STM804 STMICROELECTRONICS [STMicroelectronics], STM804 Datasheet - Page 11

• Manufacturer Part Number: STM804
• Description: 3V Supervisor with Battery Switchover
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Power-fail Input/Output (NOT available on STM795)
The Power-fail Input (PFI) is compared to an inter-
nal reference voltage (independent from the V
comparator). If PFI is less than the power-fail
threshold (V
go low. This function is intended for use as an un-
dervoltage detector to signal a failing power sup-
ply. Typically PFI is connected through an external
voltage divider (see
the unregulated DC input (if it is available) or the
regulated output of the V
divider can be set up such that the voltage at PFI
falls below V
regulated V
804/805/806 or the microprocessor drops below
the minimum operating voltage.
During battery back-up, the power-fail comparator
is turned off and PFO goes (or remains) low (see
Figure 14. Power-fail Comparator Waveform (STM690/704/802/804/805/806)
PFO
V CC
V RST
V SW (2.4V)
RST
CC
PFI
PFI
), the Power-Fail Output (PFO) will
input to the STM690/704/795/802/
several milliseconds before the
Figure 11., page
PFO follows PFI
CC
regulator. The voltage
8) to either
RST
Figure 14., page
below V
er-fail comparator is enabled and PFO follows PFI.
If the comparator is unused, PFI should be con-
nected to V
may be connected to MR on the STM704/806 so
that a low voltage on PFI will generate a reset out-
put.
Applications Information
These Supervisor circuits are not short-circuit pro-
tected. Shorting V
er-up transients such as charging a decoupling
capacitor - destroys the device. Decouple both
V
pacitors as close to the device as possible.
CC
and V
SW
STM690/704/795/802/804/805/806
BAT
(2.4V). When power returns, the pow-
SS
pins to ground by placing 0.1µF ca-
and PFO left unconnected. PFO
11). This occurs after V
OUT
to ground - excluding pow-
PFO follows PFI
trec
AI08861a
CC
drops
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