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LTC2924CGN#PBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P22
LTC2924
7
2924fc
For more information www.linear.com/LTC2924
FuncTional DiagraM
–
+
0.61V
ON
–
+
0.61V
IN1
–
+
0.61V
IN2
–
+
0.61V
IN3
–
+
–
+
I
H
0.61V
0.5V
HYS/CFG
IN4
V
CP
10µA
OUT1
V
CC
V
CP
10µA
OUT2
V
CP
10µA
OUT3
V
CP
10µA
OUT4
DONE
V
CP
FAULT
2924 BD
LAST
1V
–
+
1V
TMR
PGT GND
FIRST
DETECT
LOGIC
CHARGE
PUMP
5
CLOCK
UVLO
1V
0.5V
0.61V
INTERNAL
REFERENCE
I
H
I
H
I
H
I
H
I
H
5µA 5µA
16
1
2
3
4
15
14
12 13
11
9
10
8
7
6
5
4
LTC2924
8
2924fc
For more information www.linear.com/LTC2924
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
Figure 1. Power On and Power Off Sequence for Four Supplies
Figure 2. On Sequence for Four Supplies
operaTion
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
LTC2924
9
2924fc
For more information www.linear.com/LTC2924
operaTion
logic, which starts the charge pump and enables OUT1
to turn on the first power supply. The power good timer
circuit is also enabled by turning off the switch that is
shorting the external capacitor to ground and enabling a
5µA current source to charge the C
PGT
capacitor.
The output circuit responds by opening a switch, which
is shorting the OUT1 pin to ground and enabling a 10µA
current source, which is connected to the charge pump.
The OUT1 pin can be connected to either the shutdown pin
of a power supply or the gate of a N-channel MOSFET that
is in series with the output of the sequenced power supply.
As the power supply turns on, the resistive divider con-
nected to the IN1 pin starts to drive up the voltage at the
IN1 pin. When the voltage at this pin exceeds 0.61V, the
comparator signals the logic that the first power supply
is on. At this time a current is sourced out of the IN1
pin which serves as the hysteresis current for the input
comparator. This allows the application to choose a lower
Power Off voltage sense during the Power Off sequence.
The power good timer (PGT) circuit is signaled and resets
the PGT capacitor. The timer circuit is enabled and the
cycle repeats until the last power supply has turned on.
When the last power supply has turned on, the DONE pin
pull-down switch is turned on to signal that the Power On
sequence has completed.
If a power supply fails to turn on after it is enabled and the
voltage at the PGT pin exceeds 1V, the LTC2924 will disable
all power supplies by pulling all OUT pins to ground. A fault
condition will be indicated by the FAULT pin pulling low.
The hysteresis current sourced at the ON pin and each IN
pin is set at the HYS/CFG pin. The current is determined
by an external resistor nominally pulled to ground. The
hysteresis current is 0.5V/R
HYS
.
The Power Off sequence is initiated by pulling the ON pin
below 0.61V after a Power On sequence has completed
(see Figure 3). The Power Off sequence turns off the power
supplies in the reverse order of the Power On sequence.
OUT4 is turned off first. The timer function is used between
each supply being sequenced down. The PGT is not used.
The end of the Power Off sequence is indicated by the
LTC2924 floating the DONE pin.
Figure 3. 4-Power Supply Power Off Sequence
ON
TMR
OUT4
0.61V
0.61V
OUT3
OUT2
OUT1
IN4
IN3
IN2
IN1
DONE
0.61V
0.61V
0.61V
2924 F03
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P22

LTC2924CGN#PBF

Mfr. #:
Buy LTC2924CGN#PBF
Manufacturer:
Analog Devices Inc.
Description:
Power Management Specialized - PMIC Power Supply On/Off Sequencer
Lifecycle:
New from this manufacturer.
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