STM1403

Operation

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Table 3.

I/O status in battery backup

3.4

Power-fail input/output

The power-fail input (PFI) is compared to an internal reference voltage (independent from

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 Figure 4 on page 9) to either the unregulated DC input (if it is available) or the

STM1403 or the microprocessor drops below the minimum operating voltage.

During battery backup, the power-fail comparator is turned off and PFO goes (or remains)

power returns, the power-fail comparator is enabled and PFO follows PFI. If the comparator

connected to MR so that a low voltage on PFI will generate a reset output.

3.5

Applications information

excluding power-up transients such as charging a decoupling capacitor - destroys the

the device as possible.

Pin

Status

PFI

Disabled

PFO

Logic low

MR

Disabled

RST

Logic low

Vccsw

Logic high

BLD

Logic high