LT8640S datasheet(11/26 Pages) AD

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LT8642-1

Rev. 0

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and the internal reference resumes control of the error

amplifier. An internal 1.9µA pull-up current from INTVCC

on this pin allows a capacitor to program output voltage

slew rate. This pin is pulled to ground with an internal

200Ω MOSFET during shutdown and fault conditions; use

a series resistor if driving from a low impedance output.

This pin may be left floating if the soft-start feature is not

being used.

VC (Pin 19): The VC pin is the output of the internal error

amplifier. The voltage on this pin controls the peak switch

current. Tie an RC network from this pin to ground to

compensate the control loop.

FB (Pin 20): The LT8642-1 regulates the FB pin to 0.597V.

Connect the feedback resistor divider tap to this pin. Also,

connect a phase lead capacitor between FB and VOUT.

Typically, this capacitor is 4.7pF to 47pF.

Corner Pins: These pins are for mechanical support only

and can be tied anywhere on the PCB, typically ground.

PIN FUNCTIONS

BLOCK DIAGRAM

86421 BD

–

SLOPE COMP

INTERNAL 0.597V REF

OSCILLATOR

200kHz TO 3MHz

BURST

DETECT

3.4V

REG

CBST

COUT

VOUT

8–10

BST

SWITCH LOGIC

AND

ANTI-SHOOT

THROUGH

ERROR

AMP

SHDN

±8%

SHDN

THERMAL SHDN

INTVCC UVLO

VIN UVLO

SHDN

THERMAL SHDN

VIN UVLO

EN/UV

0.99V

–

INTVCC

BIAS

VIN

12, 13

GND

6, 11, 21

CLKOUT

OPT

CSS

OPT

VOUT

1.9µA

60k

SYNC/MODE

INTVCC

VIN

4, 5

VIN

CIN1

CIN3

CIN2

CVCC

600k

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