AN3271 datasheet(5/29 Pages) STMICROELECTRONICS

5 / 29 page

AN3271

Basic functionality

Doc ID 17933 Rev 2

5/29

Basic functionality

1.1

Safe power-up

If the system is off, press the PB button to safely power up. EN output is asserted and power

for the application is enabled. Proper power-up has to be confirmed from a processor by

PSHOLD assertion, otherwise EN is deasserted.

1.2

Interrupt assertion

If the device is on, press the PB button to assert an interrupt to the processor. The

processor can then perform backup routines and prepare the application for shutdown,

reset, display the menu, etc.

1.3

Power-down after long push (optional)

If the application is not responding to the interrupt (e.g. program freezes), press the PB

button and SR button simultaneously to power down the application regardless of processor

response. The time needed for both buttons to be held is adjustable by external capacitor

CSRD.

Figure 2.

Simplified timing sequence for option “enable deasserted after long push”

For successful power-up the battery voltage has to be above VTH+ threshold.

AN3271 Fiches technique(PDF) 5 Page - STMicroelectronics