LTC2924C(RevA) データシートの表示（PDF） - Linear Technology

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LTC2924C
(Rev.:RevA)

Quad Power Supply Sequencer

Linear Technology 

U

OPERATIO

PS1

VPS1(ON)

LTC2924

PS3

VPS3(ON)

0V

TMR*

ON

VPS2(ON)

PS2

PS4

VPS4(ON)

VPS4(OFF)

VPS3(OFF)

VPS2(OFF)

VPS1(OFF)

DONE *TMR IS CAPACITOR ADJUSTABLE

2924 F01

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

The LTC2924 is a power supply sequencer designed for

ON

0.61V

use with external N-channel MOSFETs or power supplies

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

1V

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

regulated charge pump provides (VCC + 5V) gate voltages OUT1

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

FETs. Adding a single capacitor enables an adjustable time IN1

0.61V

delay between power supplies during both Power On and

Power Off sequencing. A second capacitor can be added OUT2

to enable a power good timer which detects the failure of

any power supply to turn on within the set time.

IN2

0.61V

The ON pin signal is used to command the LTC2924

to start the Power On and Power Down sequences. To OUT3

command the Power On sequence, the ON pin is pulled

IN3

above 0.61V by a system controller or a resistive divider

from a power supply. A voltage comparator senses the OUT4

ON command and signals the sequencing logic to start

the Power On sequence.

IN4

0.61V

0.61V

When the Power On sequence starts, the TMR grounding

switch is released and a 5µA current source charges an DONE

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

on this capacitor exceeds 1V, a comparator signals the

2924 F02

Figure 2. On Sequence for Four Supplies

2924fa

7

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