Linear Technology LTC2924 Quad Supply Sequencer DC818A DC818A Data Sheet

LTC2924

8

2924fb

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 

sequenced by a single LTC2924 (see Figure 1). An inter-

nally regulated charge pump provides (V

CC

 + 5V) gate 

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

MOSFETs. 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, C

TMR

 

(see Figure 2). When the voltage 

on this capacitor exceeds 1V, a comparator signals the 

DONE

*TMR IS CAPACITOR ADJUSTABLE

0V

ON

TMR*

V

PS2(ON)

V

PS3(ON)

V

PS4(ON)

V

PS1(ON)

PS1

PS3

PS2

PS4

V

PS4(OFF)

V

PS3(OFF)

V

PS2(OFF)

2924 F01

V

PS1(OFF)

ON

TMR

OUT1

0.61V

0.61V

1V

OUT2

OUT3

OUT4

IN1

IN2

IN3

IN4

DONE

0.61V

0.61V

0.61V

2924 F02