Datasheet

LTC2924
11
2924fb
applicaTions inForMaTion
a Power On sequence (V
ON
) and Off during a Power Off
sequence
(V
OFF
).
Referring to Figures 5 and 6, each set of resistors can
then be calculated by:
R
B
=
V
ON
– V
OFF
I
HYS
R
A
=
R
B
• 0.61V
V
ON
– 0.61V
In the following example (Figure 5) I
HYS
is 50µA. This
corresponds to a R
HYS
resistor of:
R
HYS
=
0.5V
50µA
= 10kΩ
In Figure 5, V
ON
= 2.2V and V
OFF
= 1V. Using the equations
provided above:
R
B
=
2.2V – 1V
50µA
= 24kΩ
R
A
=
24kΩ • 0.61V
2.2V – 0.61V
= 9.2kΩ
Hysteresis Voltage Check
After calculating the resistors R
B
and R
A
, check to make
sure the hystersis voltage at the ON and IN1-IN4 pins is
greater than 4mV. Use the following equation:
V
HYS
=
V
ON
– V
OFF
( )
•R
A
R
A
+R
B
For this example:
V
HYS
=
2.2V – 1V
( )
• 9.2kΩ
9.2k
Ω +
24k
Ω
= 0.33V
which is greater than 4mV.
Figure 5. Designing I
HYS
, Feedback Resistors
Figure 6. Typical Power Supply Sequencer
+
–
IN
R
B
V
PS
R
A
0.61V
I
RB
V
ON
= 2.2V
V
OFF
= 1V
I
FB
= I
RB
+ I
HYS
2924 F05
I
HYS
I
HYS
150nF
2924 TA03
SYSTEM
CONTROLLER
150nF
POWER SUPPLY 4
POWER SUPPLY 3
POWER SUPPLY 2
POWER SUPPLY 1
V
ON
≥ 3.01V
V
OFF
≤ 2.68V
V
ON
≥ 4.49V
V
OFF
≤ 3.99V
V
ON
≥ 1.43V
V
OFF
≤ 1.27V
V
ON
≥ 2.25V
V
OFF
≤ 2V
33.2k
9.31k
24.9k
0.1µF
15.8k 49.9k
11.81k 7.87k 8.45k
49.9k
2.5V
SHDN
1.6V
SHDN
5V
SHDN
3.3V
SHDN
10k
5V EARLY*
10k
*5V EARLY MUST BE ON BEFORE
SEQUENCING SUPPLIES
OUT1
OUT2
OUT3
OUT4
ON
DONE
FAULT
TMR
PGT
IN1
IN2
IN3
IN4
HYS/CFG
V
CC
GND
LTC2924