixed output graphs. Clarified Pin Functions. Clarified Block Diagram. Clarified Operation to include fixed output options. Added text for fixed output options. Added text in Output Capacitor and Output Ripple for fixed output options. Added text in Output Voltage T racking section for fixed output options. Added text in Output Power Good section for fixed output options. Clarified Typical Applications. 1, 2, 3 4, 5 6, 7 ,8 22-25 J 08/21 Clarified Output Reference Voltage for LT8609A-3.3 and Line Regulations under Electrical Characteristics table. 4

Rev. J For more information www.analog.com  ANALOG DEVICES, INC. 2015-2021 www.analog.com RELATED PARTS TYPICAL APPLICATION PART NUMBER DESCRIPTION COMMENTS 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, LT8611 42V, 2.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I Q = 2.5µA and Input/Output Current Limit/Monitor VIN = 3.4V to 42V, VOUT(MIN) = 0.97V, IQ = 2.5µA, ISD < 1µA, 3mm × 5mm QFN-24 Package LT8616 42V, Dual 2.5A + 1.5A, 95% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I Q = 5µA VIN = 3.4V to 42V, VOUT(MIN) = 0.8V, IQ = 5µA, ISD < 1µA, TSSOP-28E, 3mm × 6mm QFN-28 Packages LT8620 65V, 2.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with I Q = 2.5µA VIN = 3.4V to 65V, VOUT(MIN) = 0.97V, IQ = 2.5µA, ISD < 1µA, MSOP-16E, 3mm × 5mm QFN-24 Packages LT8614 42V, 4A, 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, 3mm × 4mm QFN-18 Package 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 LT8640 42V, 5A/7A Peak, 96% Efficiency, 3MHz 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, 3mm × 4mm QFN-18 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 0.1µF 4.7µF 10k R10 31.6k C10 47µF 1210 C11 10pF 2.2µH 18.2k 768k 100k C12 1µF VIN EN/UV SYNC L T8609 INTVCC TR/SS RT GND FB PG SW BST POWER GOOD fSW = 2MHz VOUT 1.8V

8609 TA07

0.1µF 4.7µF 1µF 47µF 1210 10pF 2.2µH 18.2k 309k 100k 10nF VIN EN/UV L T8609 INTVCC TR/SS RT GND FB PG SW BST VIN 4.3V TO 20V (42V TRANSIENT) POWER GOOD fSW = 2MHz VOUT 3.3V , 3A SYNC T racking 3.3V and 1.8V 2MHz Converters