LTC2924 Linear Technology, LTC2924 Datasheet - Page 7

• Manufacturer Part Number: LTC2924
• Description: Quad Power Supply Sequencer
• Manufacturer: Linear Technology

OPERATIO
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
quenced by a single LTC2924 (see Figure 1). An internally
regulated charge pump provides (V
for driving external logic-level and sub-logic level MOS-
FETs. Adding a single capacitor enables an adjustable
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
on this capacitor exceeds 1V, a comparator signals the
TMR*
DONE
ON
0V
*TMR IS CAPACITOR ADJUSTABLE
U
TMR
V
(see Figure 2). When the voltage
PS2(ON)
V
PS1(ON)
Figure 1. Power On and Power Off Sequence for Four Supplies
CC
+ 5V) gate voltages
V
PS3(ON)
V
PS4(ON)
time
se-
PS1
PS3
PS2
PS4
DONE
OUT1
OUT2
OUT3
OUT4
TMR
IN1
IN2
IN3
IN4
ON
Figure 2. On Sequence for Four Supplies
0.61V
V
0.61V
PS4(OFF)
0.61V
V
PS3(OFF)
0.61V
V
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PS2(OFF)
0.61V
1V
LTC2924
V
PS1(OFF)
2924 F01
2924fa
7
2924 F02