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LT3791-1

60V 4-Switch Synchronous Buck-Boost Controller

Linear Technology 

LT3791-1

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 VC 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 INTVCC. 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 INTVCC 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.

VC (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 VC 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.

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For more information www.linear.com/LT3791-1

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