LT8606/LT8606B 42V, 350mA Synchronous Step-Down Regulator with 2.5A Quiescent Current FEATURES DESCRIPTION Wide Input Voltage Range: 3.0V to 42V n Ultralow Quiescent Current Burst Mode(R) Operation: n <3A I Regulating 12V to 3.3V Q IN OUT n Output Ripple <10mV P-P n High Efficiency 2MHz Synchronous Operation: n >92% Efficiency at 0.35A, 12V to 5V IN OUT n 350mA Maximum Continuous Output n Fast Minimum Switch-On Time: 35ns 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 Tracking n Small Thermally Enhanced 10-Lead MSOP Package or 8-Pin 2mm x 2mm DFN Package n AEC-Q100 Qualified for Automotive Applications The LT(R)8606 is a compact, high efficiency, high speed synchronous monolithic step-down switching regulator that consumes only 1.7A of non-switching quiescent current. The LT8606 can deliver 350mA of continuous current. Low ripple Burst Mode operation enables high efficiency down to very low output currents while keeping the output ripple below 10mVP-P. 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 LT8606. The PG pin signals when VOUT is within 8.5% of the programmed output voltage as well as fault conditions. n APPLICATIONS The MSOP package includes a SYNC pin to synchronize to an external clock, or to select Burst Mode operation or pulse-skipping with or without spread-spectrum; the TR/SS pin programs soft-start or tracking. The DFN package omits these pins and can be purchased in pulse-skipping or Burst Mode operation variety. General Purpose Step-Down Converter n Low EMI Step Down PACKAGE SYNC FUNCTIONALITY LT8606MSE MSE Programmable LT8606DFN DFN Burst Mode Operation All registered trademarks and trademarks are the property of their respective owners. LT8606BDFN DFN Pulse-Skipping Mode n TYPICAL APPLICATION 12VIN to 5VOUT Efficiency 100 5V, 2MHz Step-Down C2 1F INTVCC C3 1F C6 10nF fSW = 2MHz VIN EN/UV SYNC BST SW LT8606 C1 0.1F R4 100k PG C5 10pF TR/SS RT R1 18.2k GND FB L1 10H R3 187k R2 1M VOUT 5V 350mA POWER GOOD EFFICIENCY (%) VIN 5.5V TO 42V L = 10H 95 fSW = 2MHz 90 85 80 75 70 65 60 C4 10F X7R 0805 55 50 8606 TA01a L1 = XFL3010-103ME 0 50 100 150 200 IOUT (mA) 250 300 350 8606 TA01b Rev. D Document Feedback For more information www.analog.com 1 LT8606/LT8606B ABSOLUTE MAXIMUM RATINGS (Note 1) VIN, EN/UV, PG...........................................................42V FB, TR/SS ...................................................................4V SYNC Voltage ..............................................................6V Operating Junction Temperature Range (Note 2) LT8606E............................................. -40C to 125C LT8606I.............................................. -40C to 125C LT8606J............................................. -40C to 150C LT8606H............................................. -40C to 150C Storage Temperature Range................... -65C to 150C PIN CONFIGURATION TOP VIEW TOP VIEW BST SW INTVCC RT SYNC 1 2 3 4 5 11 GND 10 9 8 7 6 8 EN/UV BST 1 EN/UV VIN PG TR/SS FB SW 2 INTVCC 3 9 GND RT 4 MSE PACKAGE 10-LEAD PLASTIC MSOP 7 VIN 6 PG 5 FB DC PACKAGE 8-LEAD (2mm x 2mm) PLASTIC DFN JA = 40C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB JA = 102C/W EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT8606EMSE#PBF LT8606EMSE#TRPBF LTGXT 10-Lead Plastic MSOP -40C to 125C LT8606IMSE#PBF LT8606IMSE#TRPBF LTGXT 10-Lead Plastic MSOP -40C to 125C LT8606HMSE#PBF LT8606HMSE#TRPBF LTGXT 10-Lead Plastic MSOP -40C to 150C LT8606EDC#TRMPBF LT8606EDC#TRPBF LGXV 8-Lead Plastic 2mm x 2mm DFN -40C to 125C LT8606IDC#TRMPBF LT8606IDC#TRPBF LGXV 8-Lead Plastic 2mm x 2mm DFN -40C to 125C LT8606HDC#TRMPBF LT8606HDC#TRPBF LGXV 8-Lead Plastic 2mm x 2mm DFN -40C to 150C LT8606BEDC#TRMPBF LT8606BEDC#TRPBF LGXW 8-Lead Plastic 2mm x 2mm DFN -40C to 125C LT8606BIDC#TRMPBF LT8606BIDC#TRPBF LGXW 8-Lead Plastic 2mm x 2mm DFN -40C to 125C LT8606BHDC#TRMPBF LT8606BHDC#TRPBF LGXW 8-Lead Plastic 2mm x 2mm DFN -40C to 150C LT8606EMSE#WPBF LT8606EMSE#WTRPBF LTGXT 10-Lead Plastic MSOP -40C to 125C LT8606IMSE#WPBF LT8606IMSE#WTRPBF LTGXT 10-Lead Plastic MSOP -40C to 125C LT8606JMSE#WPBF LT8606JMSE#WTRPBF LTGXT 10-Lead Plastic MSOP -40C to 150C LT8606HMSE#WPBF LT8606HMSE#WTRPBF LTGXT 10-Lead Plastic MSOP -40C to 150C LT8606EDC#WTRMPBF LT8606EDC#WTRPBF LGXV 8-Lead Plastic 2mm x 2mm DFN -40C to 125C AUTOMOTIVE PRODUCTS** LT8606IDC#WTRMPBF LT8606IDC#WTRPBF LGXV 8-Lead Plastic 2mm x 2mm DFN -40C to 125C LT8606JDC#WTRMPBF LT8606JDC#WTRPBF LGXV 8-Lead Plastic 2mm x 2mm DFN -40C to 150C LT8606HDC#WTRMPBF LT8606HDC#WTRPBF LGXV 8-Lead Plastic 2mm x 2mm DFN -40C to 150C 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 thesemodels. 2 Rev. D For more information www.analog.com LT8606/LT8606B ELECTRICAL CHARACTERISTICS l denotes the specifications which apply over the full operating The temperature range, otherwise specifications are at TA = 25C. PARAMETER CONDITIONS MIN Minimum Input Voltage TYP MAX 2.5 3.0 3.2 V l VIN Quiescent Current UNITS VEN/UV = 0V VEN/UV = 2V, Not Switching, VSYNC = 0V or LT8606 DFN, VIN 36V l 1 1.7 5 12 A A VIN Current in Regulation VIN = 6V, VOUT = 2.7V, Output Load = 100A VIN = 6V, VOUT = 2.7V, Output Load = 1mA l l 56 500 90 700 A A Feedback Reference Voltage MSOP Package VIN = 6V, ILOAD = 100mA VIN = 6V, ILOAD = 100mA l 0.774 0.762 0.778 0.778 0.782 0.798 V V DFN Package VIN = 6V, ILOAD = 100mA VIN = 6V, ILOAD = 100mA l 0.771 0.753 0.778 0.778 0.785 0.803 V V Feedback Voltage Line Regulation VIN = 4.0V to 40V l 0.02 0.06 %/V Feedback Pin Input Current VFB = 1V 20 nA Minimum On-Time ILOAD = 300mA, SYNC = 0V or LT8606 DFN ILOAD = 300mA, SYNC = 1.9V or LT8606B DFN l l 35 35 65 60 ns ns Minimum Off Time ILOAD = 300mA l 93 130 ns Oscillator Frequency MSOP Package RT = 221k, ILOAD = 250mA RT = 60.4k, ILOAD = 250mA RT = 18.2k, ILOAD = 250mA l l l 155 640 1.90 200 700 2.00 245 760 2.10 kHz kHz MHz DFN Package RT = 221k, ILOAD = 250mA RT = 60.4k, ILOAD = 250mA RT = 18.2k, ILOAD = 250mA l l l 140 610 1.85 200 700 2.00 260 790 2.15 kHz kHz MHz Top Power NMOS On-Resistance ILOAD = 250mA Top Power NMOS Current Limit MSOP Package l 0.65 375 0.9 1.15 A DFN Package l 0.65 1.1 1.4 A Bottom Power NMOS On-Resistance m 240 SW Leakage Current VIN = 36V EN/UV Pin Threshold EN/UV Rising m 5 l 0.99 EN/UV Pin Hysteresis 1.05 1.11 50 EN/UV Pin Current VEN/UV = 2V PG Upper Threshold Offset from VFB VFB Rising l 5.0 PG Lower Threshold Offset from VFB VFB Falling l 5.0 PG Hysteresis VPG = 42V PG Pull-Down Resistance VPG = 0.1V Sync Low Input Voltage MSOP Only l Sync High Input Voltage INTVCC = 3.5V, MSOP Only l 20 nA 8.5 13.0 % 8.5 13.0 % TR/SS Source Current MSOP Only l TR/SS Pull-Down Resistance Fault Condition, TR/SS = 0.1V, MSOP Only Spread Spectrum Modulation Frequency VSYNC = 3.3V, MSOP Only 550 0.4 1 0.5 V mV 0.5 PG Leakage A % 200 nA 1200 0.9 V 2.7 3.2 V 2 3 A 300 900 3 6 kHz Rev. D For more information www.analog.com 3 LT8606/LT8606B ELECTRICAL CHARACTERISTICS 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 LT8606E is guaranteed to meet performance specifications from 0C to 125C junction temperature. Specifications over the -40C to 125C operating junction temperature range are assured by design, characterization, and correlation with statistical process controls. The LT8606I is guaranteed over the full -40C to 125C operating junction temperature range. The LT8606H is guaranteed over the full -40C to 150C operating junction temperature range. High junction temperatures degrade operating lifetimes. Operating lifetime is derated at junction temperatures greater than 125C. Note 3: This IC includes overtemperature protection that is intended to protect the device during overload conditions. Junction temperature will exceed 150C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature will reduce lifetime. TYPICAL PERFORMANCE CHARACTERISTICS Efficiency (5V Output, Burst Mode Operation) 100 90 80 EFFICIENCY (%) 80 75 70 65 VIN = 12V VIN = 24V 55 70 60 50 40 30 0 50 100 150 200 IOUT (mA) 250 300 0 0.001 350 50 40 30 20 VIN = 12V VIN = 24V 10 4 1 IOUT (mA) 70 65 0.1 1 IOUT (mA) 10 VIN = 12V VIN = 24V 50 100 500 0 50 8606 G02 100 150 200 IOUT (mA) 250 300 350 8606 G03 Load Regulation 0.20 0.15 60 0.1 75 FB Voltage 70 0.01 80 55 780 L = 6.8H fSW = 2MHz SYNC = 0V OR LT8606 DFN 0 0.001 0.01 8606 G01 FB REGULATION VOLTAGE (mV) EFFICIENCY (%) 80 85 60 VIN = 12V VIN = 24V 10 Efficiency (3.3V Output, Burst Mode Operation) 90 90 20 60 L = 6.8H fSW = 2MHz SYNC = 0V OR LT8606 DFN 95 10 100 500 779 CHANGE IN VOUT (%) EFFICIENCY (%) 85 100 L = 10H fSW = 2MHz SYNC = 0V OR LT8606 DFN EFFICIENCY (%) L = 10H 95 fSW = 2MHz SYNC = 0V OR LT8606 DFN 90 100 Efficiency (3.3V Output, Burst Mode Operation) Efficiency (5V Output, Burst Mode Operation) 100 50 TA = 25C, unless otherwise noted. 778 777 776 0.10 0.05 0.00 -0.05 -0.10 -0.15 775 -50 -10 30 70 110 TEMPERATURE (C) 150 8606 G05 8606 G04 -0.20 0 50 100 150 200 250 OUTPUT CURRENT (mA) 300 350 8606 G06 Rev. D For more information www.analog.com LT8606/LT8606B TYPICAL PERFORMANCE CHARACTERISTICS No-Load Supply Current vs Temperature (Not Switching) No-Load Supply Current (3.3V Output Switching) Line Regulation 0.20 4.50 0.15 4.25 IIN (A) 0.05 0.00 -0.05 3.3 L = 10H SYNC = 0V OR LT8606 DFN 3.1 4.00 2.9 3.75 2.7 INPUT CURRENT (A) 0.10 3.50 3.25 3.00 2.75 -0.10 2.3 2.1 1.9 1.7 -0.15 2.25 1.5 -0.20 2.00 18 26 INPUT VOLTAGE (V) 34 42 2 10 18 26 INPUT VOLTAGE (V) 34 8606 G07 Top FET Current Limit vs Duty Cycle 1.10 TOP FET CURRENT LIMIT (A) 1.00 0.90 0.80 0.70 0 20 40 60 DUTY CYCLE (%) 1.3 -50 30 70 110 TEMPERATURE (C) 150 8606 G09 80 DUTY CYCLE = 0 1.05 1.00 0.95 0.90 -50 100 -10 30 70 110 TEMPERATURE (C) 8606 G10 150 8606 G11 Switch Drop vs Temperature 250 -10 Top FET Current Limit vs Temperature 1.10 0.60 42 8606 G08 Switch Drop vs Switch Current 200 SWITCH CURRENT = 350mA 175 200 SWITCH DROP (mV) 10 TOP FET CURRENT LIMIT (A) 2 SYNC = 0V OR LT8606 DFN 2.5 2.50 SWITCH DROP (mV) CHANGE IN VOUT (%) TA = 25C, unless otherwise noted. 150 100 50 TOP SW BOT SW 0 -50 -30 -10 10 30 50 70 90 110 130 150 TEMPERATURE (C) 150 125 100 75 50 TOP SW BOT SW 25 0 0 50 8606 G12 100 150 200 250 SWITCH CURRENT (mA) 300 350 8606 G13 Rev. D For more information www.analog.com 5 LT8606/LT8606B TYPICAL PERFORMANCE CHARACTERISTICS Minimum On-Time vs Temperature 40 Minimum Off-Time vs Temperature 110 IOUT = 350mA 39 IOUT = 300mA 105 MINIMUM OFF-TIME (ns) 38 MINIMUM ON-TIME (ns) TA = 25C, unless otherwise noted. 37 36 35 34 33 32 100 95 90 85 31 30 -50 -30 -10 10 30 50 70 90 110 130 150 TEMPERATURE (C) 80 -50 -30 -10 10 30 50 70 90 110 130 150 TEMPERATURE (C) 8606 G14 8606 G15 Switching Frequency vs Temperature Dropout Voltage vs Output Current 2025 L = XFL3010-682ME RT = 18.2k 2020 200 SWITCHING FREQUENCY (kHz) DROPOUT VOLTAGE (mV) 250 150 100 50 2015 2010 2005 2000 1995 1990 1985 1980 0 0 0.05 0.10 0.15 0.20 0.25 0.30 0.35 OUTPUT CURRENT (A) 1975 -50 -10 30 70 110 TEMPERATURE (C) 8606 G16 8606 G17 Minimum Load to Full Frequency (SYNC Float to 1.9V) (MSOP Package) Burst Frequency vs Output Current 2500 2000 OUTPUT CURRENT (mA) 2250 SWITCHING FREQUENCY (kHz) 20 L = 6.8H VIN = 12V VOUT = 3.3V SYNC = 0V OR LT8606 DFN 1750 1500 1250 1000 750 500 150 L = 10H VIN = 12V VOUT = 5V RT = 18.2k 15 10 5 250 0 0 25 50 75 100 OUTPUT CURRENT (mA) 125 0 0 5 8606 G18 6 10 15 20 25 30 35 INPUT VOLTAGE (V) 40 45 8606 G19 Rev. D For more information www.analog.com LT8606/LT8606B TYPICAL PERFORMANCE CHARACTERISTICS Soft-Start Tracking (MSOP Package) Frequency Foldback 2500 0.9 2000 0.8 1750 0.7 FB VOLTAGE (V) FREQUENCY (kHz) 1.0 SYNC = 0V OR LT8606 DFN RT = 18.2k 2250 TA = 25C, unless otherwise noted. 1500 1250 1000 750 0.6 0.5 0.4 0.3 500 0.2 250 0.1 0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 FB VOLTAGE (V) 0 0 0.1 0.2 0.4 0.5 0.6 0.7 0.8 1.0 1.1 1.2 SS VOLTAGE (V) 8606 G20 8606 G21 Soft-Start Current vs Temperature (MSOP Package) 2.5 3.25 VIN UVLO 2.3 3.00 2.2 VIN UVLO (V) SOFT START CURRENT (A) 2.4 2.1 2.0 1.9 2.75 2.50 1.8 1.7 2.25 1.6 1.5 -50 -30 -10 10 30 50 70 90 110 130 150 TEMPERATURE (C) 2.00 -50 -30 -10 10 30 50 70 90 110 130 150 TEMPERATURE (C) 8606 G22 8606 G23 Start-Up Dropout 6 6 6 5 5 5 5 4 4 4 4 3 3 3 3 2 2 2 2 1 0 VIN VOUT 0 1 2 3 4 5 INPUT VOLTAGE (V) 6 7 INPUT VOLTAGE (V) 6 RLOAD = 50 1 1 0 0 7 RLOAD = 15 1 VIN VOUT 0 1 8606 G24 2 3 4 5 INPUT VOLTAGE (V) 6 OUTPUT VOLTAGE (V) 7 OUTPUT VOLTAGE (V) INPUT VOLTAGE (V) Start-Up Dropout 7 7 7 0 8606 G25 Rev. D For more information www.analog.com 7 LT8606/LT8606B TYPICAL PERFORMANCE CHARACTERISTICS Switching Waveforms TA = 25C, unless otherwise noted. Switching Waveforms Switching Waveforms SW 5V/DIV VSW 10V/DIV VSW 5V/DIV VOUT 20mV/DIV ILOAD 100mA/DIV ILOAD 100mA/DIV ILOAD 100mA/DIV 8606 G26 200ns/DIV 12VIN TO 5VOUT AT 250mA 2MHz 8606 G27 200ns/DIV 36VIN TO 5VOUT AT 250mA 2MHz Transient Response 2s/DIV 12VIN TO 5VOUT AT 5mA 10F COUT 8606 G28 Transient Response VOUT 100mV/DIV VOUT 100mV/DIV ILOAD 100mA/DIV ILOAD 100mA/DIV 8606 G29 200s/DIV VIN =12V, VOUT = 5V 25mA TO 275mA COUT = 22F fSW = 2MHz 8606 G30 200s/DIV VIN =12V, VOUT = 5V 100mA TO 350mA COUT = 22F fSW = 2MHz Radiated EMI Performance (CISPR25 Radiated Emission Test with Class 5 Peak Limits) 50 VERTICAL POLARIZATION 45 PEAK DETECTOR 40 AMPLITUDE (dBV) 35 30 25 20 15 10 5 0 CLASS 5 PEAK LIMIT SPREAD SPECTRUM MODE FIXED FREQUENCY -5 -10 0 100 200 300 400 500 600 700 800 900 1000 FREQUENCY (MHz) DC2564A DEMO BOARD WITH EMI FILTER INSTALLED 14V INPUT TO 5V OUTPUT AT 350mA, fSW = 2MHz 8 8606 G31 Rev. D For more information www.analog.com LT8606/LT8606B PIN FUNCTIONS BST: This pin is used to provide a drive voltage, higher than the input voltage, to the topside power switch. Place a 0.1F 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 internal power drivers and control circuits are powered from this voltage. INTVCC max output current is 20mA. Voltage on INTVCC will vary between 2.8V and 3.5V. Decouple this pin to power ground with at least a 1F low ESR ceramic capacitor. Do not load the INTVCC pin with external circuitry. RT: A resistor is tied between RT and ground to set the switching frequency. When synchronizing, the RT resistor should be chosen to set the LT8606 switching frequency to equal or below the lowest synchronization input. SYNC (MSOP Only): External Clock Synchronization Input. Ground this pin for low ripple Burst Mode operation at low output loads. Tie to a clock source for synchronization to an external frequency. Leave floating for pulse-skipping mode with no spread spectrum modulation. Tie to INTVCC or tie to a voltage between 3.2V and 5.0V for pulse-skipping mode with spread spectrum modulation. When in pulse-skipping mode, the IQ regulating no load will increase to several mA. There is no SYNC pin on the LT8606 DFN package. The LT8606 DFN package internally ties SYNC to ground. The LT8606B package internally floats SYNC. FB: The LT8606 regulates the FB pin to 0.778V. Connect the feedback resistor divider tap to this pin. TR/SS (MSOP Only): Output Tracking and Soft-Start Pin. This pin allows user control of output voltage ramp rate during start-up. A TR/SS voltage below 0.778V forces the LT8606 to regulate the FB pin to equal the TR/SS pin voltage. When TR/SS is above 0.778V, the tracking function is disabled and the internal reference resumes control of the error amplifier. An internal 2A pull-up current from INTVCC on this pin allows a capacitor to program output voltage slew rate. This pin is pulled to ground with a 300 MOSFET during shutdown and fault conditions; use a series resistor if driving from a low impedance output. There is no TR/SS pin on the LT8606 or LT8606B DFN and the node is internally floated. PG: 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 when EN/UV is high. PG is pulled low when VIN is above 3.2V and EN/UV is low. If VIN is near zero, PG will be high impedance. VIN: The VIN pin supplies current to the LT8606 internal circuitry and to the internal topside power switch. This pin must be locally bypassed. Be sure to place the positive terminal of the input capacitor as close as possible to the VIN pins, and the negative capacitor terminal as close as possible to the GND pins. EN/UV: The LT8606 is shut down when this pin is low and active when this pin is high. The hysteretic threshold voltage is 1.05V going up and 1.00V going down. Tie to VIN if the shutdown feature is not used. An external resistor divider from VIN can be used to program a VIN threshold below which the LT8606 will shut down. GND: Exposed Pad Pin. The exposed pad must be connected to the negative terminal of the input capacitor and soldered to the PCB in order to lower the thermal resistance. Rev. D For more information www.analog.com 9 LT8606/LT8606B BLOCK DIAGRAM VIN VIN CIN R3 OPT - + INTERNAL 0.778V REF EN/UV 1V + - SHDN SLOPE COMP R4 OPT PG ERROR AMP 8.5% 3.5V REG + + - INTVCC CVCC OSCILLATOR 200kHz TO 2.2MHz VC BST BURST DETECT RPG VOUT R2 CSS RT CFF R1 FB SHDN TSD INTVCC UVLO VIN UVLO TR/SS (MSOP ONLY) 2A SHDN TSD VIN UVLO SWITCH LOGIC AND ANTISHOOT THROUGH CBST M1 L SW VOUT COUT M2 GND RT SYNC (MSOP ONLY) 8606 BD 10 Rev. D For more information www.analog.com LT8606/LT8606B OPERATION The LT8606 is a monolithic constant frequency current mode step-down DC/DC converter. An oscillator with frequency set using a resistor on the RT pin turns on the internal top power switch at the beginning of each clock cycle. Current in the inductor then increases until the top switch current comparator trips and turns off the top power switch. The peak inductor current at which the top switch turns off is controlled by the voltage on the internal VC node. The error amplifier servos the VC node by comparing the voltage on the VFB pin with an internal 0.778V reference. When the load current increases it causes a reduction in the feedback voltage relative to the reference leading the error amplifier to raise the VC voltage until the average inductor current matches the new load current. When the top power switch turns off the synchronous power switch turns on until the next clock cycle begins or inductor current falls to zero. If overload conditions result in excess current flowing through the bottom switch, the next clock cycle will be delayed until switch current returns to a safe level. If the EN/UV pin is low, the LT8606 is shut down and draws 1A from the input. When the EN/UV pin is above 1.05V, the switching regulator becomes active. To optimize efficiency at light loads, the LT8606 enters Burst Mode operation during light load situations. Between bursts, all circuitry associated with controlling the output switch is shut down, reducing the input supply current to 1.7A. In a typical application, 3.0A will be consumed from the input supply when regulating with no load. The SYNC pin is tied low to use Burst Mode operation and can be floated to use pulse-skipping mode. If a clock is applied to the SYNC pin the part will synchronize to an external clock frequency and operate in pulse-skipping mode. While in pulse-skipping mode the oscillator operates continuously and positive SW transitions are aligned to the clock. During light loads, switch pulses are skipped to regulate the output and the quiescent current will be several mA. The SYNC pin may be tied high for spread spectrum modulation mode, and the LT8606 will operate similar to pulse-skipping mode but vary the clock frequency to reduce EMI. The LT8606 DFN has no SYNC pin and will always operate in Burst Mode operation. The LT8606B has no SYNC pin and will operate in pulse-skipping mode. Comparators monitoring the FB pin voltage will pull the PG pin low if the output voltage varies more than 8.5% (typical) from the set point, or if a fault condition is present. The oscillator reduces the LT8606's operating frequency when the voltage at the FB pin is low and the part is in Burst Mode operation. This frequency foldback helps to control the inductor current when the output voltage is lower than the programmed value which occurs during start-up. Rev. D For more information www.analog.com 11 LT8606/LT8606B APPLICATIONS INFORMATION 2500 Achieving Ultralow Quiescent Current As the output load decreases, the frequency of single current pulses decreases (see Figure1) and the percentage of time the LT8606 is in sleep mode increases, resulting in much higher light load efficiency than for typical converters. By maximizing the time between pulses, the converter quiescent current approaches 3.0A for a typical application when there is no output load. Therefore, to optimize the quiescent current performance at light loads, the current in the feedback resistor divider must be minimized as it appears to the output as load current. While in Burst Mode operation the current limit of the top switch is approximately 150mA resulting in output voltage ripple shown in Figure3. Increasing the output capacitance will decrease the output ripple proportionally. As load ramps upward from zero the switching frequency will increase but only up to the switching frequency programmed by the resistor at the RT pin as shown in Table1. The output load at which the LT8606 reaches the programmed frequency varies based on input voltage, output voltage, and inductor choice. For some applications it is desirable for the LT8606 to operate in pulse-skipping mode, offering two major differences from Burst Mode operation. First is the clock stays awake at all times and all switching cycles are aligned to the clock. In this mode much of the internal circuitry is awake at all times, increasing quiescent current to several hundred A. Second is that full switching frequency is reached at lower output load than in Burst Mode operation as shown in Figure2. Full Switching Frequency Minimum Load vs VIN in Pulse Skipping Mode (MSOP ONLY). To enable pulse-skipping mode the SYNC pin is floated. To achieve spread spectrum modulation with pulse-skipping mode, the SYNC pin is tied high. SWITCHING FREQUENCY (kHz) 2000 1750 1500 1250 1000 750 500 250 0 0 25 50 75 100 OUTPUT CURRENT (mA) 125 8606 F01 Figure1. SW Burst Mode Frequency vs Output Current 20 OUTPUT CURRENT (mA) To enhance efficiency at light loads, the LT8606 enters into low ripple Burst Mode operation, which keeps the output capacitor charged to the desired output voltage while minimizing the input quiescent current and minimizing output voltage ripple. In Burst Mode operation the LT8606 delivers single small pulses of current to the output capacitor followed by sleep periods where the output power is supplied by the output capacitor. While in sleep mode the LT8606 consumes 1.7A. 12 L = 6.8H VIN = 12V VOUT = 3.3V SYNC = 0V 2250 L = 10H VIN = 12V VOUT = 5V RT = 18.2k 15 10 5 0 0 5 10 15 20 25 30 35 INPUT VOLTAGE (V) 40 45 8606 F02 Figure2. Full Switching Frequency Minimum Load vs VIN in Pulse Skipping Mode (MSOP ONLY) SW 5V/DIV VOUT 20mV/DIV ILOAD 100mA/DIV 2s/DIV 8606 F03 Figure3. Burst Mode Operation While a clock is applied to the SYNC pin the LT8606 will also operate in pulse-skipping mode. The LT8606 DFN is always programmed for Burst Mode operation and cannot enter pulse-skipping mode. The LT8606B DFN is programmed for pulse-skipping mode and cannot enter Burst Mode operation. Rev. D For more information www.analog.com LT8606/LT8606B APPLICATIONS INFORMATION FB Resistor Network Operating Frequency Selection and Trade-Offs The output voltage is programmed with a resistor divider between the output and the FB pin. Choose the resistor values according to: Selection of the operating frequency is a trade-off between efficiency, component size, and input voltage range. The advantage of high frequency operation is that smaller inductor and capacitor values may be used. The disadvantages are lower efficiency and a smaller input voltage range. V R1= R2 OUT - 1 0.778V 1% resistors are recommended to maintain output voltage accuracy. The total resistance of the FB resistor divider should be selected to be as large as possible when good low load efficiency is desired: The resistor divider generates a small load on the output, which should be minimized to optimize the quiescent current at low loads. When using large FB resistors, a 10pF phase lead capacitor should be connected from VOUT to FB. Setting the Switching Frequency The LT8606 uses a constant frequency PWM architecture that can be programmed to switch from 200kHz to 2.2MHz by using a resistor tied from the RT pin to ground. A table showing the necessary RT value for a desired switching frequency is in Table1. When in spread spectrum modulation mode, the frequency is modulated upwards of the frequency set by RT. Table1. SW Frequency vs RT Value The highest switching frequency (fSW(MAX)) for a given application can be calculated as follows: fSW(MAX) = ( VOUT + VSW(BOT) t ON(MIN) VIN - VSW(TOP) + VSW(BOT) ) where VIN is the typical input voltage, VOUT is the output voltage, VSW(TOP) and VSW(BOT) are the internal switch drops (~0.13V, ~0.06V, respectively at max load) and tON(MIN) is the minimum top switch on-time (see Electrical Characteristics). This equation shows that slower switching frequency is necessary to accommodate a high VIN/ VOUT ratio. For transient operation VIN may go as high as the Abs Max rating regardless of the RT value, however the LT8606 will reduce switching frequency as necessary to maintain control of inductor current to assure safe operation. The LT8606 is capable of maximum duty cycle approaching 100%, and the VIN to VOUT dropout is limited by the RDS(ON) of the top switch. In this mode the LT8606 skips switch cycles, resulting in a lower switching frequency than programmed by RT. fSW (MHz) RT (k) 0.2 221 0.300 143 0.400 110 0.500 86.6 0.600 71.5 0.700 60.4 0.800 52.3 0.900 46.4 1.000 40.2 1.200 33.2 1.400 27.4 1.600 23.7 1.800 20.5 2.000 18.2 2.200 16.2 where VIN(MIN) is the minimum input voltage without skipped cycles, VOUT is the output voltage, VSW(TOP) and VSW(BOT) are the internal switch drops (~0.13V, ~0.06V, respectively at max load), fSW is the switching frequency (set by RT), and tOFF(MIN) is the minimum switch offtime. Note that higher switching frequency will increase the minimum input voltage below which cycles will be dropped to achieve higher duty cycle. For applications that cannot allow deviation from the programmed switching frequency at low VIN/VOUT ratios use the following formula to set switching frequency: VIN(MIN) = VOUT + VSW(BOT) 1- fSW * t OFF(MIN) - VSW(BOT) + VSW(TOP) Rev. D For more information www.analog.com 13 LT8606/LT8606B APPLICATIONS INFORMATION Inductor Selection and Maximum Output Current The LT8606 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 LT8606 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 *4 where fSW is the switching frequency in MHz, VOUT is the output voltage, VSW(BOT) is the bottom switch drop (~0.06V) and L is the inductor value in H. To avoid overheating and poor efficiency, an inductor must be chosen with an RMS current rating that is greater than the maximum expected output load of the application. In addition, the saturation current (typically labeled ISAT) rating of the inductor must be higher than the load current plus 1/2 of in inductor ripple current: 1 IL(PEAK) =ILOAD(MAX) + L 2 where IL is the inductor ripple current as calculated several paragraphs below and ILOAD(MAX) is the maximum output load for a given application. As a quick example, an application requiring 0.25A output should use an inductor with an RMS rating of greater than 0.5A and an ISAT of greater than 0.7A. To keep the efficiency high, the series resistance (DCR) should be less than 0.04, and the core material should be intended for high frequency applications. The LT8606 limits the peak switch current in order to protect the switches and the system from overload faults. The top switch current limit (ILIM) is at least 0.65A at low duty cycles and decreases linearly to at least 0.5A 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: I IOUT(MAX) =ILIM - L 2 14 The peak-to-peak ripple current in the inductor can be calculated as follows: IL = VOUT V 1- OUT L * fSW VIN(MAX) where fSW is the switching frequency of the LT8606, and L is the value of the inductor. Therefore, the maximum output current that the LT8606 will deliver depends on 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. The optimum inductor for a given application may differ from the one indicated by this design guide. A larger value inductor provides a higher maximum load current and reduces the output voltage ripple. For applications requiring smaller load currents, the value of the inductor may be lower and the LT8606 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 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. Input Capacitor Bypass the input of the LT8606 circuit with a ceramic capacitor of X7R or X5R type. Y5V types have poor performance over temperature and applied voltage, and should not be used. A 4.7F to 10F ceramic capacitor is adequate to bypass the LT8606 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 Rev. D For more information www.analog.com LT8606/LT8606B APPLICATIONS INFORMATION inductance due to long wires or cables, additional bulk capacitance may be necessary. This can be provided with a low performance electrolytic capacitor. Step-down regulators draw current from the input supply in pulses with very fast rise and fall times. The input capacitor is required to reduce the resulting voltage ripple at the LT8606 and to force this very high frequency switching current into a tight local loop, minimizing EMI. A 4.7F capacitor is capable of this task, but only if it is placed close to the LT8606 (see the PCB Layout section). A second precaution regarding the ceramic input capacitor concerns the maximum input voltage rating of the LT8606. A ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. If the LT8606 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT8606'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 LT8606 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 LT8606's control loop. Ceramic capacitors have very low equivalent series resistance (ESR) and provide the best ripple performance. A good starting value is: C OUT = 100 VOUT * fSW can be used to save space and cost but transient performance will suffer and may cause loop instability. See the Typical Applications in this data sheet for suggested capacitor values. When choosing a capacitor, special attention should be given to the data sheet to calculate the effective capacitance under the relevant operating conditions of voltage bias and temperature. A physically larger capacitor or one with a higher voltage rating may be required. Ceramic Capacitors Ceramic capacitors are small, robust and have very low ESR. However, ceramic capacitors can cause problems when used with the LT8606 due to their piezoelectric nature. When in Burst Mode operation, the LT8606's switching frequency depends on the load current, and at very light loads the LT8606 can excite the ceramic capacitor at audio frequencies, generating audible noise. Since the LT8606 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 LT8606. As previously mentioned, a ceramic input capacitor combined with trace or cable inductance forms a high quality (under damped) tank circuit. If the LT8606 circuit is plugged into a live supply, the input voltage can ring to twice its nominal value, possibly exceeding the LT8606's rating. This situation is easily avoided (see Analog Devices Application Note 88). Enable Pin where fSW is in MHz, and COUT is the recommended output capacitance in F. Use X5R or X7R types. This choice will provide low output ripple and good transient response. Transient performance can be improved with a higher value output capacitor and the addition of a feedforward capacitor placed between VOUT and FB. Increasing the output capacitance will also decrease the output voltage ripple. A lower value of output capacitor The LT8606 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 VIN if the shutdown feature is not used, or tied to a logic level if shutdown control is required. Adding a resistor divider from VIN to EN programs the LT8606 to regulate the output only when VIN is above a desired voltage (see Block Diagram). Typically, this threshold, VIN(EN), is used in situations where the input Rev. D For more information www.analog.com 15 LT8606/LT8606B APPLICATIONS INFORMATION supply is current limited, or has a relatively high source resistance. A switching regulator draws constant power from the source, so source current increases as source voltage drops. This looks like a negative resistance load to the source and can cause the source to current limit or latch low under low source voltage conditions. The VIN(EN) threshold prevents the regulator from operating at source voltages where the problems might occur. This threshold can be adjusted by setting the values R3 and R4 such that they satisfy the following equation: R3 VIN(EN) = +1 *1V R4 where the LT8606 will remain off until VIN is above VIN(EN). Due to the comparator's hysteresis, switching will not stop until the input falls slightly below VIN(EN). When in Burst Mode operation for light-load currents, the current through the VIN(EN) resistor network can easily be greater than the supply current consumed by the LT8606. 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 LT8606's circuitry and must be bypassed to ground with a minimum of 1F ceramic capacitor. Good bypassing is necessary to supply the high transient currents required by the power MOSFET gate drivers. Applications with high input voltage and high switching frequency will increase die temperature because of the higher power dissipation across the LDO. Do not connect an external load to the INTVCC pin. Output Voltage Tracking and Soft-Start (MSOP ONLY) The LT8606 allows the user to program its output voltage ramp rate by means of the TR/SS pin. An internal 2A pulls up the TR/SS pin to INTVCC. Putting an external capacitor on TR/SS enables soft-starting the output to prevent current surge on the input supply. During the softstart ramp the output voltage will proportionally track the 16 TR/SS pin voltage. For output tracking applications, TR/ SS can be externally driven by another voltage source. From 0V to 0.778V, the TR/SS voltage will override the internal 0.778V reference input to the error amplifier, thus regulating the FB pin voltage to that of TR/SS pin. When TR/SS is above 0.778V, tracking is disabled and the feedback voltage will regulate to the internal reference voltage. An active pull-down circuit is connected to the TR/SS pin which will discharge the external soft-start capacitor in the case of fault conditions and restart the ramp when the faults are cleared. Fault conditions that clear the soft-start capacitor are the EN/UV pin transitioning low, VIN voltage falling too low, or thermal shutdown. The LT8606 and LT8606B DFN does not have TR/SS pin or functionality. Output Power Good When the LT8606'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 (MSOP ONLY) 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 LT8606 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 LT8606 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 LT8606 may be synchronized over a 200kHz to 2.2MHz range. The RT resistor should be chosen to set the LT8606 switching frequency equal to or below the lowest synchronization Rev. D For more information www.analog.com LT8606/LT8606B APPLICATIONS INFORMATION input. For example, if the synchronization signal will be 500kHz and higher, the RT should be selected for 500kHz. The slope compensation is set by the RT value, while the minimum slope compensation required to avoid subharmonic oscillations is established by the inductor size, input voltage, and output voltage. Since the synchronization frequency will not change the slopes of the inductor current waveform, if the inductor is large enough to avoid subharmonic oscillations at the frequency set by RT, then the slope compensation will be sufficient for all synchronization frequencies. For some applications it is desirable for the LT8606 to operate in pulse-skipping mode, offering two major differences from Burst Mode operation. First is the clock stays awake at all times and all switching cycles are aligned to the clock. Second is that full switching frequency is reached at lower output load than in Burst Mode operation as shown in Figure2. Full Switching Frequency Minimum Load vs VIN in Pulse Skipping Mode (MSOP ONLY) in an earlier section. These two differences come at the expense of increased quiescent current. To enable pulse-skipping mode the SYNC pin is floated. For some applications, reduced EMI operation may be desirable, which can be achieved through spread spectrum modulation. This mode operates similar to pulse skipping mode operation, with the key difference that the switching frequency is modulated up and down by a 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 LT8606 does not operate in forced continuous mode regardless of SYNC signal. The LT8606 DFN is always programmed for Burst Mode operation and cannot enter pulse-skipping mode. The LT8606B DFN is programmed for pulse-skipping mode and cannot enter Burst Mode operation. will be folded back while the output is lower than the set point to maintain inductor current control. Second, the bottom switch current is monitored such that if inductor current is beyond safe levels switching of the top switch will be delayed until such time as the inductor current falls to safe levels. This allows for tailoring the LT8606 to individual applications and limiting thermal dissipation during short circuit conditions. Frequency foldback behavior depends on the state of the SYNC pin: If the SYNC pin is low, 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, tied high or floated, the LT8606 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 LT8606 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 LT8606's output. If the VIN pin is allowed to float and the EN pin is held high (either by a logic signal or because it is tied to VIN), then the LT8606's internal circuitry will pull its quiescent current through its SW pin. This is acceptable if the system can tolerate several A in this state. If the EN pin is grounded the SW pin current will drop to near 0.7A. However, if the VIN pin is grounded while the output is held high, regardless of EN, parasitic body diodes inside the LT8606 can pull current from the output through the SW pin and the VIN pin. Figure4 shows a connection of the VIN and EN/UV pins that will allow the LT8606 to run only when the input voltage is present and that protects against a shorted or reversed input. D1 VIN VIN LT8606 EN/UV GND Shorted and Reversed Input Protection 8606 F04 The LT8606 will tolerate a shorted output. Several features are used for protection during output short-circuit and brownout conditions. The first is the switching frequency Figure4. Reverse VIN Protection Rev. D For more information www.analog.com 17 LT8606/LT8606B APPLICATIONS INFORMATION PCB Layout For proper operation and minimum EMI, care must be taken during printed circuit board layout. Note that large, switched currents flow in the LT8606's VIN pins, GND pins, and the input capacitor (CIN). The loop formed by the input capacitor should be as small as possible by placing the capacitor adjacent to the VIN and GND pins. When using a physically large input capacitor the resulting loop may become too large in which case using a small case/value capacitor placed close to the VIN and GND pins plus a larger capacitor further away is preferred. These components, along with the inductor and output capacitor, should be placed on the same side of the circuit board, and their connections should be made on that layer. Place a local, unbroken ground plane under the application circuit on the layer closest to the surface layer. The SW and BOOST nodes should be as small as possible. Finally, keep the FB and RT nodes small so that the ground traces will shield them from the SW and BOOST nodes. The exposed pad on the bottom of the package must be soldered to ground so that the pad is connected to ground electrically and also acts as a heat sink thermally. To keep thermal resistance low, extend the ground plane as much as possible, and add thermal vias under and near the LT8606 to additional ground planes within the circuit board and on the bottom side. Thermal Considerations For higher ambient temperatures, care should be taken in the layout of the PCB to ensure good heat sinking of the LT8606. Figure5 shows the recommended component placement with trace, ground plane and via locations. The exposed pad on the bottom of the package must be soldered to a ground plane. This ground should be tied to large copper layers below with thermal vias; these layers will spread heat dissipated by the LT8606. Placing additional vias can reduce thermal resistance further. The maximum load current should be derated as the ambient temperature approaches the maximum junction rating. Power dissipation within the LT8606 can be estimated by calculating the total power loss from an efficiency measurement and subtracting the inductor loss. The die temperature is calculated by multiplying the LT8606 power dissipation by the thermal resistance from junction to ambient. The LT8606 will stop switching and indicate a fault condition if safe junction temperature is exceeded. GROUND PLANE ON LAYER 2 COUT L CIN CBST CVCC 1 CIN(OPT) RT RPG R4 R3 R1 CFF GND VIA VIN VIA VOUT VIA EN/UV VIA R2 CSS OTHER SIGNAL VIA 8606 F05 Figure5. PCB Layout 18 Rev. D For more information www.analog.com LT8606/LT8606B TYPICAL APPLICATIONS 5V 2MHz Step Down VIN 5.5V TO 42V VIN EN/UV SYNC C2 1F X7R 0805 INTVCC C3 1F C6 10nF BST C1 0.1F SW LT8606 R4 100k PG C5 10pF TR/SS RT R1 18.2k GND FB fSW = 2MHz L1 10H R3 187k R2 1M L1 = XFL3010-103ME 8606 TA02 VOUT 5V 350mA POWER GOOD C4 10F X7R 0805 3.3V 2MHz Step Down VIN 3.8V TO 42V VIN EN/UV SYNC C2 1F X7R 0805 INTVCC C3 1F C6 10nF BST L1 C1 0.1F 6.8H SW LT8606 R4 100k PG C5 10pF TR/SS RT R1 18.2k GND FB fSW = 2MHz R3 309k R2 1M L1 = XFL3010-682ME 8606 TA03 VOUT 3.3V 350mA POWER GOOD C4 10F X7R 0805 12V 1MHz Step Down VIN 12.7V TO 42V VIN EN/UV SYNC C2 4.7F X7R 1206 INTVCC C3 1F C6 10nF fSW = 1MHz BST C1 0.1F SW LT8606 R4 100k PG C5 100pF TR/SS RT R1 40.2k GND L1 47H FB R3 69.8k R2 1M L1 = MSS6132-473MLB 8606 TA04 VOUT 12V 350mA POWER GOOD C4 22F X7R 1210 Rev. D For more information www.analog.com 19 LT8606/LT8606B TYPICAL APPLICATIONS 1.8V 2MHz Step Down VIN 3.2V TO 20V (42V TRANSIENT) VIN EN/UV SYNC C2 4.7F INTVCC C3 1F C6 10nF BST L1 C1 0.1F 3.3H SW LT8606 R4 100k PG C5 10pF TR/SS RT R1 18.2k GND FB fSW = 2MHz R3 768k R2 1M L1 = XFL3010-332ME 8606 TA05 VOUT 1.8V 350mA POWER GOOD C4 22F X7R 1206 Ultralow EMI 5V 1.5A Step Down VIN 5.8 TO 40V L2 BEAD L3 4.7H C8 4.7F C7 4.7F C9 33F VIN EN/UV SYNC C2 4.7F INTVCC C3 1F C6 10nF fSW = 700kHz 20 BST C1 0.1F SW LT8606 (MSOP) PG GND FB R4 100k C5 47pF TR/SS RT R1 60.4k L1 27H R3 187k R2 1M C8, C7, C2: X7R 1206 C9: 63SXV33M L1: MSS5121-273 L2: MPZ2012S221AT000 L3: XAL4030-472 8606 TA06 VOUT 5V 350mA POWER GOOD C4 22F X7R 1206 Rev. D For more information www.analog.com LT8606/LT8606B PACKAGE DESCRIPTION MSE Package 10-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1664 Rev I) BOTTOM VIEW OF EXPOSED PAD OPTION 1.88 0.102 (.074 .004) 5.10 (.201) MIN 1 0.889 0.127 (.035 .005) 1.68 0.102 (.066 .004) 0.05 REF 10 0.305 0.038 (.0120 .0015) TYP RECOMMENDED SOLDER PAD LAYOUT 3.00 0.102 (.118 .004) (NOTE 3) DETAIL "B" CORNER TAIL IS PART OF DETAIL "B" THE LEADFRAME FEATURE. FOR REFERENCE ONLY NO MEASUREMENT PURPOSE 10 9 8 7 6 DETAIL "A" 0 - 6 TYP 1 2 3 4 5 GAUGE PLANE 0.53 0.152 (.021 .006) DETAIL "A" 0.18 (.007) 0.497 0.076 (.0196 .003) REF 3.00 0.102 (.118 .004) (NOTE 4) 4.90 0.152 (.193 .006) 0.254 (.010) 0.29 REF 1.68 (.066) 3.20 - 3.45 (.126 - .136) 0.50 (.0197) BSC 1.88 (.074) SEATING PLANE 0.86 (.034) REF 1.10 (.043) MAX 0.17 -0.27 (.007 - .011) TYP 0.50 (.0197) BSC 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. 0.1016 0.0508 (.004 .002) MSOP (MSE) 0213 REV I Rev. D For more information www.analog.com 21 LT8606/LT8606B PACKAGE DESCRIPTION DC8 Package 8-Lead Plastic DFN (2mm x 2mm) (Reference LTC DWG # 05-08-1939 Rev O) Exposed Pad Variation AA 1.8 REF 0.90 REF 0.23 REF 0.85 0.05 2.60 0.05 PACKAGE OUTLINE 0.335 REF 0.25 0.05 0.45 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 2.00 0.05 (4 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6) 2.00 SQ 0.05 1.8 REF 5 8 0.23 0.335 REF REF 0.55 0.05 PIN 1 NOTCH R = 0.15 (DC8MA) DFN 0113 REV O 4 0.200 REF 0.75 0.05 1 0.23 0.05 0.45 BSC BOTTOM VIEW--EXPOSED PAD 0.00 - 0.05 NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. 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 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 22 Rev. D For more information www.analog.com LT8606/LT8606B REVISION HISTORY REV DATE DESCRIPTION A 06/17 Added DFN package option 1,2 Clarified electrical parameters for DFN package option 2,3 Clarified graphs for MSOP package option 6,7 Clarified Pin Functions for DFN package option 9 Clarified Operation section to include DFN option 11 Clarified Applications last paragraph and Figure 2 to include DFN option 12 Clarified Applications section to include DFN operation B 11/17 07/18 22 Added H-grade option 2, 3 Clarified Oscillator Frequency RT conditions 3 Clarified efficiency graphs 4 Clarified Frequency Foldback graph 7 Clarified Switching Waveform graph 8 Clarified Block Diagram 10 Added Figure 5 18 All Added table to clarify versions 1 Modified text in Description to add DFN functionality 1 Added B version to Order Information 2 Clarified Minimum On-Time Conditions 3 Clarified Efficiency graphs 4 Clarified No-Load Supply Current graphs 5 Clarified Burst Frequency vs Output Current graph 6 Clarified Frequency Foldback graph 7 Clarified Pin Functions on SYNC and TR/SS 9 Clarified Operation third paragraph 11 Clarified Applications Information to include DFN B version 11/20 20, 24 Added B version Clarified last paragraph to include DFN B version D 16,17 Added DFN Package Description Clarified Typical Applications for MSOP package option C PAGE NUMBER 12 16, 17 Clarified Figure 5 PCB Layout 18 AEC-Q100 Qualified for Automotive Applications 1 Added J-Grade to Operating Junction 2 Updated suffix for DC package 2 #W Materials added on 2 Changed Minimum On-Time conditions in the Electrical Characteristics table 3 Rev. D Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license For is granted implication or otherwise under any patent or patent rights of Analog Devices. more by information www.analog.com 23 LT8606/LT8606B TYPICAL APPLICATION 5V and 3.3V with Ratio Tracking VIN 5.6V TO 42V BST VIN EN/UV SYNC C2 1F INTVCC C3 1F SW LT8606 (MSOP) C1 0.1F R1 18.2k RT GND PG FB VOUT 5V 350mA R4 100k POWER GOOD C5, 10pF TR/SS C6 10nF L1 10H R3 187k R2, 1M C4 10F fSW = 2MHz C8 1F R9 80.6k C2, C4, C8, C10: X7R 0805 L1: XFL3010-103ME L2: XFL3010-682ME R10 22k C12 1F R5 18.2k VIN EN/UV SYNC INTVCC BST SW LT8606 (MSOP) L2 C1 0.1F 6.8H PG GND FB POWER GOOD C11, 10pF TR/SS RT VOUT 3.3V 350mA R8 100k R7 309k fSW = 2MHz R6, 1M C10 10F 8606 TA07 RELATED PARTS PART NUMBER LT8607 LT8608 LT8609/LT8609A/ LT8609B LT8609S LT8610A/ LT8610AB/LT8610AC LT8616 LT8620 LT8614 LT8612 LT8640 LT8640S LT8645S LT8602 24 DESCRIPTION 42V, 750mA, 92% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with IQ=3A 42V, 1.5A, 92% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with IQ=2.5A 42V, 2A/3A Peak, 93% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with IQ=2.5A 42V, 2A/3A Peak, 93% Efficiency, 2.2MHz Synchronous Silent Switcher2 Step-Down DC/DC Converter with IQ=2.5A 42V, 3.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with IQ=2.5A 42V, Dual 2.5A + 1.5A, 95% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with IQ=5A 65V, 2.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with IQ=2.5A 42V, 4A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with IQ=2.5A 42V, 6A, 96% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with IQ=2.5A 42V, 5A, 96% Efficiency, 3MHz Synchronous MicroPower Step-Down DC/DC Converter with IQ=2.5A 42V, 6A, 96% Efficiency, 3MHz Synchronous Silent Switcher2 Step-Down DC/DC Converter with IQ=2.5A 65V, 8A, 96% Efficiency, 3MHz Synchronous Silent Switcher 2 Step-Down DC/DC Converter with IQ=2.5A 42V, Quad Output (2.5A+1.5A+1.5A+1.5A) 95% Efficiency, 2.2MHz Synchronous MicroPower Step-Down DC/DC Converter with IQ=25A COMMENTS VIN=3Vto42V, VOUT(MIN)=0.778V, IQ=3A, ISD<1A, MSOP-10E Package VIN=3Vto42V, VOUT(MIN)=0.778V, IQ=2.5A, ISD<1A, MSOP-10E Package VIN=3Vto42V, VOUT(MIN)=0.782V, IQ=2.5A, ISD<1A, MSOP-10E Package VIN=3Vto42V, VOUT(MIN)=0.774V, IQ=2.5A, ISD<1A, 3mmx3mm LQFN-16 Package VIN=3.4Vto42V, VOUT(MIN)=0.97V, IQ=2.5A, ISD<1A, MSOP-16E Package VIN=3.4V to42V, VOUT(MIN)=0.8V, IQ=5A, ISD<1A, TSSOP-28E, 3mmx6mm QFN-28 Packages VIN=3.4V to65V, VOUT(MIN)=0.97V, IQ=2.5A, ISD<1A, MSOP-16E, 3mmx5mm QFN-24 Packages VIN=3.4V to42V, VOUT(MIN)=0.97V, IQ=2.5A, ISD<1A, 3mmx4mm QFN-18 Package VIN=3.4V to42V, VOUT(MIN)=0.97V, IQ=3.0A, ISD<1A, 3mmx6mm QFN-28 Package VIN=3.4V to42V, VOUT(MIN)=0.97V, IQ=2.5A, ISD<1A, 3mmx4mm QFN-18 Package VIN=3.4V to42V, VOUT(MIN)=0.97V, IQ=2.5A, ISD<1A, 4mmx4mm LQFN-24 Package VIN=3.4V to65V, VOUT(MIN)=0.97V, IQ=2.5A, ISD<1A, 4mmx6mm LQFN-32 Package VIN=3V to42V, VOUT(MIN)=0.8V, IQ=25A, ISD<1A, 6mmx6mm QFN-40 Package Rev. D D17104-0-11/20 www.analog.com For more information www.analog.com ANALOG DEVICES, INC. 2017-2020