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LTC2953

2953f

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.

ON/OFF

VIN

RST

LTC2953-2

499k

100k

2953 F19

RST

100k

R11

510k

3.3V

TO LOAD

200ms

0.5V

ON/OFF

VIN

RST

LTC2953-2

DC/DC

866k

200k

2953 F20

PFI

PFO

100k

DC/DC

R15

604k

R16

200k

SHDN

VOUT

VIN

1.8V

2.5V

3.3V

VTH = 2.66V

VTH = 2.01V

3.3V

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 VIN, V1 disconnects ﬁrst. When V1 decays to 2.66V, V2

is immediately disabled (there is no 200ms delay from VM

⎯R⎯S⎯T during power down). When V2 decays to 2V, V3 is

immediately disabled. See Figure 21 timing diagram.

32ms

200ms

2953 F21

POWER ON

POWER OFF

80%

Figure 19. Push Button Controlled μP Reset

Figure 21. Push Button Controlled Supply Sequence Timing

Figure 20. Push Button Controlled Supply Sequencing

LTC2953 Datasheet(PDF) 17 Page - Linear Technology

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