LTC2924IGN datasheet(7/20 Pages) LINER

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LTC2924

2924fa

The LTC2924 is a power supply sequencer designed for

use with external N-channel MOSFETs or power supplies

with shutdown pins. Four power supplies can be fully se-

quenced by a single LTC2924 (see Figure 1). An internally

regulated charge pump provides (VCC + 5V) gate voltages

for driving external logic-level and sub-logic level MOS-

FETs. Adding a single capacitor enables an adjustable time

delay between power supplies during both Power On and

Power Off sequencing. A second capacitor can be added

to enable a power good timer which detects the failure of

any power supply to turn on within the set time.

The ON pin signal is used to command the LTC2924

to start the Power On and Power Down sequences. To

command the Power On sequence, the ON pin is pulled

above 0.61V by a system controller or a resistive divider

from a power supply. A voltage comparator senses the

ON command and signals the sequencing logic to start

the Power On sequence.

When the Power On sequence starts, the TMR grounding

switch is released and a 5µA current source charges an

external capacitor, CTMR(see Figure 2). When the voltage

on this capacitor exceeds 1V, a comparator signals the

OPERATIO

Figure 1. Power On and Power Off Sequence for Four Supplies

DONE

*TMR IS CAPACITOR ADJUSTABLE

TMR*

VPS2(ON)

VPS3(ON)

VPS4(ON)

VPS1(ON)

PS1

PS3

PS2

PS4

VPS4(OFF)

VPS3(OFF)

VPS2(OFF)

2924 F01

VPS1(OFF)

Figure 2. On Sequence for Four Supplies

TMR

OUT1

0.61V

OUT2

OUT3

OUT4

IN1

IN2

IN3

IN4

DONE

0.61V

2924 F02

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