AN3271 datasheet(7/29 Pages) STMICROELECTRONICS

7 / 29 page

AN3271

Pin descriptions and typical application hookup

Doc ID 17933 Rev 2

7/29

Pin descriptions and typical application hookup

VCC - power supply input is monitored at startup and during operation to have sufficient

voltage.

PB - push-button input is used to start an application or assert an interrupt during normal

operation or possibly power down the application.

SR - Smart Reset button, when pressed together with PB, can either power down the

application or reset the device regardless of system response.

EN (EN) - active high or active low enable output (device ordering option) can drive various

power switches from PMOS to DC-DC converters, regulators, etc. and therefore switch

power for the application. It is asserted by a PB button press and confirmed by PSHOLD

assertion (VCC has to be above threshold the whole time). Enable output can be deasserted

by the following events:

●

Startup is not properly confirmed by PSHOLD assertion

●

PSHOLD is deasserted (driven low) during operation

●

Undervoltage condition is detected

●

Long push of PB and SR buttons is detected (valid only for devices with option “EN

deasserted by long push”)

●

PSHOLD is not asserted after reset invoked by a long push of PB and SR buttons (valid

only for devices with option “RST deasserted by long push”)

RST - system reset, output is asserted during power-up or after a long push of PB and SR

buttons simultaneously (device option).

PSHOLD - assertion of the input confirms proper power-up, deassertion disables power for

the application.

CSRD - external capacitor connected to CSRD pin determines how long the PB and SR

buttons must be held in order to recognize a long push and either reset the system or

disable the system power (based on option used), the constant is 10 s / µF.

VREF - highly precise 1.5 V voltage reference output with ±1% accuracy (can be used as

a reference for analog-digital converters, for example). A 1 µF CREF capacitor on the output

is mandatory.

AN3271 Datasheet(PDF) 7 Page - STMicroelectronics