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Notice: The information in this document is subject to change without notice

ASM690A / 692A

ASM802L / 802M

ASM805L

µP Power Supply Supervisor With Battery Backup Switch

rev 1.0

October 2003

Monitoring Capabilities Of The Power-fail Input:

Although designed for power supply failure monitoring, the

PFI pin can be used for monitoring any voltage condition that

can be scaled by means of a resistive divider. An example is

the negative power supply monitor configured in Figure 8. In

this case a good negative supply will hold the PFI pin below

1.25V and the PFO pin will be at logic “0”. As the negative

voltage declines, the voltage at the PFI pin will rise until it

exceeds 1.25V and the PFO pin will go to logic “1”.

PFI

GND

V-

PFO

+5V

ASM690A

ASM692A

ASM802L

ASM802M

ASM805L

+5V

PFO

0V

V-

0V

51.25

–

-------------------

–

-------------------------------

=

Figure 8: Using PFI To Monitor Negative Supply Voltage