LTC2936
25
2936fa
For more information www.linear.com/LTC2936
applicaTions inForMaTion
Five Supply Power-Up Sequencer
Figure 4 illustrates how to use the LTC2936 CMPn outputs
to enable DC/DC converters sequentially, at power-up.
The system is powered by a 12V source, which is also
monitored.
The system starts-up when the pushbutton is pressed
and the LTC2950-1 takes the RUN pin of the LTM4600
high. This forces the LTM4600 to generate 5V, which also
supplies the other 4 DC/DC converters.
The LTC2936 is configured to monitor 5V on V1, 3.3V on
V2, 2.5V on V3, –5V on V4, 1.8V on V5 and 12V on V6.
When the programmed threshold is reached on V1, CMP1
pulls high, which enables the 3.3V converter. When the
programmed threshold is reached on V2, CMP2 pulls high,
which enables the 2.5V converter. When all converters have
been enabled and power is good, CMP5 pulls high. GPIO1
is configured to pull high 6.4ms after CMP5.
If the KILL input of the LTC2950-1 is not forced high within
512ms of initial power-up, EN pulls low and the LTM4600
is powered down.
In the event that the external 12V supply drops below its
programmed threshold, CMP6 and GPIO2 will pull low
after 1.6ms. The LTC2950-1 then receives a logic low on
the KILL input, which powers down the LTM4600 and the
sequencing circuit.
Figure 4. Five Supply Power-Up Sequencer
2936 F04
LTC2936
CMP1
CMP2
CMP3
CMP4
V
PWR
GPIO1
GPIO2
GPI1
CMP5
CMP6
SDA
SCL
GPI2
V1
ASEL1 V
DD33
GND
V2 V3 V4 V5 V6
LTM4600
12V
ASEL0
5V
–5V
1.8V
2.5V
3.3V
–5V
1.8V
2.5V
3.3V
5V
10k 10k 10k10k
DONE
12V STATUS
LT3704
V
IN
V
OUT
RUN/UVLO
LT3028
V
IN
V
OUT
SHDN
LT3028
V
IN
V
OUT
SHDN
LT3028
V
IN
V
OUT
SHDN
10k
10k
10k
10k
V
IN
V
OUT
GNDRUN
LTC2950-1
V
IN
EN
INT
KILLGNDPB
ON/OFF
0.1µF
10k
0.1µF
SYSTEM
270k
0.1µF
100k
1M
100k
