LTC3111 datasheet(9/32 Pages) LINER

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LTC3111

3111fa

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PIN FUNCTIONS (DFN/MSOP)

COMP (Pin 1/Pin 1): Error Amp Output. An R-C network

connected from this pin to FB sets the loop compensa-

tion for the voltage converter. Refer to the Applications

Information section for component selection details.

FB (Pin 2/Pin 2): Feedback Voltage Input. Connect the

VOUTresistordividertaptothispin.Theoutputvoltagecan

be adjusted from 2.5V to 15V by the following equation:

VOUT = 0.8V • 1+









where R1 is the resistor between VOUT and FB and R2 is

the resistor between FB and GND

SNSGND (Pin 3/Pin 3): This pin must be connected to

ground.

RUN(Pin4/Pin4):InputtoEnableorDisabletheICandSet

Custom Input Undervoltage Lockout (UVLO) Thresholds.

The RUN pin can be driven by an external logic signal to

enable and disable the IC. In addition, the voltage on this

pin can be set by a resistive voltage divider connected to

the input supply in order to provide accurate turn-on and

turn-off (UVLO) thresholds determined by:

VIN(RUN) =1.2V • 1+









The IC is enabled if RUN exceeds 1.2V nominally. Once

enabled, the UVLO threshold has a built-in hysteresis of

approximately120mV,turn-offwilloccurwhenthevoltage

on RUN drops to below 1.08V nominally. To continuously

enable the IC, RUN can be tied directly to the input voltage

up to the absolute maximum rating. This pin should not

be left unconnected.

VIN (Pin 5/Pin 5): Input Supply Voltage. This pin should

be bypassed to the ground plane with at least 10µF of low

ESR, low ESL ceramic capacitance. Place this capacitor as

close to the pin as possible and provide as short a return

path to the ground plane as possible.

SW1 (Pin 6/Pin 6): The external inductor and internal

switches A and B are connected here.

BST1 (Pin 7/Pin 7): Boosted Floating Driver Supply for

A-Switch Driver. Connect a 0.1µF capacitor from this pin

to SW1.

BST2 (Pin 8/Pin 10): Boosted Floating Driver Supply for

D-Switch Driver. Connect a 0.1µF capacitor from this pin

to SW2.

SW2 (Pin 9/Pin 11): The external inductor and internal

switches C and D are connected here.

VOUT (Pin 10/Pin 12): Regulated Output Voltage. This pin

should be connected to a low ESR ceramic capacitor. The

capacitor should be placed as close to the pin as possible

and have a short return to the ground plane.

NC (Pin 11/Pin 13): Not Connected. This pin should be

connected to ground.

VCC (Pin 12/Pin 14): External Capacitor Connection for

the Regulated VCC Supply. This supply is used to operate

internal circuitry and switch drivers. VCC will track VIN up

to 4.2V typical, but will maintain this voltage when VIN >

4.2V. Connect a 1µF ceramic capacitor from this pin to

GND. This pin can be tied to an external supply up to 5.5V.

Refer to the Operation section of this data sheet under

Power VCC from an External Source for more details.

PWM/SYNC (Pin 13/Pin 15): Burst Mode Control and

Synchronization Input. A DC voltage < 0.5V commands

Burst Mode operation independent of load current, >1.5V

commands 800kHz fixed frequency mode. A digital pulse

train between 600kHz and 1.5MHz applied to this pin will

override the internal oscillator and set the operating fre-

quency. The pulse train should have a minimum high time

or low time greater than 100ns (Note 6). Note the LTC3111

has reduced power capability when operating in Burst

Mode operation. This pin should not be left unconnected.

SGND (Pin 14/Pin 16): Signal Ground. Terminate the RUN

input voltage divider and output voltage divider to SGND.

PGND(ExposedPadPin15/Pin8,9,ExposedPadPin 17)

Power Ground. The exposed pad must be soldered to

the PCB and electrically connected to ground through

the shortest and lowest impedance connection possible.

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