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

EN

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.

EN

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