Power Management

LT8601

Linear Technology

42V Triple Monolithic Synchronous Step-Down Regulator

Manufacturer: Linear Technology

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8601faFor more information www.linear .com/L T8601 Typical applicaTion FeaTures DescripTion 42V Triple Monolithic Synchronous Step-Down Regulator The LT®8601 is a triple channel, current mode, monolithic buck switching regulator with a programmable power-on reset. All regulators are synchronized to a single oscillator with an adjustable frequency from 250kHz to 2.2MHz. The LT8601 can be configured for micropower Burst Mode or pulse-skipping operation at light load. Micropower opera- tion results in quiescent current of 30µA with all three regulators operating as shown in the application below with no load applied. The high voltage channels are synchronous buck regula- tors that operate from an input of 3.0V to 42V. The output currents are up to 1.5A (OUT1) and 2.5A (OUT2). The low voltage channel operates from an input of 2.6V to 5.5V. Internal synchronous power switches provide high efficiency with output currents up to 1.8A. The LT8601 uses a 2-phase clock with channel 1 operating 180° from channels 2 and 3 to reduce input ripple current on both HV and LV inputs. All channels have cycle-by-cycle cur - rent limit, providing protection against shorted outputs. Thermal shutdown provides additional protection. The LT8601 is available in a 40-lead 6mm × 6mm QFN package. Automotive Input Stepped Down to 5V, 3.3V and 1.8V Outputs at 2MHz

applicaTions

n Flexible Power Supply System Providing Three Outputs Over a Wide Input Voltage Range n T wo High Voltage Synchronous Buck Regulators n 3V to 42V Input Voltage Range n Output Currents Up to 2.5A and 1.5A n High Efficiency Up to 93% n One Low Voltage Synchronous Buck Regulator n 2.6V to 5.5V Input Voltage Range n Output Current Up to 1.8A and 95% Efficiency n Resistor Programmable and Synchronizable from 250kHz to 2.2MHz Switching Frequency n Low Ripple Burst Mode® Operation n 30µA IQ at 12VIN to 3.3VOUT2 n Output Ripple < 15mV n Programmable Power-On Reset n Power Good Indicators n 2-Phase Clock Reduces Input Current Ripple n Available in Thermally Enhanced 40-Lead QFN (6mm × 6mm) Package n Automotive Systems n Distributed Supply Regulation n Industrial Controls and Power Supplies L, L T , L TC, L TM, Linear Technology, the Linear logo and Burst Mode are registered trademarks of Analog Devices, Inc. All other trademarks are the property of their respective owners. HV Channel Efficiency, VOUT1 = 5V LV Channel Efficiency, V OUT3 = 1.8V

8601 TA01a

6V TO 24V , TRANSIENTS TO 42V L T8601 POREN PVIN1 PVIN2 EN/UVLO OUT3 1.8V , 1.8ASW3 FB3 BST1 OUT1 5V , 1.5A SW1 FB1 BST2 OUT2 3.3V , 1A* SW2 FB2BIAS PVIN3 INTVCC CPOR TRKSS1, 2 RT SYNC RST PG1-3 RUN3 3.3/uni03BCH 1/uni03BCH 1/uni03BCH 22/uni03BCF 47/uni03BCF 22/uni03BCF *IMAX = 2.5A – IPVIN3 – IBIAS OUT2 EFFICIENCY f SW = 1MHz f SW = 2MHz LOAD CURRENT (A) 0.3 0.6 0.9 1.2 1.5 100 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 EFFICIENCY (%) POWER LOSS (W) POWER LOSS

8601 TA01b

VIN = 12V LOAD CURRENT (A) 0.3 0.6 0.9 1.2 1.5 1.8 100 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 EFFICIENCY (%) POWER LOSS (W)

8601 TA01c

f SW = 1MHz f SW = 2MHz POWER LOSS

8601fa For more information www.linear .com/L T8601 pin conFiguraTionabsoluTe MaxiMuM raTings Supply Voltages PG1-3, SYNC, TRKSS1-2, RT .6V B 3V to 15V Operating Junction Temperature (Notes 2 and 3) (Note 1) 3940 38 37 36 35 34 33 32 31 11 2012 13 14 15 TOP VIEW GND UJ PACKAGE 40-LEAD (6mm × 6mm) PLASTIC QFN 16 17 18 19 PG1 GND SW1 BST1 BST2 SW2 SW2 GND GND BIAS GND RT INTV CC GND FB1 FB2 FB3 V IN EN/UVLO TRKSS1 GND POREN GND PV IN1 NC GND GND SYNC RST CPOR PG2 PG3 GND PV IN2 SW3 GND PVIN3 RUN3 NC TRKSS2 θJA = 33°C/W , θJC = 2°C/W EXPOSED PAD (PIN 41) IS GND, MUST BE SOLDERED TO PCB orDer inForMaTion LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT8601EUJ#PBF LT8601EUJ#TRPBF LT8601 40-Lead (6mm × 6mm) Plastic QFN –40°C to 125°C LT8601IUJ#PBF LT8601IUJ#TRPBF LT8601 40-Lead (6mm × 6mm) Plastic QFN –40°C to 125°C Consult L TC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container . For more information on lead free part marking, go to: http://www.linear .com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear .com/tapeandreel/. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix. http://www.linear .com/product/LT8601#orderinfo

8601faFor more information www.linear .com/L T8601

elecTrical characTerisTics

PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum Operating Voltage l 2.7 3 V Minimum Operating Voltage to Start l 3.1 3.5 V VIN Quiescent Current, Shutdown EN/UVLO = 0.4V 0.1 1 µA VIN Quiescent Current, Operating All Channels Active, No Load (Note 4) All Channels Active,100µA on VOUT2 (Note 4) µA µA EN/UVLO Threshold EN/UVLO Rising EN/UVLO Falling l l 1.15 1.0 1.2 1.15 1.25 1.2 V V EN/UVLO Input Current EN/UVLO = 1.2V, VIN = 42V −40 40 nA Oscillator Switching Frequency RT = 28.7k l 1.8 2 2.2 MHz RT = 254k l 0.225 0.25 0.275 MHz SYNC Input Frequency Range l 0.25 2.2 MHz SYNC Input Voltage Low l 0.3 V SYNC Input Voltage High l 1.2 V SYNC Input Current −100 100 nA Channel 1 Feedback Voltage l 0.988 1 1.012 V Input Current FB1 l −100 100 nA FB1 Voltage Line Regulation VIN = 3V to 42V 0.002 0.01 %/V SW1 Peak Current Limit VIN = PVIN1 = PVIN2 = 6V 2.3 2.7 3.0 A SW1 Leakage Current 0.1 1 µA SW1 Top On Resistance ISW1 = 1A 240 mΩ SW1 Bottom On Resistance ISW1 = 1A 170 mΩ Lower FB1 Power Good Threshold Percentage of VFB1 l 89 92 95 % Upper FB1 Power Good Threshold Percentage of VFB1 l 105 108 111 % PG1 Output Voltage Low IPG1 = –350μA l 0.13 0.3 V PG1 Leakage Current PG1 = 5V, FB1 = 1V l 30 μA TRKSS1 Pull-Up Current TRKSS1 = 0.2V 1.5 2.4 3.1 μA Minimum Switch-On Time ISW1 = 1A 60 ns Minimum Switch-Off Time ISW1 = 1A 70 ns Channel 2 Feedback Voltage l 0.988 1 1.012 V Input Current FB2 l −100 100 nA FB2 Voltage Line Regulation VIN = 3V to 42V 0.002 0.01 %/V SW2 Peak Current Limit VIN = PVIN1 = PVIN2 = 6V 3.5 4.0 4.5 A SW2 Leakage Current 0.1 1 µA SW2 Top On Resistance ISW2 = 1A 150 mΩ SW2 Bottom On Resistance ISW2 = 1A 100 mΩ Lower FB2 Power Good Threshold Percentage of VFB2 l 89 92 95 % Upper FB2 Power Good Threshold Percentage of VFB2 l 105 108 111 % PG2 Output Voltage Low IPG2 = –350µA l 0.13 0.3 V The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = PVIN1 = PVIN2 = 12V, EN/UVLO = 3V, PVIN3 = 3.3V unless otherwise noted. (Note 2)

8601fa For more information www.linear .com/L T8601 elecTrical characTerisTics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = PVIN1 = PVIN2 = 12V, EN/UVLO = 3V, PVIN3 = 3.3V unless otherwise noted. (Note 2) PARAMETER CONDITIONS MIN TYP MAX UNITS PG2 Leakage Current PG2 = 5V, FB2 = 1V l 30 µA TRKSS2 Pull-Up Current TRKSS2 = 0.2V 1.5 2.4 3.1 µA Minimum Switch-On Time ISW2 = 2A 55 ns Minimum Switch-Off Time ISW2 = 2A 70 ns Channel 3 Operating Voltage l 2.6 5.5 V Feedback Voltage l 790 800 810 mV Input Current FB3 l –100 100 nA FB3 Voltage Line Regulation VIN = 3V to 42V 0.002 0.01 %/V SW3 Current Limit 2.6 3.2 3.8 A SW3 Leakage PVIN3 = 5.5V 0.1 1 µA SW3 PMOS On Resistance ISW3 = 1A 150 mΩ SW3 NMOS On Resistance ISW3 = 1A 120 mΩ Lower FB3 Power Good Threshold Percentage of VFB3 l 89 92 95 % Upper FB3 Power Good Threshold Percentage of VFB3 l 105 108 111 % PG3 Output Voltage Low IPG3 = –350μA l 0.13 0.3 V PG3 Leakage Current PG3 = 5V, FB3 = 0.8V l 30 µA RUN3 Threshold Voltage l 0.695 0.72 0.74 V RUN3 Input Current RUN3 = 3.3V l –100 100 nA Soft-Start Time l 0.7 1 1.3 ms Minimum Switch-On Time ISW3 = 1A 70 ns Minimum Switch-Off Time ISW3 = 1A 70 ns PVIN3 UVLO l 2.35 2.6 V Power-On Reset CPOR Pull-Up Current CPOR = 0V 2 μA POR Delay Time CPOR = 1000pF l 31 35.2 39.4 ms RST Output Voltage Low IRST = –100μA l 0.1 0.2 V RST Pull-Up Current POR Timed Out, RST = 0V 20 μA RST Leakage Current RST = 6V, EN/UVLO = 0V –40 40 nA POREN Threshold l 1.15 1.2 1.25 V POREN Pull-Up Current POREN = 0V 0.8 1.2 1.6 μA 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. Note 2: The LT8601E 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 LT8601I is guaranteed to meet performance specifications from –40°C to 125°C junction temperature. High junction temperatures degrade operating lifetimes. Operating lifetime is derated at junction temperatures above 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 junction temperature will reduce lifetime. Note 4: All three channels enabled as shown in the application circuit titled, “Details of the Front Page Application” (using the 1MHz component values) found in the Typical Application section.

8601faFor more information www.linear .com/L T8601 Channel 2 Peak Current Limit vs Duty Cycle Channel 3 Peak Current Limit vs Duty Cycle Typical perForMance characTerisTics Quiescent Current vs VIN Channel 1 Peak Current Limit vs Duty Cycle Channel 1 Efficiency vs Load V OUT1 = 8V, fSW = 2MHz Channel 2 Efficiency vs Load V OUT2 = 3.3V, fSW = 2MHz Channel 2 Efficiency vs Load V OUT2 = 3.3V, fSW = 1MHz LV Channel Efficiency vs Load V OUT3 = 1.8V, fSW = 1MHz LV Channel Efficiency vs Load V OUT3 = 1.2V,fSW = 2MHz TA = 25°C, VIN = PVIN1 = PVIN2 = 12V, EN/UVLO = 3V and PVIN3 = 3.3V, unless otherwise noted. V IN (V) IQ (µA)

8601 G06

= 12V PV IN1 = 28V PV IN1 = 42V LOAD CURRENT (A) 0.0001 0.001 0.01 0.1 100 EFFICIENCY (%) OUT1 SW

8601 G01

= 5.5V PV IN2 = 12V PV IN2 = 24V LOAD CURRENT (A) 0.5 1.5 2.5 100 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0 EFFICIENCY (%) POWER LOSS (W) V OUT2 = 3.3V , f SW = 2MHz

8601 G02

= 2.6V PV IN3 = 3.3V PV IN3 = 5.5V LOAD CURRENT (A) 0.0001 0.001 0.01 0.1 100 EFFICIENCY (%) OUT3 SW

8601 G04

= 2.6V PV IN3 = 3.3V PV IN3 = 5.5V LOAD CURRENT (A) 0.4 0.8 1.2 1.6 100 EFFICIENCY (%) OUT3 SW

8601 G05

DUTY CYCLE (%) 100 1.5 1.8 2.1 2.4 2.7 3.0 TOP FET CURRENT LIMIT (A) Duty Cycle

8601 G07

DUTY CYCLE (%) 100 2.5 3.0 3.5 4.0 4.5 5.0 TOP FET CURRENT LIMIT (A)

8601 G08

DUTY CYCLE (%) 100 1.5 2.0 2.5 3.0 3.5 4.0 TOP FET CURRENT LIMIT (A) Duty Cycle

8601 G09

= 5.5V PV IN2 = 12V PV IN2 = 28V LOAD CURRENT (A) 0.0001 0.001 0.01 0.1 100 EFFICIENCY (%) V OUT2 = 3.3V , f SW = 1MHz

8601 G03

8601fa For more information www.linear .com/L T8601 Typical perForMance characTerisTics Full Frequency Waveforms Light Load Waveforms TRKSS Pull-Up Current vs Voltage RST Pull-Up Current vs Voltage Power-On Reset Time vs CPOR Switching Frequency vs RT TA = 25°C, VIN = PVIN1 = PVIN2 = 12V, EN/UVLO = 3V and PVIN3 = 3.3V, unless otherwise noted. Switching Frequency vs Temperature Minimum On-Time vs ISW Minimum Off-Time vs ISW TEMPERATURE (°C) –10 –30 –50 110 130 150 FREQUENCY CHANGE (%)

8601 G10

RT = 30k RT = 60k RT = 250k RST VOL TAGE (V) 0.5 1.5 2.5 3.5 –30 –20 –10 RST CURRENT (µA)

8601 G12

CPOR (pF) 2000 4000 6000 8000 10000 100 150 200 250 350 300 400 POR DELAY TIME (ms)

8601 G13

R T (kΩ) 100 125 150 175 200 225 250 275 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 FREQUENCY (MHz)

8601 G14

V OUT1 = 5V V OUT2 = 3.3V V OUT3 = 1.8V 200ns/DIV V SW1 10V/DIV V SW2 10V/DIV V SW3 2V/DIV

8601 G15

SWITCH CURRENT (A) 0.5 1.5 2.5 100 MINIMUM ON-TIME (ns)

8601 G17

5µs/DIV VOUT 20mV/DIV VSW 5V/DIV CHANNEL 1 12VIN TO 5VOUT AT 10mA VSYNC = 0V IL 0.5A/DIV

8601 G16

SWITCH CURRENT (A) 0.5 1.5 2.5 100 MINIMUM OFF-TIME (ns)

8601 G18

TRKSS VOL TAGE (V) 0.5 1.5 2.5 3.5 TRKSS CURRENT (µA)

8601 G11

8601faFor more information www.linear .com/L T8601 TA = 25°C, VIN = PVIN1 = PVIN2 = 12V, EN/UVLO = 3V and PVIN3 = 3.3V, unless otherwise noted. Channel 3 RDS(ON) vs Temperature Feedback Voltage vs Temperature EN/UVLO Current vs Voltage Channel 3 Minimum Off-Time vs ISW Channel 1 RDS(ON) vs Temperature Channel 2 RDS(ON) vs Temperature Typical perForMance characTerisTics Channel 3 Minimum On-Time vs I SW Minimum On-Time vs Temperature Minimum Off-Time vs Temperature TEMPERATURE (°C) –50 –25 100 125 150 MINIMUM ON-TIME (ns)

8601 G19

I SW = 1A CHANNEL 2 TEMPERATURE (°C) –50 –25 100 125 150 100 MINIMUM OFF-TIME (ns)

8601 G20

I SW = 1A TEMPERATURE (°C) –50 –25 100 125 150 100 200 300 400 500 R DSON (mΩ)

8601 G23

I SW1 = 1A TEMPERATURE (°C) –50 –25 100 125 150 100 200 300 400 R DSON (mΩ)

8601 G24

I SW2 = 1A TEMPERATURE (°C) –50 –25 100 125 150 100 150 200 250 300 R DSON (mΩ)

8601 G25

I SW3 = 1A V EN/UVLO (V) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 I EN/UVLO (µA)

8601 G27

CHANNELS 1, 2 CHANNEL 3 TEMPERATURE (°C) –50 –25 100 125 150 0.990 0.995 1.000 1.005 1.010 0.790 0.795 0.800 0.805 0.810 CHANNELS 1, 2 V FB (V) CHANNEL 3 V FB (V)

8601 G26

= 2.6V PV IN3 = 3.3V PV IN3 = 5.5V I SW (A) 0.2 0.4 0.6 0.8 1.2 1.4 1.6 1.8 108 126 144 162 180 MINIMUM ON–TIME (ns) Channel 3 Minimum On–Time vs I SW

8601 G21

I SW (A) 0.2 0.4 0.6 0.8 1.2 1.4 1.6 1.8 100 MINIMUM OFF–TIME (ns) Channel 3 Minimum Off–Time vs I SW

8601 G22

8601fa For more information www.linear .com/L T8601 TA = 25°C, VIN = PVIN1 = PVIN2 = 12V, EN/UVLO = 3V and PVIN3 = 3.3V, unless otherwise noted. Typical perForMance characTerisTics Channel 2 Start-Up and Dropout, RL = 20Ω Channel 1 Start-Up and Dropout, R L = 20Ω Channel 2 Start-Up and Dropout, R L = 2Ω Channel 1 Start-Up and Dropout, R L = 3.3Ω 100ms/DIV 2V/DIV

8601 G28

8601 G29

8601 G30

8601 G31

Channel 1 Full Frequency VIN vs Load Current Channel 2 Full Frequency VIN vs Load Current Channel 3 Full Frequency VIN vs Load Current R T = 28.7k FULL FREQUENCY REGION (2MHz) V OUT = 3.3V V OUT = 5V I OUT (A) 0.2 0.4 0.6 0.8 1.2 1.4 1.6 V IN (V) Vin vs Load Current

8601 G32

R T = 28.7k FULL FREQUENCY REGION (2MHz) V OUT = 3.3V V OUT = 5V I OUT (A) 0.3 0.7 1.0 1.3 1.6 1.9 2.3 2.6 V IN (V) Vin vs Load Current

8601 G33

R T = 28.7k, V OUT = 1.2V FULL FREQUENCY REGION (2MHz) I OUT (A) 0.2 0.4 0.6 0.8 1.2 1.4 1.6 1.8 2.0 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 V IN (V) Vin vs Load Current

8601 G34

8601faFor more information www.linear .com/L T8601 TA = 25°CTypical perForMance characTerisTics Radiated EMI Performance, CISPR25 Radiated Emission Tests with Class 5 Peak Limit. Vertical Polarization Horizontal Polarization Demo Board with EMI Filter Installed, 14VIN, 1A on All Outputs, fSW = 2MHz. AMPLITUDE (dBµV/m) –15 –10 FREQUENCY (MHz) 0 900100 200 300 500400 600 700 800 1000

8601 EMI 01a

CISPR25 CLASS 5 PEAK LIMIT DATA DETECTOR: +PEAK CISPR25 RADIATED DISTURBANCES – ALSE NOTES: DC2346A AMPLITUDE (dBµV/m) –15 –10 FREQUENCY (MHz) 0 900100 200 300 500400 600 700 800 1000 CISPR25 CLASS 5 PEAK LIMIT DATA DETECTOR: +PEAK CISPR25 RADIATED DISTURBANCES – ALSE NOTES: DC2346A

8601fa For more information www.linear .com/L T8601 pin FuncTions BIAS (Pin 10): Power to the Internal Regulator . Connect to an output ≥ 3.2V when available. Decouple to ground with a low ESR capacitor . BST1, BST2 (Pins 4, 5): Boost Voltage for High Voltage Channels. The Boost Voltage provides a drive voltage higher than PVIN to the gate of the NMOS top switch. CPOR (Pin 31): Power-On Reset Timer . Connect a capaci- tor from this pin to ground to program the power-on reset timer . CPOR has a 2μA (typical) pull-up current. EN/UVLO (Pin 22): Enable/Undervoltage Lockout Input. The LT8601 is in low power shutdown when this pin is ≤ 0.4V. A precision threshold at 1.20V (rising) enables the switching regulator’ s output switching stages. This allows the EN/UVLO pin to be used as an input undervolt- age lockout by connecting to a resistor divider between VIN and GND. When the EN/UVLO voltage is between 0.4V and 1.2V, the LT8601 input current will depend on the mode selected, the VIN voltage, and the EN/UVLO voltage. Connect this pin to VIN if the UVLO function is not needed. FB1, FB2 (Pins 26, 25): Feedback Input Pins for the High Voltage Converters. The converters regulate the corre - sponding feedback pin to the lesser of 1V or the voltage on the associated TRKSS pin. FB3 (Pin 24): Feedback Input Pin for the Low Voltage Converter . The converter regulates the corresponding feedback pin to 800mV. Ground. These pins must be soldered to PCB ground. The exposed pad must also be soldered to PCB ground. INTV CC (Pin 28): Internal Regulator Bypass. Do not load the INTVCC pin with external circuitry. INTV CC is 3.1V when BIAS < 3.1V, 3.4V when BIAS > 3.4V, and approxi- mately equal to BIAS when BIAS is between 3.1V and 3.4V. Decouple to ground with a low ESR, 4.7μF capacitor . PG1, PG2 (Pins 1, 11): Power Good Indicators for Channels 1 and 2. Open-drain logic output pulls down until the corre- sponding FB pin rises above 0.92V but remains below 1.08V. PG3 (Pin 12): Power Good Indicator for Channel 3. Open- drain logic output pulls down until the corresponding FB pin rises above 0.736V but remains below 0.864V. POREN (Pin 39): Power-On Reset Enable. This is a logic input that starts the ramp on the POR timing capacitor . PVIN1, PVIN2 (Pins 37, 14): Input Supply Voltage to High Voltage Channels 1 and 2, respectively. These pins are independent and can be powered from different sources if necessary. Bypass each input with a low ESR capacitor to the adjacent GND pin. PVIN3 (Pin 17): Input Supply Voltage to Low Voltage Channel 3. This pin is typically connected to one of the high voltage converter outputs and should be locally bypassed with a low ESR capacitor . RST (Pin 32): Power-On Reset Output. CMOS output with weak pull-up, this pin is held low until the POR times out. RT (Pin 29): Frequency Programming Resistor . Connect a resistor from this pin to ground to set the internal oscil- lator frequency. RUN3 (Pin 18): Run Input for the Low Voltage Converter . Channel 3 is enabled when the voltage on this pin exceeds 0.72V (typical). SW1 (Pin 3): Channel 1 Switch Node. This is the output of the internal power switches for channel 1. SW2 (Pins 6, 7): Channel 2 Switch Node. This is the out- put of the internal power switches for channel 2. These pins must be connected together. SW3 (Pin 15) : Channel 3 Switch Node. This is the output of the internal power switches for channel 3. SYNC (Pin 33): Clock Synchronization and Mode Select Input. Connect this pin to ground to enable low ripple Burst Mode operation. Connect this pin to INTV CC to enable pulse skip operation. Apply a digital clock input to synchronize the LT8601 switching frequency to a refer - ence clock. When an external clock is applied, the LT8601 will operate in pulse-skipping mode. TRKSS1, TRKSS2 (Pins 21, 20): T rack/Soft-Start Inputs for the High Voltage Converters. When this pin is below 1V, the converter regulates the FB pin to the TRKSS volt- age instead of the internal reference. The TRKSS pin has a 2.4μA (typical) pull-up current. V IN (Pin 23): Input Supply Voltage to Internal Functions. This pin is independent from any PV IN pin and can be powered from different sources if necessary. V IN must be above 3V for the part to operate.

8601faFor more information www.linear .com/L T8601 block DiagraM 8601 BD 2.4µA FB2 ILIM2 ERROR AMPLIFIER BST1 BST2 LOOP COMPENSATION 1.08V 0.92V TRKSS2 PG2 SYNC RT GND RUN3 SW2 PVIN2 ILIM2 ILIM3 ILIM1 LOGIC CLK2 CLK2 CLK1 GND DRIVER DRIVER DRIVER CURRENT SENSE COMPARATOR CURRENT SENSE COMPARATOR REVERSE CURRENT COMPARATOR CURRENT SENSE COMPARATOR REVERSE CURRENT COMPARATOR REVERSE CURRENT COMPARATOR 0.8V INTVCC CLK2CLK1 SS3 2.4µA SS3 0.8V FB1 SW3 PVIN3 TRKSS1 PG1 GND SW1 PVIN1 GND FB3 ILIM1 ILIM3 ERROR AMPLIFIER ERROR AMPLIFIER 1.08V 0.92V 0.86V 0.74V PG3 CPOR BIAS LOOP COMPENSATION LOOP COMPENSATION OSCILLATOR INTVCC VIN REGULATOR RST POREN POWER-ON RESET EN/UVLO ENABLE REFERENCE LOGIC LOGIC

8601fa For more information www.linear .com/L T8601 operaTion The LT8601 is a triple channel, constant frequency, cur- rent mode, monolithic buck switching regulator with power-on reset. All channels are synchronized to a single oscillator . T wo of the channels are high voltage capable (up to 42V input) while the other is low voltage capable (up to 5.5V input) and is typically powered from the high voltage buck outputs. Start-Up When enabled by setting the EN/UVLO voltage above its threshold, the LT8601 starts charging the INTVCC capaci- tor from VIN. If BIAS is higher than 3.2V, BIAS supplies current to the INTV CC regulator to reduce V IN quiescent current. High Voltage Buck Regulators Each high voltage channel is a synchronous buck regu - lator that operates from an independent PV IN pin. The internal top power MOSFET is turned on at the beginning of each oscillator cycle, and turned off when the current flowing through the top MOSFET reaches a level deter - mined by the error amplifier . The error amplifier measures the output voltage through an external resistor divider tied to the FB pin to control the peak current in the top switch. The reference of the error amplifier is determined by the lower of the internal 1V reference and the voltage at its TRKSS pin. While the top MOSFET is off, the bottom MOSFET is turned on for the remainder of the oscillator cycle or until the inductor current starts to reverse. If overload condi - tions result in more than 2A for channel 1 or 3.3A for channel 2 flowing through the bottom switch, the next clock cycle will be delayed until switch current returns to a safe level. Low Voltage Buck Regulator The low voltage channel is a synchronous buck regulator that operates from an independent PVIN pin. The PVIN pin has an undervoltage lockout set at 2.35V (typical). Each internal top power MOSFET is turned on at the beginning of each oscillator cycle, and turned off when the current flowing through the top MOSFET reaches a level deter - mined by the error amplifier . The error amplifier measures the output voltage through an external resistor divider tied to the FB pin to control the peak current in the top switch. The reference of the error amplifier is an internal 800mV reference. The low voltage channel has a RUN pin to allow power sequencing and an internal soft-start circuit ramps the output voltage up in 1ms. While the top MOSFET is off, the bottom MOSFET is turned on for the remainder of the oscillator cycle or until the inductor current starts to reverse. If overload condi - tions result in more than 2.4A flowing through the bottom switch, the next clock cycle will be delayed until switch current returns to a safe level. Multiphase Switching The oscillator generates two clock signals 180° out of phase. Channel 1 operates from CLK1, while channels 2 and 3 operate from CLK2. Since a buck regulator only draws input current during the top switch on-cycle, mul- tiphase operation reduces peak input current and doubles the input current frequency. These effects reduce input current ripple and reduce the input capacitance required. Light Load Operation At light load, the regulators operate in low ripple Burst Mode operation. Low ripple Burst Mode operation shuts down most internal circuitry between switch on-cycles to conserve power while still retaining low ripple at the output. Undervoltage Lockout The EN/UVLO pin is used to put the LT8601 in shutdown, reducing the input current to less than 1μA. The accurate 1.2V (rising) threshold of the EN/UVLO pin provides a pro- grammable VIN undervoltage lockout through an external resistor divider tied to the EN/UVLO pin. A 50mV (typical) hysteresis voltage on the EN/UVLO pin prevents switch- ing noise from inadvertently shutting down the LT8601. Power Good Comparators Each channel has a power good comparator that trips when the feedback pin is above or below its reference voltage by more than 8%. The PG output pins are open- drain. The PG pin for each channel is pulled low when the corresponding output is out of regulation. The PG outputs are not valid until INTVCC rises to 2.7V

POREN pin is higher than 1.2V (typical). is enabled and INTVCC is above 2.7V. channel. R2 should be 200k or less to avoid noise problems. tor Cff may also be used. Typical values are 10pF to 100pF. noise sources, such as an inductor or a SW line. resistor value of RT for common switching frequencies. Table 1. Switching Frequency vs RT Value where RT is in kΩ and fS is in MHz. quency operation is higher efficiency. range increases when switching frequency decreases. table and Typical Performance curves section. Figure 1. Feedback Resistor Divider

8601 F01

1.2V PVIN Voltage Range Each switching regulator channel operates from its own PVIN pin (PVIN1 to PVIN3). The PVIN pin can be connected to either an independent voltage supply or a high voltage channel output. The PVIN1 and PVIN2 voltage range is 3.0V to 42V. The PVIN3 voltage range is 2.6V to 5.5V. The minimum PVIN voltage to regulate output voltage at full frequency is: PVINx(MIN) = VOUTx DCMAX where DC MAX is the maximum duty cycle (refer to Switching Frequency section) for that channel. If PV IN is below the calculated minimum voltage, the channel starts to skip switch off-cycles. At low input voltages, the part will turn on the top switch for longer than a full switch cycle in order to extend the effective duty cycle. When the part is extending the effective duty cycle, the switching frequency will drop to one half (or less) of the programmed frequency. The maximum PV IN voltage to regulate output voltage at full frequency is: PVINx(MAX) = VOUTx DCMIN where DC MIN is the minimum duty cycle (refer to Switching Frequency section) for that channel. If PV IN is above the calculated maximum voltage, the channel starts to skip switch on-cycles (pulse-skipping). In this case, the channel switching frequency will no longer be the programmed frequency. The output will continue to regulate, but the peak inductor current and output ripple will increase significantly. Inductor Selection Inductor selection involves inductance, saturation current, series resistance (DCR) and magnetic loss. A good starting point for the inductance values are: Lx =Kx •VOUTx PVINx
PVINx – VOUTx fS where fS is the switching frequency in MHz, Lx is in µH, VOUTx is the channel output voltage and K1 = 1.7, K2 = 1.0 and K3 = 1.4. Once the inductance is selected, the inductor current ripple and peak current can be calculated: ΔILx = VOUTx Lx •fS
1– VOUTx PVINx(MAX) ILx(PEAK) =IOUTx(MAX) + ΔILx To guarantee sufficient output current, peak inductor cur- rent must be lower than the switch current limit (ILIM). To keep the efficiency high, the inductor series resistance (DCR) should be as small as possible (must be < 0.1Ω channels 1 and 3; < 0.06 Ω channel 2), and the core mate- rial should be intended for the chosen switching frequency. Table 2 lists several vendors and suitable inductor series.

Table 2. Inductor Vendors

8601faFor more information www.linear .com/L T8601 applicaTions inForMaTion Of course, such a simple design guide will not always result in the optimum inductors for the applications. A larger value inductor provides a slightly higher maximum load current and will reduce the output voltage ripple. A larger value inductor can result in higher efficiency if the DCR and magnetic losses are the same. However , for inductors of the same dimensions, the larger value induc- tor has higher DCR. The trade-off between inductance and DCR is not always obvious. Use experiments to find optimum inductors. Low inductance may result in discontinuous mode oper- ation, which is acceptable, but reduces maximum load current. For details of maximum output current and dis- continuous mode operation, see the Linear Technology Application Note 44. For duty cycles greater than 50%, there is a minimum inductance required to avoid subhar- monic oscillations. LMINx = 1.05• VOUTx + VBOTx( ) fS , chs 1 and 3 LMINx = 0.70 • VOUTx + VBOTx( ) fS , ch 2 where VOUTx is the output voltage; V BOTx is the voltage across the bottom switch; f S is the switching frequency in MHz and L MINx is in µH. If the frequency is synchro - nized over a range, use the lowest frequency to determine LMINx. Shorted Output Protection If the bottom MOSFET current exceeds the valley current limit at the start of a clock cycle, the top MOSFET is kept off until the overcurrent situation clears. This prevents the buildup of inductor current during a shorted out - put. Further , during overload or short-circuit conditions, the LT8601 safely tolerates operation with a saturated inductor . Input Capacitor Selection Bypass each PVIN pin of the LT8601 with a ceramic capac- itor of X7R or X5R type. Step-down converters 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 LT8601 input and to force this switching current into a tight local loop, minimizing EMI. The input capaci- tor must have low impedance at the switching frequency to do this effectively and it must have an adequate ripple current rating. The worst case ripple current is when VOUT is one half of PVIN. In this case, the ripple current is: ICIN(RMS) = IOUT A reasonable value for the input capacitor is: 4.7µF fS , Chs 1 and 3 10µF fS , Ch 2 where fS is the switching frequency in MHz. Careful placement of C IN is essential to get the lowest ripple and EMI. CIN should be placed as close to the PVIN pin as possible and on the same side of the PC board. The layer immediately below the component traces should be an unbroken ground plane. The ground side of CIN should have at least 2 vias to the ground plane as close to C IN as possible. This provides a high frequency return path directly under the PVIN to CIN trace. This minimizes loop area of the high frequency, high current path from PV IN to CIN and back to the GND exposed pad. See Figure 8, Recommended PCB Layout. A word of caution is in order regarding the use of ceramic capacitors at the input. A ceramic input capacitor can combine with stray inductance to form a resonant tank circuit back to the supply. If power is applied quickly (for example by plugging the circuit into a live power source), this tank can ring, as much as doubling the input volt- age. The solution is to either clamp the input voltage or dampen the tank circuit by adding a lossy capacitor in parallel with the ceramic capacitor . For details, see Linear Technology Application Note 88.

the presence of output capacitor series resistance (ESR). and small circuit size, are therefore an option. VRIPPLE = ∆IL • ESR, for aluminum or tantalum. in µF and ESR is the output capacitor series resistance. tance with applied voltage and at temperature extremes. Table 3. Low ESR Capacitor Vendors cycles. In most cases, a 0.1μF capacitor will work well.

nel. The low voltage channel soft-start is set to 1ms. the capacitance on the TRKSS pin in F . the programmable EN/UVLO pin. RTR2 common node to the TRKSS pin of slave regulator. Figure 2. Example T racking Output Waveforms

8601 F02

Figure 5. Burst Mode Operation SW Waveforms with All Figure 3. In this case, both OUT1 and OUT3 are held high they are connected to external supplies. Figure 3. Reverse Protection Diodes Figure 4. Burst Mode Operation SW Waveforms with Oscillator

8601 F03

8601 F04

8601 F05

switching frequencies when in Burst Mode operation.

Figure 6. Power-On Reset Timing RT should be selected for 500kHz. Do not leave the SYNC pin floating. nels, and 736mV to 864mV for the low voltage channel. internal pull-up resistor to approximately 2V. Figure 7. Sequencing the Outputs and POR

8601 F07

8601 F06

voltage reaches the RUN threshold. undervoltage threshold, normal operation is active. within the circuit board and on the bottom side. Figure 8. Recommended PCB Layout

8601 F08

stop switching if the internal temperature rises too high. temperature and is intended as a failsafe only. range of frequencies and input voltages. Figure 9. Thermal Derating, E- and I-Grade Figure 10. Thermal Derating, E and I–Grade

8601 F09

8601fa For more information www.linear .com/L T8601 Typical applicaTions Details of Front Page Application Start-Up Sequence

8601 TA02a

5V , 1.5AC1 22µF C12 4.7µF 453k 3.3µH 113k GND SW1 EN/UVLO VIN VIN 6V TO 24V TRANSIENTS TO 42V BST1 L T8601 RST FB1 0.1µF PVIN1 C11 10µF PV IN2 OUT2 3.3V , 1A THE MAX CURRENT ON OUT2 IS I(OUT2) = 2.5A – IPVIN3 – IBIAS 47µF 316k 1.0µH 137k SW2 BST2 FB2 0.1µF INTVCCRT THE VALUES SHOWN ARE FOR 2MHz OPERATION. FOR 1MHz OPERATION, MAKE THE FOLLOWING CHANGES: AT 1MHz OPERATION, THE INPUT VOL TAGE RANGE IS 6V TO 42V . 4.7µF CFF1 10pF CFF2 22pF OUT3 1.8V , 1.8AC3 22µF 249k 200k 1.0µH SW3 FB3 PVIN3 BIAS 4.7µF TRKSS1 C13 2200pF TRKSS2 RUN3 PG1 OUT2 PG2 PG3 SYNC POREN CPOR CFF3 10pF R10 20k 28.7k Start–Up Sequence 200µs/DIV V OUT1 5V/DIV V OUT2 5V/DIV V OUT3 2V/DIV

8601 TA02b

8601faFor more information www.linear .com/L T8601 Automotive Input Steps Down to 5V, 3.3V, 1.8V

8601 TA03a

5V , 1.5AC1 22µF C12 4.7µF R12 499k 453k 4.7µH 113k GND SW1 EN/UVLOUVLO = 5.4V VIN VIN 6V TO 30V TRANSIENTS TO 42V BST1 L T8601 RST FB1 0.1µF PVIN1 UP_START C11 10µFR11 1.75M PV IN2 OUT2 3.3V , 1A THE MAX CURRENT ON OUT2 IS I (OUT2) = 2.5A – IPVIN3 – IBIAS 47µF 316k 2.2µH 137k SW2 BST2 FB2 0.1µF INTVCCRT SWITCHING FREQUENCY = 1.25MHz 4.7µF OUT3 1.8V , 1.8AC3 22µF 249k 200k 1.5µH SW3 FB3 C10 220pF PVIN3 BIAS 4.7µF TRKSS1 C13 2700pF TRKSS2 RUN3 PG1 OUT2 SYNC INPUT PG2 PG3 POREN SYNC CPOR R10 20k OUT2 20k 47.5k CFF1 4.7pF CFF2 22pF CFF3 22pF 1ms/DIV VOUT1 5V/DIV VOUT2 2V/DIV VOUT3 2V/DIV RST 2V/DIV

8601 TA03b

START-UP SEQUENCE: CH1 AND CH2 SOFT-START RATIOMETRICALL Y; THEN CH3 TURNS ON; THEN POR TIMER STARTS. Start-Up Sequence Typical applicaTions

8601fa For more information www.linear .com/L T8601 package DescripTion Please refer to http://www.linear .com/product/LT8601#packaging for the most recent package drawings. 6.00 ±0.10 (4 SIDES) NOTE: 1. DRAWING IS A JEDEC PACKAGE OUTLINE VARIATION OF (WJJD-2) 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 0.20mm ON ANY SIDE, IF PRESENT 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 PIN 1 TOP MARK (SEE NOTE 6) PIN 1 NOTCH R = 0.45 OR 0.35 × 45° CHAMFER 0.40 ±0.10 40 39 BOTTOM VIEW—EXPOSED PAD

4.50 REF

(4-SIDES) 4.42 ±0.10 4.42 ±0.10 4.42 ±0.05 4.42 ±0.05 0.75 ±0.05 R = 0.115 TYP 0.25 ±0.05

0.50 BSC

0.200 REF

0.00 – 0.05 (UJ40) QFN REV Ø 0406 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 0.70 ±0.05 4.50 ±0.05 (4 SIDES) 5.10 ±0.05 6.50 ±0.05 0.25 ±0.05 R = 0.10 TYP 40-Lead Plastic QFN (6mm × 6mm) (Reference LTC DWG # 05-08-1728 Rev Ø)

8601faFor more information www.linear .com/L T8601 Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However , no responsibility is assumed for its use. Linear Technology Corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

revision hisTory

REV DATE DESCRIPTION PAGE NUMBER A 06/17 Clarified Resitor Value for 2MHz Switching. Clarified Channels 1, 2, 3 Feedback Voltage Limits. Clarified RUN3 Threshold Upper Limits. Clarified RST Pull-Up Current. Clarified R T Value on Bottom Graphs. Clarified Conditions for EMI Performance Graphs. Clarified INTV CC (Pin 28) Description. Clarified BST and SW Pin Considerations Paragraph. Clarified Mode Selection and Synchronization Paragraph. Clarified Values in Power-On Reset Timer Paragraph. Clarified Sequencing Paragraph. 3, 4

8601fa For more information www.linear .com/L T8601  LINEAR TECHNOLOGY CORPORATION 2016 LT 0617 REV A • PRINTED IN USA www.linear.com/LT8601 PART NUMBER DESCRIPTION COMMENTS Synchronous Micropower Step-Down DC/DC Converter with IQ = 25µA VIN = 3V to 42V, VOUT(MIN)= 0.8V, IQ = 25µA, ISD < 1µA, 6mm × 6mm QFN-40 Package LT3507/LT3507A 36V, 2.7A + 1.8A + 1.8A + LDO Controller , 2.5MHz, High Efficiency, T riple Output Step-Down DC/DC Converter V IN = 4V to 36V, VOUT(MIN) = 0.8V, IQ = 7mA, ISD < 1µA, 5mm × 7mm QFN LT8640 42V, 6A, 96% Efficiency , 2.2MHz Synchronous Micropower Step-Down DC/DC Converter with IQ = 2.5µA VIN = 3.4V to 42V, VOUT(MIN) = 0.985V, IQ = 2.5µA, ISD < 1µA, 3mm × 4mm QFN 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) = 0.985V, IQ = 2.5µA, ISD < 1µA, 3mm × 4mm QFN 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) = 0.985V, IQ = 2.5µA, ISD < 1µA, 3mm × 6mm QFN LT8610/LT8610A/ LT8610AB/LT8610AC 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) = 0.985V, IQ = 2.5µA, ISD < 1µA, MSOP-16E 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) = 0.985V , IQ = 2.5µA, ISD < 1µA, 3mm × 5mm QFN-24 relaTeD parTs Typical applicaTion Wide Range Input Stepped Down to 5V, 2.5V and 8V (Delayed) Start-Up Sequence

8601 TA04

8V , 1.5AC1 47µF C12 4.7µF R12 287k 1000k 4.7µH 143k GND SW1 EN/UVLO UVLO = 9.6V VIN VIN 10V TO 24V TRANSIENTS TO 42V BST1 L T8601 RST FB1 0.1µF PVIN1 C11 10µFR11 PV IN2 OUT2 5V , 1A THE MAX CURRENT ON OUT2 IS I (OUT2) = 2.5A – IPVIN3 – IBIAS 47µF 549k 2.2µH 137k SW2 BST2 FB2 0.1µF INTVCCRT SWITCHING FREQUENCY = 2.2MHz 4.7µF OUT3 2.5V , 1.8AC3 47µF 243k 115k 1µH SW3 FB3 C10 330pF PVIN3 BIAS 4.7µF TRKSS1 C13 2700pF C14 1000pF TRKSS2 RUN3 PG1 OUT2 PG2 PG3 SYNC POREN CPOR R10 20k 20k 26.1k CFF3 10pF CFF2 10pF CFF1 10pF INTVCC 2ms/DIV VOUT1 5V/DIV VOUT2 5V/DIV VOUT3 2V/DIV RST 2V/DIV

8601 TA04b

START-UP SEQUENCE: CH2 SOFT-STARTS; THEN CH3 TURNS ON; THEN POR TIMER STARTS; AFTER POR TIMES OUT , THEN CH1 STARTS.

Product Information

LT8601 specifications and overview.

Summary

42V Triple Monolithic Synchronous Step-Down Regulator

Description

42V Triple Monolithic Synchronous Step-Down Regulator

Source title LT8601 Datasheet(PDF) - Linear Technology

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