LTC2953 Datasheet, PDF (17/20 Pages) Linear Technology – Push Button On/Off Controller with Voltage Monitoring

LTC2953
TYPICAL APPLICATIONS
Push Button Controlled μP Reset
The circuit of Figure 19 can be used to keep a μP in reset
for 200ms after the push button has enabled system power.
After system power has stabilized, the voltage monitor
input continues to monitor the supply at the load end.
TO LOAD
3.3V
R5
100k
PB
ON/OFF
PB
V_IN
EN
VM
LTC2953-2
RST
2953 F19
R9
100k
R3
499k
R2
R11
100k 510k
Push Button Controlled Supply Sequencing
The circuit in Figure 20 uses the LTC2953-2 to sequence
3 supply rails. Power on sequencing begins by pressing
the push button for 32ms. This asserts the ^⎯E^⎯N output low,
which turns on the V1 supply. 200ms after V1 reaches 80%
of its final value (2.66V), the V2 supply is enabled. When
the V2 DC voltage reaches 80% of its final value (2V), the
V3 supply is enabled. Note that there is no internal delay
from the ^⎯P^⎯F^⎯I input to the ^⎯P^⎯F^⎯O output and so V3 is enabled
at the same time V2 rises above 2V.
A power down supply sequence begins when any of these
inputs is asserted: ^⎯P^⎯B , UVLO or ^⎯K^⎯I^⎯L^⎯L . When ^⎯E^⎯N pulls up
to V_IN, V1 disconnects first. When V1 decays to 2.66V, V2
is immediately disabled (there is no 200ms delay from VM
to ^⎯R^⎯S^⎯T during power down). When V2 decays to 2V, V3 is
immediately disabled. See Figure 21 timing diagram.
0.5V
VM
200ms
RST
Figure 19. Push Button Controlled μP Reset
3.3V
ON/OFF
R5
R9
100k 100k
V_IN
EN
R3
866k
PB
VM
LTC2953-2
V_TH = 2.66V _R2
200k
RST
V_TH = 2.01V
PFI
V_IN
DC/DC
#1
SHDN ^VOUT
PB
EN
V1
3.3V
V1
V2
POWER ON
32ms
80%
200ms
80%
POWER OFF
80%
80%
V3
2953 F21
Figure 21. Push Button Controlled Supply Sequence Timing
V2
2.5V
R15
604k
R16
200k
V_IN
PFO
2953 F20
DC/DC
#2
SHDN ^VOUT
V3
1.8V
Figure 20. Push Button Controlled Supply Sequencing
2953f
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