Datasheet

LTC2953
16
2953f
TYPICAL APPLICATIONS
Push Button Buffer
The circuit of Figure 16 shows the power fail comparator
sensing the push button input. The
⎯
P
⎯
F
⎯
O output toggles
each time the push button crosses 0.5V. This application
provides an early warning of push button activity.
Disconnect Input Resistive Divider To Save Power
In order to prolong battery life when system power has
been turned off, the LTC2953-2 power fail comparator can
be used to disconnect the external battery monitor resistive
divider. The circuit in Figure 18 connects
⎯
P
⎯
F
⎯
I to
⎯
E
⎯
N and
⎯
P
⎯
F
⎯
O to the bottom end of the resistive divider.
PFO
2953 F16
PFI
PB
0.5V
ON/OFF
–
+
ON/OFF
ENV
IN
LTC2953-2
2953 F17
PB
R5
100k
R9
100k
12V
TO LOAD
Power Path Switching
The high voltage
⎯
E
⎯
N output of the LTC2953-2 is designed
to switch On/Off an external power PFET. This allows a
user to connect/disconnect a power supply (or battery)
to its load by toggling the
⎯
P
⎯
B pin. Figure 17 shows the
LTC2953-2 in a 12V wall adapter application.
ENV
IN
PFI
LTC2953-2
2953 F18
UVLO
PFO
R5
100k
R14
1070k
R12
110k
R9
100k
8.4V
0.5V
–
+
When the user presses the push button to turn on system
power (
⎯
E
⎯
N low), the output of the power fail comparator
asserts
⎯
P
⎯
F
⎯
O low. The low battery external resistive divider
is thus enabled to monitor the input supply. If the voltage
on the UVLO input falls to less than 0.5V, a system power
down sequence is initiated. Note that the IR drop across
the internal NFET is typically less than 0.2mV when the
UVLO pin voltage is 0.5V.
Once system power has been turned off (
⎯
E
⎯
N high), the
external resistive divider is disconnected and thus con-
sumes zero DC current.
Figure 16. Push Button Buffer
Figure 17. Power Path Switching
Figure 18. Disconnect Input Resistive Divider to Save Power