LT8335 datasheet(7/34 Pages) AD

7 / 34 page

LT8357

Rev. 0

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PIN FUNCTIONS

VC: Error Amplifier Compensation. Place an external RC

network to compensate the control loop.

FB: Output Voltage Feedback Input. Tie this pin to a resis-

tor divider from the output to ground to set the output

regulation voltage. The FB pin is regulated to 1V during

normal operation.

PGOOD: Power Good Open Drain Output. The PGOOD

pin is pulled low when the FB pin is beyond ±8% of the

final regulation voltage. To function, the pin requires an

external pull-up resistor.

SS: Soft-Start Timer Setting. Connect a capacitor between

this pin and ground to set the output soft-start time. An

internal 15µA pull-up current charging the SS capacitor

gradually ramps up FB regulation voltage. UVLO or ther-

mal shutdown immediately pulls SS pin to ground and

stops switching.

RT: Switching Frequency Setting. Connect a resistor from

this pin to ground to set the internal oscillator frequency

from 100kHz to 2MHz.

SYNC/MODE: External Frequency Synchronization and

Operation Mode Selection. This pin allows five selectable

modes for optimization of performance:

1. External clock: For external frequency synchronization

and pulse-skipping mode at light load.

2. INTVCC: For spread spectrum frequency modulation

and pulse-skipping mode at light load.

3. Float: For internal oscillator frequency and pulse-

skipping mode at light load.

4. 100kΩ resistor to GND: For spread spectrum fre-

quency modulation and low-ripple Burst Mode at light

load.

5. GND: For internal oscillator frequency and low-ripple

Burst Mode at light load.

SENSE: Current Sense Comparator Input. Kelvin connect

this pin to the positive terminal of the current sense resis-

tor in the source of the bottom MOSFET. The negative

terminal of the current sense resistor should be connected

to ground plane close to the chip.

GATEP: MOSFET Gate Pull-Up Drive. Drives the gate of

N-Channel MOSFET with a voltage swing from ground to

INTVCC.

GATEN: MOSFET Gate Pull-Down Drive. Drives the gate

of N-Channel MOSFET with a voltage swing from ground

to INTVCC.

INTVCC: Internal 5V Linear Regulator Output. Supplied

from VIN pin, the INTVCC linear regulator powers internal

control circuitry and gate driver. Do not load the INTVCC

pin with external circuitry. Locally bypass this pin to

ground with a minimum 2.2µF ceramic capacitor.

EN/UVLO: Enable and Undervoltage Lockout. Force the

pin below 0.3V to shut down the part and reduce VIN qui-

escent current below 3µA. Force the pin above its accurate

enable threshold to enable the part. The accurate enable

threshold can be used to program an undervoltage lock-

out (UVLO) threshold with a resistor divider from VIN to

ground. If neither function is used, tie this pin to VIN.

VIN: Input Supply. The VIN pin is normally tied to the

power input supply or the boost converter output, and

supplies INTVCC linear regulator. Locally bypass this pin

to ground with a 0.1µF ceramic capacitor.

GND (Exposed Pad): Ground. Solder the exposed pad

directly to the ground plane.

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