LT3755

LT3791EFE-1 LINER

Document overview

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Technical content

37911faFor more information www.linear .com/L T3791-1 Typical applicaTion FeaTures DescripTion 60V 4-Switch Synchronous Buck-Boost Controller The LT®3791-1 is a synchronous 4-switch buck-boost volt- age/current regulator controller. The controller can regulate output voltage, output current, or input current with input voltages above, below, or equal to the output voltage. The constant-frequency, current mode architecture allows its frequency to be adjusted or synchronized from 200kHz to 700kHz. No top FET refresh switching cycle is needed in buck or boost operation. With 60V input, 60V output capability and seamless transitions between operating regions, the LT3791-1 is ideal for voltage regulator, bat- tery/super-capacitor charger applications in automotive, industrial, telecom, and even battery-powered systems. The LT3791-1 provides input current monitor, output current monitor, and various status flags, such as C/10 charge termination and shorted output flag. L, LT, LT C, LT M, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. 120W (24V 5A) Buck-Boost Voltage Regulator

applicaTions

n 4-Switch Single Inductor Architecture Allows VIN Above, Below or Equal to VOUT n Synchronous Switching: Up to 98.5% Efficiency n Wide VIN Range: 4.7V to 60V n 2% Output Voltage Accuracy: 1.2V ≤ VOUT < 60V n 6% Output Current Accuracy: 0V ≤ VOUT < 60V n Input and Output Current Regulation with Current Monitor Outputs n No Top FET Refresh in Buck or Boost n VOUT Disconnected from VIN During Shutdown n C/10 Charge Termination and Output Shorted Flags n Capable of 100W or greater per IC n 38-Lead TSSOP with Exposed Pad Efficiency vs Load Current n Automotive, T elecom, Industrial Systems n High Power Battery-Powered System LOAD CURRENT (A) 0 1 EFFICIENCY (%) 100

37911 TA01b

VIN = 12V VIN = 24V VIN = 54V VIN 12V TO 58V INTVCC TG1 BG1 SNSP SNSN BST1 BST2 BG2 PGND SW2 TG2 RT L T3791-1 SWI SHORT C/10 CCM 470nF IVINN VIN IVINP IVINMON ISMON CLKOUT PWMOUT TEST1 EN/UVLO OVLO VREF PWM CTRL 147k 200kHz VCSYNC SS SGND 1µF 499k 56.2k 100k 499k 27.4k INTVCC 0.1µF 33nF 10nF

37911 TA01a

0.004/uni03A9 ISP ISN FB 0.1µF 10µH 0.1µF 4.7µF 4.7µF 50V 4.7µF 100V 47µF 80V 0.015/uni03A9 V OUT 24V 73.2k 3.83k 5.1k 220µF 35V 100k 200k 0.003/uni03A9 50/uni03A9

37911fa For more information www.linear .com/L T3791-1 pin conFiguraTionabsoluTe MaxiMuM raTings Supply Voltages SW1, to 60V EN/U IN V IV 0.5V 0.3V Operating Junction Temperature (Notes 2, 3) LT379 65°C to 150°C 0°C (Note 1) TOP VIEW FE PACKAGE 38-LEAD PLASTIC TSSOP CTRL SS PWM C/10 SHORT V REF ISMON IVINMON EN/UVLO IVINP IVINN VIN INTVCC TG1 BST1 SW1 PGND BG1 BG2 OVLO FB V C RT SYNC CLKOUT CCM PWMOUT SGND TEST1 SNSN SNSP ISN ISP TG2 NC BST2 SW2 PGND SGND TJMAX = 150°C, θJA = 28°C/W EXPOSED PAD (PIN 39) IS SGND, MUST BE SOLDERED TO PCB elecTrical characTerisTics The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = 12V, VEN/UVLO = 12V unless otherwise noted. orDer inForMaTion LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3791EFE-1#PBF LT3791EFE-1#TRPBF LT3791FE-1 38-Lead Plastic TSSOP –40°C to 125°C LT3791IFE-1#PBF LT3791IFE-1#TRPBF LT3791FE-1 38-Lead Plastic TSSOP –40°C to 125°C LT3791HFE-1#PBF LT3791HFE-1#TRPBF LT3791FE-1 38-Lead Plastic TSSOP –40°C to 150°C LT3791MPFE-1#PBF LT3791MPFE-1#TRPBF LT3791FE-1 38-Lead Plastic TSSOP –55°C to 150°C Consult LT C 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/ PARAMETER CONDITIONS MIN TYP MAX UNITS Input VIN Operating Voltage 4.7 60 V VIN Shutdown IQ VEN/UVLO = 0V 0.1 1 µA VIN Operating IQ (Not Switching) FB = 1.3V , RT = 59.0k 3.0 4 mA

37911faFor more information www.linear .com/L T3791-1 elecTrical characTerisTics The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = 12V, VEN/UVLO = 12V unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Logic Inputs EN/UVLO Falling Threshold l 1.16 1.2 1.24 V EN/UVLO Rising Hysteresis 15 mV EN/UVLO Input Low Voltage IVIN Drops Below 1µA 0.3 V EN/UVLO Pin Bias Current Low VEN/UVLO = 1V 2 3 4 µA EN/UVLO Pin Bias Current High VEN/UVLO = 1.6V 10 100 nA CCM Threshold Voltage 0.3 1.5 V CTRL Input Bias Current VCTRL = 1V 20 50 nA CTRL Latch-Off Threshold 175 mV OVLO Rising Shutdown Voltage l 2.85 3 3.15 V OVLO Falling Hysteresis 75 mV Regulation V REF Voltage l 1.96 2.00 2.04 V VREF Line Regulation 4.7V < VIN < 60V 0.002 0.04 %/V V(ISP-ISN) Threshold VCTRL = 2V l 97.5 100 100 102.5 106 mV mV VCTRL = 1100mV l mV mV V CTRL = 700mV l 47.5 52.5 mV mV V CTRL = 300mV l 6.5 13.5 mV mV ISP Bias Current 110 µA ISN Bias Current 20 µA Output Current Sense Common Mode Range 0 60 V Output Current Sense Amplifier g m 890 µS ISMON Monitor Voltage V(ISP-ISN) = 100mV l 0.96 1 1.04 V Input Current Sense Threshold V(IVINP-IVINN) 3V ≤ VIVINP ≤ 60V l 46.5 50 54 mV IVINP Bias Current 90 µA IVINN Bias Current 20 µA Input Current Sense Common Mode Range 3 60 V Input Current Sense Amplifier gm 2.12 mS IVINMON Monitor Voltage V(IVINP-IVINN) = 50mV l 0.96 1 1.04 V FB Regulation Voltage l 1.194 1.176 1.2 1.2 1.206 1.220 V V FB Line Regulation 4.7V < V IN < 60V 0.002 0.025 %/V FB Amplifier gm 565 µS FB Pin Input Bias Current FB in Regulation 100 150 nA VC Standby Input Bias Current PWM = 0V –20 20 nA VSENSE(MAX) (VSNSP-SNSN) Boost Buck l l –56 –47.5 –39 mV mV Fault SS Pull-Up Current VSS = 0V 14 µA SS Discharge Current 1.4 µA

37911fa For more information www.linear .com/L T3791-1 elecTrical characTerisTics The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = 12V, VEN/UVLO = 12V unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS C/10 Rising Threshold (VFB) V(ISP-ISN) = 0V l 1.127 1.15 1.173 V C/10 Falling Threshold (VFB) l 1.078 1.1 1.122 V C/10 Falling Threshold (V(ISP-ISN)) VFB = 1.2V 5 10 15 mV SHORT Falling Threshold (VFB) 380 400 450 mV C/10 Pin Output Impedance 1.1 2.0 kΩ SHORT Pin Output Impedance 1.1 2.0 kΩ SS Latch-Off Threshold 1.75 V SS Reset Threshold 0.2 V Oscillator Switching Frequency RT = 147k RT = 59.0k RT = 29.1k 190 380 665 200 400 700 210 420 735 kHz kHz kHz SYNC Frequency 200 700 kHz SYNC Pin Resistance to GND 90 kΩ SYNC Threshold Voltage 0.3 1.5 V Internal VCC Regulator INTVCC Regulation Voltage 4.8 5 5.2 V Dropout (VIN – INTVCC) IINTVCC = –10mA, VIN = 5V 240 350 mV INTVCC Undervoltage Lockout 3.1 3.5 3.9 V INTVCC Current Limit VINTVCC = 4V 67 mA PWM PWM Threshold Voltage 0.3 1.5 V PWM Pin Resistance to GND 90 kΩ PWMOUT Pull-Up Resistance 10 20 Ω PWMOUT Pull-Down Resistance 5 10 Ω NMOS Drivers TG1, TG2 Gate Driver On-Resistance Gate Pull-Up Gate Pull-Down V BST – VSW = 5V 2.6 1.7 Ω Ω BG1, BG2 Gate Driver On-Resistance Gate Pull-Up Gate Pull-Down V INTVCC = 5V 1.2 Ω Ω TG Off to BG On Delay C L = 3300pF 60 ns BG Off to TG On Delay CL = 3300pF 60 ns TG1, TG2, tOFF(MIN) RT = 59.0k 240 300 ns 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 LT3791E-1 is guaranteed to meet performance from 0°C to 125°C junction temperature. Specification over the -40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LT3791I-1 is guaranteed to meet performance specifications over the –40°C to 125°C operating junction temperature range. The LT3791H-1 is guaranteed to meet performance specifications over the –40°C to 150°C operating junction temperature range. The LT3791MP-1 is guaranteed to meet performance specifications over the –55°C to 150°C operating junction temperature range. High junction temperatures degrade operating lifetimes. Operating lifetime is derated for junction temperatures greater than 125°C. Note 3: The LT3791-1 includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed the maximum operating junction temperature when overtemperature protection is active. Continuous operation above the specified absolute maximum operating junction temperature may impair device reliability.

37911faFor more information www.linear .com/L T3791-1 Typical perForMance characTerisTics INTVCC Load Regulation VREF Voltage vs Temperature VREF Load Regulation INTVCC Dropout Voltage vs Current, Temperature INTVCC Voltage vs Temperature TA = 25°C, unless otherwise noted. INTVCC Current Limit vs Temperature LDO CURRENT (mA) VIN-VINTVCC (V) 1.0 1.5

37911 G01

0.5 10 20 30 2.5 2.0 TA = 150°C TA = 25°C TA = –50°C TEMPERATURE (°C) –50 INTVCC (V) 5.00 5.10 150

37911 G02

4.90 4.80 0 50 100–25 25 75 125 5.20 4.95 5.05 4.85 5.15 VIN = 60V VIN = 12V TEMPERATURE (°C) –50 INTVCC CURRENT LIMIT (mA) 0 50 75

37911 G03

–25 25 100 125 150 ILOAD (mA) INTVCC (V) 5.75

37911 G04

5.00 4.50 10 20 40 4.25 4.00 6.00 5.50 5.25 4.75 50 60 TEMPERATURE (°C) –50 VREF (V)2.00 2.02 150

37911 G05

1.98 1.96 0 50 100–25 25 75 125 2.04 1.99 2.01 1.97 2.03 VIN = 60V VIN = 12V VIN = 4.7V IREF (µA) VREF (V)2.00 2.10 400

37911 G06

1.90 1.80 100 200 30050 150 250 350 2.20 1.95 2.05 1.85 2.15 V(ISP-ISN) Threshold vs VCTRL V(ISP-ISN) Threshold vs VISP V(ISP-ISN) Threshold vs Temperature VCTRL (V) V(ISP-ISN) (mV) 100 110

37911 G07

VISP (V) V(ISP-ISN) (mV) 100 102 30 50

37911 G08

TEMPERATURE (°C) –50 V(ISP-ISN) (mV) 100 104 150

37911 G09

0 50 100–25 25 75 125

108 VIN = 12V

VISP = 60V VISP = 12V VISP = 0V

37911fa For more information www.linear .com/L T3791-1 V(ISP-ISN) Threshold vs VFB ISMON Voltage vs Temperature ISMON Voltage vs V(ISP-ISN) V(IVINP-IVINN) Threshold vs Temperature V(IVINP-IVINN) Threshold vs VFB V(IVINP-IVINN) Threshold vs VIVINP IVINMON Voltage vs Temperature FB Regulation Voltage vs Temperature SHORT Threshold vs Temperature VFB (V) 1.17 V(ISP-ISN) (mV) 120 1.18 1.19 1.20 1.21

37911 G10

1.22 1.23 100 TEMPERATURE (°C) –50 VISMON (V) 1.00 1.02 150

37911 G11

0.98 0.96 0 50 100–25 25 75 125 1.04 0.99 1.01 0.97 1.03 VIN = 12V V(ISP-ISN) = 100mV V(ISP-ISN) (mV) VISMON (V)0.6 0.8 1.0

37911 G12

0.4 0.2 0.5 0.7 0.9 0.3 0.1 20 10 40 30 60 70 9050 100 TEMPERATURE (°C) –50 V(IVINP-IVINN) (mV) 25 50 75 100 125

37911 G13

–25 0 150 VIVINP = 60V VIVINP = 3V VIVINP (V) V(IVINP-IVINN) (mV) 49.5 50.0 50.5 30 50

37911 G14

49.0 48.5 48.0 10 20 40 51.0 51.5 52.0 TEMPERATURE (°C) –50 VIVINMON (V) 1.00 1.02 150

37911 G15

0.98 0.96 0 50 100–25 25 75 125 1.04 0.99 1.01 0.97 1.03 VIVINP = 12V V(IVINP-VINN) = 50mV VFB (V) 1.17 V(IVINP-IVINSN) (mV) 1.18 1.19 1.20 1.21

37911 G16

1.22 1.23 TEMPERATURE (°C) –50 VFB (V)1.20 1.22 150

37911 G17

1.18 1.16 0 50 100–25 25 75 125 1.24 1.19 1.21 1.17 1.23 VIN = 60V VIN = 12V VIN = 4.7V TEMPERATURE (°C) –50 FB VOLTAGE (V) 0.400 0.450 150

37911 G18

0.350 0.300 0 50 100–25 25 75 125 0.500 0.375 0.425 0.325 0.475 RISING FALLING Typical perForMance characTerisTics TA = 25°C, unless otherwise noted.

37911faFor more information www.linear .com/L T3791-1 C/10 Threshold vs Temperature OVLO Threshold vs Temperature Soft-Start Current vs Temperature Supply Current vs Input Voltage EN/UVLO Pin Current EN/UVLO Threshold Voltage TEMPERATURE (°C) –50 FB VOLTAGE (V) 1.100 1.150 150

37911 G19

1.050 1.000 0 50 100–25 25 75 125 1.200 1.075 1.125 1.025 1.175 RISING FALLING TEMPERATURE (°C) –50 OVLO THRESHOLD (V) 2.9 3.1 150

37911 G20

2.7 2.5 0 50 100–25 25 75 125 3.3 2.8 3.0 2.6 3.2 RISING FALLING TEMPERATURE (°C) –50 ISS (µA)8 150

37911 G21

0 50 100–25 25 75 125

14 CHARGING

VIN (V) IQ (mA) 1.5 2.0 2.5 30 50

37911 G22

1.0 0.5 10 20 40 3.0 3.5 4.0 TA = 150°C TA = 25°C TA = –50°C TEMPERATURE (°C) –50 EN/UVLO PIN CURRENT (µA) 150

37911 G23

0 50 100–25 25 75 125 VEN/ULO = 1V TEMPERATURE (°C) –50

1.10 EN/UVLO THRESHOLD (V)

1.12 1.16 1.18 1.20 1.30 1.24 0 50 75

37911 G24

1.14 1.26 1.28 1.22 –25 25 100 125 150 RISING FALLING Oscillator Frequency vs Temperature TG1, TG2 Minimum On-Time vs Temperature TG1, TG2 Minimum Off-Time vs Temperature TEMPERATURE (°C) –50 SWITCHING FREQUENCY (kHz) 400 600 150

37911 G25

0 50 100–25 25 75 125 800 300 500 100 700 RT = 29.1k RT = 59.0k RT = 147k TEMPERATURE (°C) –50 TG1, TG2 MINIMUM ON-TIME (ns) 150

37911 G26

0 50 100–25 25 75 125 100 TG1 TG2 TEMPERATURE (°C) –50 TG1, TG2 MINIMUM OFF-TIME (ns) 200 250 300 100 125

37911 G27

–25 0 25 50 75 150 350 fSW = 200kHz fSW = 400kHz fSW = 700kHz Typical perForMance characTerisTics TA = 25°C, unless otherwise noted.

37911fa For more information www.linear .com/L T3791-1 V(BST1-SW1), V(BST2-SW2) UVLO vs Temperature BG1, BG2 Driver On-Resistance vs Temperature TG1, TG2 Driver On-Resistance vs Temperature PWMOUT On-Resistance vs Temperature V C Voltage vs Duty Cycle V(SNSP-SNSN) Buck Threshold vs VC V(SNSP-SNSN) Buck Threshold vs Temperature V(SNSP-SNSN) Boost Threshold vs VC V(SNSP-SNSN) Boost Threshold vs Temperature TEMPERATURE (°C) –50 V(BST1-SW1), V(BST2,SW2) (V) 3.5 3.7 150

37911 G28

3.3 3.1 0 50 100–25 25 75 125 3.9 3.4 3.6 3.2 3.8 RISING FALLING TEMPERATURE (°C) –50 BG1, BG2 RESISTANCE (/uni03A9) 2.5 3.0 3.5 150

37911 G29

2.0 1.5 0 50 100–25 25 75 125 0.5 1.0 4.5 4.0 PULL-UP PULL-DOWN TEMPERATURE (°C) –50 TG1, TG2 RESISTANCE (/uni03A9) 2.0 3.0 150

37911 G30

1.0 0 50 100–25 25 75 125 4.0 1.5 2.5 0.5 3.5 PULL-UP PULL-DOWN TEMPERATURE (°C) –50 PWMOUT RESISTANCE (/uni03A9) 100 125

37911 G31

–25 0 25 50 75 150 PULL-UP PULL-DOWN DUTY CYCLE (%) VC (V) 0.6 0.8 1.0 60 100

37911 G32

0.4 0.2 20 40 80 1.2 1.4 1.6 BG2 BG1 V(SNSP-SNSN) = 0V VC (V) 0.6 –60 V(SNSP-SNSN) (mV) –40 –20 0.8 1.0 1.2 1.4

37911 G33

1.6 1.8 TEMPERATURE (°C) –50 –60 V(SNSP-SNSN) THRESHOLD (mV) –40 –20 0 50 100 150

37911 G34

–25 25 75 125 VC(MIN) VC(MAX) VC (V) 0.6 –20 –40 –60 –80 1.2 1.6

37911 G35

0.8 1.0 1.4 1.8 V(SNSP-SNSN) (mV) TEMPERATURE (°C) –50 V(SNSP-SNSN) THRESHOLD (mV) 100 125

37911 G36

–20 –40 –25 0 25 50 75 150 –60 –80 VC(MAX) VC(MIN) Typical perForMance characTerisTics TA = 25°C, unless otherwise noted.

37911faFor more information www.linear .com/L T3791-1 pin FuncTions CTRL (Pin 1): Output Current Sense Threshold Adjustment Pin. Regulating threshold V(ISP-ISN) is 1/10th of (VCTRL – 200mV). CTRL linear range is from 200mV to 1.1V . For VCTRL > 1.3V , the current sense threshold is constant at the full-scale value of 100mV . For 1.1V < VCTRL < 1.3V , the dependence of the current sense threshold upon VCTRL tran- sitions from a linear function to a constant value, reaching 98% of full scale by VCTRL = 1.2V . Connect CTRL to VREF for the 100mV default threshold. Force less than 175mV (typical) to stop switching. Do not leave this pin open. SS (Pin 2): Soft-start reduces the input power sources surge current by gradually increasing the controller’s cur- rent limit. A minimum value of 22nF is recommended on this pin. A 100k resistor must be placed between SS and VREF for the LT3791-1. PWM (Pin 3): A signal low turns off switches, idles switch- ing and disconnects the VC pin from all external loads. The PWMOUT pin follows the PWM pin. PWM has an internal 90k pull-down resistor . If not used, connect to INTVCC. C/10 (Pin 4): C/10 Charge Termination Pin. An open-drain pull-down on C/10 asserts if FB is greater than 1.15V (typi- cal) and V(ISP-ISN) is less than 10mV (typical). To function, the pin requires an external pull-up resistor . SHORT (Pin 5): Output Shorted Pin. An open-drain pull- down on SHORT asserts if FB is less than 400mV (typical). To function, the pin requires an external pull-up resistor . VREF (Pin 6): Voltage Reference Output Pin, Typically 2V . This pin drives a resistor divider for the CTRL pin, either for output current adjustment or for temperature limit/ compensation of the output load. Can supply up to 200µA of current. ISMON (Pin 7): Monitor pin that produces a voltage that is ten times the voltage V (ISP-ISN). ISMON will equal 1V when V(ISP-ISN) = 100mV . IVINMON (Pin 8): Monitor pin that produces a voltage that is twenty times the voltage V (IVINP-IVINN). IVINMON will equal 1V when V(IVINP-IVINN) = 50mV . EN/UVLO (Pin 9): Enable Control Pin. Forcing an accurate 1.2V falling threshold with an externally programmable hysteresis is generated by the external resistor divider and a 3µA pull-down current. Above the 1.2V (typical) threshold (but below 6V), EN/UVLO input bias current is sub-µA. Below the falling threshold, a 3µA pull-down cur- rent is enabled so the user can define the hysteresis with the external resistor selection. An undervoltage condition resets soft-start. Tie to 0.3V , or less, to disable the device and reduce VIN quiescent current below 1µA. IVINP (Pin 10): Positive Input for the Input Current Limit and Monitor . Input bias current for this pin is typically 90µA. IVINN (Pin 11): Negative Input for the Input Current Limit and Monitor . The input bias current for this pin is typically 20µA. VIN (Pin 12): Main Input Supply. Bypass this pin to PGND with a capacitor . INTV CC (Pin 13): Internal 5V Regulator Output. The driver and control circuits are powered from this voltage. Bypass this pin to PGND with a minimum 4.7µF ceramic capacitor . TG1 (Pin 14): Top Gate Drive. Drives the top N-channel MOSFET with a voltage equal to INTVCC superimposed on the switch node voltage SW1. BST1 (Pin 15): Bootstrapped Driver Supply. The BST1 pin swings from a diode voltage below INTV CC up to a diode voltage below VIN + INTVCC. SW1 (Pin 16): Switch Node. SW1 pin swings from a diode voltage drop below ground up to VIN. PGND (Pins 17, 20): Power Ground. Connect these pins closely to the source of the bottom N-channel MOSFET . BG1 (Pin 18): Bottom Gate Drive. Drives the gate of the bottom N-channel MOSFET between ground and INTVCC. BG2 (Pin 19): Bottom Gate Drive. Drives the gate of the bottom N-channel MOSFET between ground and INTVCC. SW2 (Pin 21): Switch Node. SW2 pin swings from a diode voltage drop below ground up to VOUT.

37911fa For more information www.linear .com/L T3791-1 pin FuncTions BST2 (Pin 22): Bootstrapped Driver Supply. The BST2 pin swings from a diode voltage below INTVCC up to a diode voltage below VOUT + INTVCC. NC (Pin 23): No Connect Pin. Leave this pin floating. TG2 (Pin 24): Top Gate Drive. Drives the top N-channel MOSFET with a voltage equal to INTVCC superimposed on the switch node voltage SW2. ISP (Pin 25): Connection Point for the Positive Terminal of the Output Current Feedback Resistor . ISN (Pin 26): Connection Point for the Negative Terminal of the Output Current Feedback Resistor . SNSP (Pin 27): The Positive Input to the Current Sense Comparator . The V C pin voltage and controlled offsets between the SNSP and SNSN pins, in conjunction with a resistor , set the current trip threshold. SNSN (Pin 28): The Negative Input to the Current Sense Comparator . TEST1 (Pin 29): This pin is used for testing purposes only and must be connected to SGND for the part to operate properly. SGND (Pin 30, Exposed Pad Pin 39): Signal Ground. All small-signal components and compensation should connect to this ground, which should be connected to PGND at a single point. Solder the exposed pad directly to the ground plane. PWMOUT (Pin 31): Buffered Version of PWM Signal for Driving Output Load Disconnect N-Channel MOSFET . The PWMOUT pin is driven from INTV CC. Use of a MOSFET with a gate cutoff voltage higher than 1V is recommended. CCM (Pin 32): Continuous Conduction Mode Pin. When the pin voltage is higher than 1.5V , the part runs in fixed frequency forced continuous conduction mode and al - lows the inductor current to flow negative. When the pin voltage is less than 0.3V , the part runs in discontinuous conduction mode and does not allow the inductor current to flow backward. This pin is only meant to block inductor reverse current, and should only be pulled low when the output current is low. This pin must be either connected to INTVCC (pin 13) for continuous conduction mode across all loads, or it must be connected to the C/10 (pin 4) with a pull-up resistor to INTV CC for continuous conduction mode at heavy load and for discontinuous conduction mode at light load. CLKOUT (Pin 33): Clock Output Pin. A 180° out-of-phase clock is provided at the oscillator frequency to allow for par- alleling two devices for extending output power capability. SYNC (Pin 34): External Synchronization Input Pin. This pin is internally terminated to GND with a 90k resistor . The internal buck clock is synchronized to the rising edge of the SYNC signal while the internal boost clock is 180° phase shifted. RT (Pin 35): Frequency Set Pin. Place a resistor to GND to set the internal frequency. The range of oscillation is 200kHz to 700kHz. V C (Pin 36): Current Control Threshold and Error Amplifier Compensation Point. The current comparator threshold increases with this control voltage. The voltage ranges from 0.7V to 1.9V . FB (Pin 37): Voltage Loop Feedback Pin. FB is intended for constant-voltage regulation. The internal transconductance amplifier with output V C will regulate FB to 1.2V (typical) through the DC/DC converter . If the FB input is regulat- ing the loop and V (ISP-ISN) < 10mV , the C/10 pull-down is asserted. If the FB pin is less than 400mV , the SHORT pull-down is asserted. OVLO (Pin 38): Overvoltage Input Pin. This pin is used for OVLO, if OVLO > 3V then SS is pulled low, the part stops switching and resets. Do not leave this pin open.

37911faFor more information www.linear .com/L T3791-1 block DiagraM 0.2V 1.15V 0.4V FB A18 1.75V 1.4µA VC OVLO 37911 BD SS PWMOUT PWM A17 INTVCC SGND 30, 39 C/10 A12 1.2V14µA 3µA SHDN_INT VREF A11 A10 A16 A15 ISMON_INT IVINMON_INT CTRL 1 FB 37 SNSN 28 SNSP 27 BST2 22 TG2 SW2 INTVCC INTVCC SHORT Q SS RESET SS LATCH R S A13 SW1 16 TG1 BST1 15 BG2 19 A14 BG1 PWM PGND 17 BUCK LOGIC SS LATCH SS_RESET SHDN_INT OSC SLOPE_COMP_BOOST SLOPE_COMP_BUCK 1.2V EN/UVLO9 IVINMON8 ISMON ISMON_INT ISP ISN RT35 CCM32 SYNC34 CLKOUT33 IVINMON_INT IVINP IVINN 10 11 VIN SHDN_INT VREF INTVCC BOOST LOGIC REGS A = 10 A = 10 A = 20 A = 24 TSD

output voltage above, equal to or below the input voltage. the current sense voltage is regulated to 50mV. level and regulate the output (constant-voltage mode). input and output current amplifiers respectively. typically improves peak efficiency by 1% to 2% at 500kHz. buck-boost region is reached.

37911 F01

37911 F02

Figure 1. Simplified Diagram of the Output Switches Figure 2. Operating Regions vs Duty Cycle

Figure 3. Buck Operation (VIN > VOUT)

37911 F03

Figure 4. Buck-Boost Operation (VIN ≤ VOUT) Figure 5. Buck-Boost Operation (VIN ≥ VOUT)

37911 F04

37911 F05

37911 F06

Figure 6. Boost Operation (VIN < VOUT)

can operate up to an input voltage of 60V. may not allow sufficiently high or low duty cycle operation. the RT pin to GND is required; do not leave this pin open. Table 1. Switching Frequency vs RT Value otherwise maintain the duty cycle between 10% and 90%. edge of CLKOUT turns on switch M2. noise, use a shielded inductor.

37911 F07

Figure 7. Maximum Peak-to-Peak Ripple vs Duty Cycle

37911fa For more information www.linear .com/L T3791-1 applicaTions inForMaTion current in boost operation and the maximum inductor valley current in buck operation. In boost operation, the maximum average load current at VIN(MIN) is: IOUT(MAX _BOOST) = 51 mV RSENSE – ΔIL ⎟ • VIN(MIN) VOUT where ΔIL is peak-to-peak inductor ripple current. In buck operation, the maximum average load current is: IOUT(MAX _BUCK) = 47.5mV RSENSE + ΔIL The maximum current sensing RSENSE value for the boost operation is: RSENSE(MAX) = 2 • 51 mV• VIN(MIN) 2 •ILED • VOUT + ΔIL(BOOST) • VIN(MIN) The maximum current sensing RSENSE value for the buck operation is: RSENSE(MAX) = 2 • 47.5mV 2 •ILED – ΔIL(BUCK) The final RSENSE value should be lower than the calculated RSENSE(MAX) in both the boost and buck operation. A 20% to 30% margin is usually recommended. CIN and COUT Selection In boost operation, input current is continuous. In buck operation, input current is discontinuous. In buck opera- tion, the selection of input capacitor, CIN, is driven by the need to filter the input square wave current. Use a low ESR capacitor sized to handle the maximum RMS current. For buck operation, the input RMS current is given by: IRMS = ILED2 •D+ ΔIL2 12 •D The formula has a maximum at V IN = 2V OUT. Note that ripple current ratings from capacitor manufacturers are often based on only 2000 hours of life which makes it advisable to derate the capacitor. In boost operation, the discontinuous current shifts from the input to the output, so C OUT must be capable of reducing the output voltage ripple. The effects of ESR (equivalent series resistance) and the bulk capacitance must be considered when choosing the right capacitor for a given output ripple voltage. The steady ripple due to charging and discharging the bulk capacitance is given by: ΔVRIPPLE BOOST _ CAP( ) = ILED • VOUT – VIN(MIN)( ) COUT • VOUT • f ΔVRIPPLE BUCK _ CAP( ) ≈ ΔIL 8 • f • COUT where COUT is the output filter capacitor. The steady ripple due to the voltage drop across the ESR is given by: Δ VBOOST(ESR) = ILED • ESR Δ VBUCK(ESR) = ILED • ESR Multiple capacitors placed in parallel may be needed to meet the ESR and RMS current handling requirements. Output capacitors are also used for stability for the LT3791 -1. A good starting point for output capacitors is seen in the Typical Applications circuits. Ceramic capacitors have excellent low ESR characteristics but can have a high voltage coefficient and are recommended for applications less than 100W. Capacitors available with low ESR and high ripple current ratings, such as OS-CON and POSCAP may be needed for applications greater than 100W. Programming V IN UVLO and OVLO The falling UVLO value can be accurately set by the resistor divider R1 and R2. A small 3µA pull-down current is active when the EN/UVLO is below the threshold. The purpose of this current is to allow the user to program the rising hysteresis. The following equations should be used to determine the resistor values: VIN(UVLO –) = 1.2 • R1+R2 VIN(UVLO+) = 3µA •R1+1.215 • R1+R2

Figure 8. Resistor Connection to Set VIN UVLO and

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Table 2. V(ISP-ISN) Threshold vs CTRL output power and switching current when V IN is low. care must be taken not to load this pin. LT3791-1 has a standalone current sense amplifier. vs VCTRL is listed in Table 2.

so care must be taken not to load this pin. pulse is synchronized to the SYNC signal. SHORT, which pulls low when the FB pin is below 400mV. 40% to 50% of the final value. the C/10 provides a C/10 charge termination flag. Figure 9. Resistor Connection for Constant Output

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37911faFor more information www.linear .com/L T3791-1 Soft-Start Soft-start reduces the input power sources’ surge currents by gradually increasing the controller’s current limit (pro- portional to an internally buffered clamped equivalent of VC). The soft-start interval is set by the soft-start capacitor selection according to the following equation tSS = 1.2V 14µA • CSS A 100k resistor must be placed between SS and VREF for the LT3791-1. This 100k resistor also contributes the extra SS charge current. Make sure CSS is large enough when there is loading during start-up. Loop Compensation The LT3791-1 uses an internal transconductance error amplifier whose VC output compensates the control loop. The external inductor, output capacitor and the compensa- tion resistor and capacitor determine the loop stability. The inductor and output capacitor are chosen based on performance, size and cost. The compensation resistor and capacitor at VC are set to optimize control loop response and stability. For typical applications, a 10nF compensation capacitor at VC is adequate, and a series resistor should always be used to increase the slew rate on the VC pin to maintain tighter regulation of output current during fast transients on the input supply of the converter. Power MOSFET Selections and Efficiency Considerations The LT3791-1 requires four external N- channel power MOSFETs, two for the top switches (switch M1 and M4, shown in Figure 1) and two for the bottom switches (switch M2 and M3 shown in Figure 1). Important parameters for the power MOSFETs are the breakdown voltage, VBR(DSS), threshold voltage, VGS(TH), on-resistance, RDS(ON), reverse transfer capacitance, CRSS, and maximum current, IDS(MAX). The drive voltage is set by the 5V INTV CC supply. Con- sequently, logic-level threshold MOSFETs must be used in LT3791-1 applications. If the input voltage is expected to drop below the 5V, then sub-logic threshold MOSFETs should be considered. In order to select the power MOSFETs, the power dis - sipated by the device must be known. For switch M1, the maximum power dissipation happens in boost operation, when it remains on all the time. Its maximum power dis- sipation at maximum output current is given by: PM1 (BOOST)= ILED • VOUT VIN

• ρT •RDS(ON) where ρT is a normalization factor ( unity at 25°C) accounting for the significant variation in on-resistance with temperature, typically 0.4%/°C as shown in Figure 10. For a maximum junction temperature of 125°C, using a value of ρT = 1.5 is reasonable. Switch M2 operates in buck operation as the synchronous rectifier. Its power dissipation at maximum output current is given by: PM2(BUCK) = VIN – VOUT VIN
• ILED2 • ρT •RDS(ON) Switch M3 operates in boost operation as the control switch. Its power dissipation at maximum current is given by: PM3(BOOST) = VOUT – VIN( ) • VOUT VIN2
• ILED2 • ρT •RDS(ON) + k • VOUT 3 • ILED VIN
• CRSS • f where CRSS is usually specified by the MOSFET manufac- turers. The constant k, which accounts for the loss caused by reverse-recovery current, is inversely proportional to the gate drive current and has an empirical value of 1.7. For switch M4, the maximum power dissipation happens in boost operation, when its duty cycle is higher than 50%. Its maximum power dissipation at maximum output current is given by: PM4(BOOST) = VIN VOUT
• ILED • VOUT VIN
• ρT •RDS(ON) For the same output voltage and current, switch M1 has the highest power dissipation and switch M2 has the low- est power dissipation unless a short occurs at the output. applicaTions inForMaTion

used in the iterative calculation process. to the INTVCC and PGND IC pins is highly recommended. current required by MOSFET gate drivers. where θJA (in °C/W) is the package thermal impedance. operating in continuous mode at maximum VIN. to 0.47µF, X5R or X7R ceramic capacitor is adequate. Figure 10. Normalized RDS(ON) vs Temperature

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ing that these components be placed adjacently.

37911faFor more information www.linear .com/L T3791-1 Efficiency Considerations The power efficiency of a switching regulator is equal to the output power divided by the input power times 100%. It is often useful to analyze individual losses to determine what is limiting the efficiency and which change would produce the most improvement. Although all dissipative elements in circuits produce losses, four main sources account for most of the losses in LT3791-1 circuits: 1. DC I2R losses. These arise from the resistances of the MOSFETs, sensing resistor, inductor and PC board traces and cause the efficiency to drop at high output currents. 2. T ransition loss. This loss arises from the brief amount of time switch M1 or switch M3 spends in the saturated region during switch node transitions. It depends upon the input voltage, load current, driver strength and MOSFET capacitance, among other factors. The loss is significant at input voltages above 20V and can be estimated from: T ransition Loss ≈ 2.7 • VIN2 • IOUT • CRSS • f where CRSS is the reverse-transfer capacitance. 3. INTVCC current. This is the sum of the MOSFET driver and control currents. 4. CIN and COUT loss. The input capacitor has the difficult job of filtering the large RMS input current to the regu- lator in buck operation. The output capacitor has the difficult job of filtering the large RMS output current in boost operation. Both CIN and COUT are required to have low ESR to minimize the AC I2R loss and sufficient capacitance to prevent the RMS current from causing additional upstream losses in fuses or batteries. 5. Other losses. Schottky diode D3 and D4 are respon - sible for conduction losses during dead time and light load conduction periods. Inductor core loss occurs predominately at light loads. Switch M3 causes reverse recovery current loss in boost operation. When making adjustments to improve efficiency, the input current is the best indicator of changes in efficiency. If you make a change and the input current decreases, then the efficiency has increased. If there is no change in the input current, then there is no change in efficiency. PC Board Layout Checklist The basic PC board layout requires a dedicated ground plane layer. Also, for high current, a multilayer board provides heat sinking for power components. n The PGND ground plane layer should not have any traces and it should be as close as possible to the layer with power MOSFETs. n Place CIN, switch M1, switch M2 and D1 in one compact area. Place COUT, switch M3, switch M4 and D2 in one compact area. n Use immediate vias to connect the components (in- cluding the LT3791-1’s SGND and PGND pins) to the ground plane. Use several large vias for each power component. n Use planes for VIN and VOUT to maintain good voltage filtering and to keep power losses low. n Flood a ll unused areas on all layers with copper. Flooding with copper will reduce the temperature rise of power components. Connect the copper areas to any DC net IN or PGND). n Separate the signal and power grounds. All small-signal components should return to the SGND pin at one point, which is then tied to the PGND pin close to the sources of switch M2 and switch M3. n Place switch M2 and switch M3 as close to the control- ler as possible, keeping the PGND, BG and SW traces short. n Keep the high dV/dT SW1, SW2, BST1, BST2, TG1 and TG2 nodes away from sensitive small-signal nodes. applicaTions inForMaTion

37911fa For more information www.linear .com/L T3791-1 applicaTions inForMaTion n The path formed by switch M1, switch M2, D1 and the CIN capacitor should have short leads and PC trace lengths. The path formed by switch M3, switch M4, D2 and the C OUT capacitor also should have short leads and PC trace lengths. n The output capacitor (–) terminals should be connected as close as possible to the (–) terminals of the input capacitor. n Connect the top driver bootstrap capacitor, C1, closely to the BST1 and SW1 pins. Connect the top driver bootstrap capacitor, C2, closely to the BST2 and SW2 pins. n Connect the input capacitors, CIN, and output capacitors, COUT, closely to the power MOSFETs. These capaci- tors carry the MOSFET AC current in boost and buck operation. n Route SNSN and SNSP leads together with minimum PC trace spacing. Avoid sense lines pass through noisy areas, such as switch nodes. Ensure accurate current sensing with Kelvin connections at the SENSE resistor. n Connect the VC pin compensation network close to the IC, between VC and the signal ground pins. The capaci- tor helps to filter the effects of PCB noise and output voltage ripple voltage from the compensation loop. n Connect the INTVCC bypass capacitor, CVCC, close to the IC, between the INTVCC and the power ground pins. This capacitor carries the MOSFET drivers’ current peaks. An additional 0.1µF ceramic capacitor placed immediately next to the INTV CC and PGND pins can help improve noise performance substantially.

37911faFor more information www.linear .com/L T3791-1 98% Efficient 60W (12V 5A) Voltage Regulator Runs Down to 3V VIN Typical applicaTions Efficiency vs Load Current Maximum Output Current vs VIN

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LOAD CURRENT (A) 0 1 EFFICIENCY (%) 100 2 3 4 5 VIN = 3V VIN = 6V VIN = 12V VIN = 28V VIN = 48V INPUT VOLTAGE (V) MAXIMUM OUTPUT CURRENT (A)1 5 7 9 20

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100µF 35V VIN 3V TO 55V STARTS UP FROM 5.5V INTVCC TG1 BG1 SNSP SNSN BST1 BST2 BG2 PGND SW2 TG2 RT L T3791-1 SWI 1µF 470nF IVINP VIN IVINN IVINMON ISMON CLKOUT PWMOUT TEST1 EN/UVLO OVLO VREF PWM CTRL 84.5k 300kHz VCSYNC SS SGND 866k 576k RFAUL T 100k 57.6k 50/uni03A9 RIN 0.003/uni03A9 0.1µF CSS 33nF CC 22nF

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0.004/uni03A9 ISP ISN FB 0.1µF L1, 6.8µH 0.1µF D2 D1 CVCC 4.7µF COUT 10µF 25V CIN 4.7µF 100V R OUT 0.015/uni03A9 VOUT 12V V O 73.2k 8.06k RC 5.1k D1, D2: NXP BAT46WJ D3: IRF 10BQ060 D4: IRF 10BQ040 D5, D6: DIODES INC. BAT46W L1: WURTH ELEKTRONIK WE-HCI 7443556680 M1, M2: RENASAS RJK0651DPB 60V DS M3, M4: VISHAY SiR424DP 40VDS COUT2: SUNCON 35HVT100M VO SHORT C/10 CCM INTVCC 100k R10 200k

37911fa For more information www.linear .com/L T3791-1 4.75 (.187) REF FE38 (AA) TSSOP REV C 0910 0.09 – 0.20 (.0035 – .0079) 0° – 8° 0.25 REF 0.50 – 0.75 (.020 – .030) 4.30 – 4.50* (.169 – .177) 1 19 REF 9.60 – 9.80* (.378 – .386) 1.20 (.047) MAX 0.05 – 0.15 (.002 – .006) 0.50 (.0196) BSC 0.17 – 0.27 (.0067 – .0106) TYP RECOMMENDED SOLDER PAD LAYOUT 0.315 ±0.05

0.50 BSC

4.50 REF

6.60 ±0.10 1.05 ±0.10

4.75 REF

2.74 REF

2.74 (.108) MILLIMETERS (INCHES) *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.150mm (.006") PER SIDE NOTE: 1. CONTROLLING DIMENSION: MILLIMETERS 2. DIMENSIONS ARE IN 3. DRAWING NOT TO SCALE SEE NOTE 4 4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT 6.40 (.252) BSC 38-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1772 Rev C) Exposed Pad Variation AA package DescripTion Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.

37911faFor more information www.linear .com/L T3791-1 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 12/13 Clarified TG1, TG2, t OFF(MIN) parameters Clarified Typical Application schematic 23, 26

37911fa For more information www.linear .com/L T3791-1  LINEAR TECHNOLOGY CORPORATION 2012 LT 1213 REV A • PRINTED IN USA Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear .com/L T3791-1 relaTeD parTs Typical applicaTion PART NUMBER DESCRIPTION COMMENTS LT3791 60V, 4-Switch, Synchronous Buck-Boost LED Driver Controller VIN: 4.7V to 60V, VOUT Range: 1.2V to 60V, T rue Color PWM™, Analog, ISD < 1µA, TSSOP-38E Packages LT C

3780 High Efficiency, Synchronous, 4-Switch Buck-Boost

V IN: 4V to 36V, VOUT Range: 0.8V to 30V, ISD < 55µA, SSOP-24, QFN-32 Packages LTC3789 High Efficiency, Synchronous, 4-Switch Buck-Boost Controller V IN: 4V to 38V, VOUT Range: 0.8V to 38V, ISD < 40µA, 4mm × 5mm QFN-28, SSOP-28 Packages LT3755/LT3755-1 LT3755-2 High Side 60V, 1MHz LED Controller with T rue Color 3000:1 PWM Dimming VIN: 4.5V to 40V, VOUT Range: 5V to 60V, 3000:1 T rue Color PWM, Analog, ISD < 1µA, 3mm × 3mm QFN-16, MSOP-16E Packages LT3756/LT3756-1 LT3756-2 High Side 100V, 1MHz LED Controller with T rue Color 3000:1 PWM Dimming VIN: 6V to 100V, VOUT Range: 5V to 100V, 3000:1 T rue Color PWM, Analog, ISD < 1µA, 3mm × 3mm QFN-16, MSOP-16E Packages LT3596 60V, 300mA Step-Down LED Driver VIN: 6V to 60V, VOUT Range: 5V to 55V, 10000:1 T rue Color PWM, Analog, ISD < 1µA, 5mm × 8mm QFN-52 Package LT3743 Synchronous Step-Down 20A LED Driver with Thee-State LED Current Control VIN: 5.5V to 36V, VOUT Range: 5.5V to 35V, 3000:1 T rue Color PWM, Analog, ISD < 1µA, 4mm × 5mm QFN-28, TSSOP-28E Packages 2.5A Buck-Boost 36V SLA Battery Charger 50/uni03A9 470nF PVIN 9V TO 58V INTVCC TG1 BG1 SNSP SNSN BST1 BST2 BG2 PGND SW2 TG2 RT L T3791-1 SWI RIN 0.003/uni03A9 SHORT IVINN IVINP 1µF VIN IVINMON PWMOUT ISMON CLKOUT EN/UVLO OVLO INTVCC 200k VREF PWM CTRLCHARGE CURRENT CONTROL SGND 84.5k 300kHz D1, D2: BAT46WJ L1: COILCRAFT SER2915L-103K M1-M4: RENESAS RJK0651DPB M5: NXP NX7002AK C IN2: NIPPON CHEMI-CON EMZA630ADA101MJA0G COUT2: SUNCON 50HVT220M VCSYNCSS C/10 CCM 20k 50/uni03A9 INTVCC 57.6k 30.9k 499k 0.1µF 22nF 22nF 1µF

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100µF 63V RSENSE 0.004/uni03A9 ISP ISN FB RBAT 0.04/uni03A9 2.5A CHARGE 36V SLA BATTERY AGM TYPE 41V FLOAT 44V CHARGE AT 25°C 0.1µF 0.1µF L1 10µH 4.7µF D2D1 COUT2 220µF 50V COUT 4.7µF 50V 1.00M 30.1k402k M52.2k CIN 4.7µF 100V TEST1 100k