ASM813LCPA ALSC [Alliance Semiconductor Corporation], ASM813LCPA Datasheet - Page 6

• Manufacturer Part Number: ASM813LCPA
• Description: Low Power UP Supervisor Circuits
• Manufacturer: ALSC [Alliance Semiconductor Corporation]

ASM705 / 706 / 707 / 708
ASM813L
July 2004
rev 1.2
Monitoring a Negative Voltage
V
The Power-Fail circuitry can also monitor a negative supply
CC
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
R
R
1
3
monitored). To trigger a reset, these outputs need to be
V
CC
inverted: adding the resistors and transistor as shown
MR
achieves this. The RESET output will then have the same
R
4
sense as for positive voltages: good = HIGH, bad = LOW. It
ASM70X
2N3904
PFO
PFI
should be noted that this circuit’s accuracy depends on the
R
2
V
line, the PFI threshold tolerance, and the resistors.
CC
To µP
RESET
GND
V
- 1.25
1.25 - VTRIP
CC
=
Negative Input Voltage
R
R
2
1
Figure 5: Monitoring a negative voltage
6 of 15
Low Power µP Supervisor Circuits
Notice: The information in this document is subject to change without notice