stm1404c STMicroelectronics, stm1404c Datasheet - Page 16

• Manufacturer Part Number: stm1404c
• Description: Security Supervisor With Battery Switchover
• Manufacturer: STMicroelectronics

Applications information
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Table 3.
The Power-fail Input (PFI) is compared to an internal reference voltage (independent from
the V
Output (PFO) will go low. This function is intended for use as an undervoltage detector to
signal a failing power supply. Typically PFI is connected through an external voltage divider
(see
regulated output of the V
voltage at PFI falls below V
STM1404 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
power returns, the power-fail comparator is enabled and PFO follows PFI. If the comparator
is unused, PFI should be connected to V
connected to MR so that a low voltage on PFI will generate a reset output.
These Supervisor circuits are not short-circuit protected. Shorting V
excluding power-up transients such as charging a decoupling capacitor - destroys the
device. Decouple both V
the device as possible.
Vccsw
Figure 4 on page
V
V
V
RST
V
PFO
RST
BLD
V
Pin
PFI
MR
OUT
REF
TPU
BAT
CC
Figure 9 on page
comparator). If PFI is less than the power-fail threshold (V
I/O status in battery back-up
Connected to V
Disconnected from V
Disabled
Logic low
Disabled
Logic low
Connected to V
Logic high
Pulled to V
Logic high
Connected to V
9) to either the unregulated DC input (if it is available) or the
CC
CC
SS
17). This occurs after V
PFI
and V
regulator. The voltage divider can be set up such that the
below 2.4V (V
OUT
BAT
BAT
several milliseconds before the regulated V
through internal switch
through an internal switch
BAT
OUT
pins to ground by placing 0.1µF capacitors as close to
SS
SW
)
and PFO left unconnected. PFO may be
Status
CC
drops below V
PFI
OUT
SW
), the Power-Fail
(~2.4V). When
to ground -
CC
input to the