LT8640 datasheet(9/22 Pages) AD

9 / 22 page

LT8644S

Rev. 0

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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 22): 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 AGND to com-

pensate the control loop.

PG (Pin 23): The PG pin is the open-drain output of an

internal comparator. PG remains low until the FB pin is

within ±7.75% of the final regulation voltage, and there

are no fault conditions. PG is also pulled low when EN/

UV is below 0.98V, INTVCC has fallen too low, SVIN is

too low, or thermal shutdown. PG is valid when SVIN is

above 2.7V.

FB (Pin 24): The LT8644S regulates the FB pin to 0.6V.

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.

BLOCK DIAGRAM

PIN FUNCTIONS

8644S BD

–

SLOPE COMP

INTERNAL 0.6V REF

OSCILLATOR

300kHz TO 3.5MHz

BURST

DETECT

PLL

3.6V

REG

CBST

0.1µF

COUT

VOUT

8–12

BST

SWITCH LOGIC

AND

ANTI-SHOOT

THROUGH

ERROR

AMP

SHDN

±7.75%

SHDN

THERMAL SHDN

INTVCC UVLO

SVIN UVLO

SHDN

THERMAL SHDN

SVIN UVLO

EN/UV

0.98V

–

INTVCC

PVIN

13, 14, 15

PGND

6, 12, 25–28

CLKOUT

PHMODE

OPT

CSS

OPT

VOUT

2µA

60k

AGND

SYNC/MODE

INTVCC

PVIN

5, 6

VIN

CIN1

1µF

CIN3

CIN2

1µF

CVCC

1µF

600k

60k

INTVCC

600k

SVIN

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