STM1404_08 datasheet(12/35 Pages) STMICROELECTRONICS

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Pin descriptions

STM1404

12/36

If a security alarm (SAL) is issued on tamper, then the state of the Vccsw pin is as follows:

STM1404A (VOUT remains ON when SAL is active-low): Vccsw pin will continue to

operate in normal mode;

STM1404B (VOUT is taken to High-Z when SAL is active-low): Vccsw pin will be set to

high when this occurs; and

STM1404C (VOUT is driven to ground when SAL is active-low): Vccsw pin will be set to

high when this occurs.

2.4

BLD, VBAT low voltage detect output (open drain)

This is an internally loaded test of the battery, activated only during a power-up sequence to

insure that the battery is good either prior to or after encapsulation of the module. There are

three customer options for VDET:

●

2.3 V (2.5 V – external diode drop of about 0.2 V) for a 3 V lithium cell

●

2.5 V (2.7 V – 0.2 V) for a 3 V lithium cell or

●

3.2 V (3.4 V – 0.2 V) for a 3.68 V lithium “AA” battery

This output pin will go active-low when it detects a voltage on the VBAT pin below VDET. BLD

will be released when VCC drops below VRST.

2.5

Active-low RST output (open drain)

Goes low and stays low when VCC drops below VRST (Reset Threshold selected by the

customer), or when MR is logic low. It remains low for trec (200ms, typical) AFTER VCC rises

above VRST and MR goes from low to high.

2.6

MR, manual reset input

A logic low on MR asserts the RST output. The RST output remains asserted as long as MR

is low and for trec after MR returns to high. This active low input has an internal 40 kΩ

(typical) pull-up resistor. It can be driven from a TTL or CMOS logic line or shorted to ground

with a switch. Leave it open if unused.

2.7

PFO, power-fail output (open drain)

When PFI is less than VPFI (power-fail input threshold voltage) or VCC falls below VSW

(battery switchover threshold ~ 2.4 V), PFO goes low, otherwise, PFO remains high. Leave

this pin open if unused.

2.8

PFI, power-fail input

When PFI is less than VPFI, or when VCC falls below VSW (see PFO, above), PFO goes

active-low. If this function is unused, connect this pin to VSS.

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