ASM705/706/707/708

April 2008

ASM813L

rev 1.6

Low Power µP Supervisor Circuits

6 of 15

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

Monitoring a Negative Voltage

The Power-Fail circuitry can also monitor a negative

supply rail. When the negative rail is OK, PFO will be

LOW, and when the negative rail is failing (not negative

enough), PFO goes HIGH (the opposite of when positive

voltages are monitored). To trigger a reset, these outputs

need to be inverted: adding the resistors and transistor as

shown achieves this. The RESET output will then have

the same sense as for positive voltages: good = HIGH,

bad = LOW. It should be noted that this circuit’s accuracy

the resistors.