April 2008
rev 1.6
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
depends on the V
CC
line, the PFI threshold tolerance, and
the resistors.
ASM705/706/707/708
ASM813L
Low Power µP Supervisor Circuits
Notice: The information in this document is subject to change without notice.
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PULSECORE [ PulseCore Semiconductor ]
