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SP791DS/08

SP791 Low Power Microprocessor Supervisory with Battery Switch-Over

© Copyright 2000 Sipex Corporation

to select another watchdog-timeout period.

Watchdog-timeout period = 2.1 x (capacitor

value in nF) ms.

Pin 9 — MR — Manual-Reset Input. This input

can be tied to an external momentary

pushbutton switch, or to a logic gate output.

RESET remains low as long as MR is held

low and for 200ms after MR returns high.

Pin 10 — LOWLINE — LOWLINE Output goes

set threshold. The output can be used to gen-

erate an NMI (nonmaskable interrupt) if the

unregulated supply is inaccessible.

Pin 11 — WDI — Watchdog Input. WDI is a three-

level input. If WDI remains either high or

low for longer than the watchdog timeout

period, WDO goes low. WDO remains low

until the next transition at WDI. Leaving

WDI unconnected disables the watchdog

function. WDI connects to an internal volt-

age divider between V

sets it to mid-supply when left unconnected.

IN

whichever occurs first.

to chip-enable gating circuit. Connect to

GND or V

Pin 14 — WDO — Watchdog Output. WDO goes

low if WDI remains either high or low longer

than the watchdog timeout period. WDO

returns high on the next transition at WDI.

WDO remains high if WDI is unconnected.

WDO is also high when RESET is asserted.

Pin 15 — RESET — RESET Output goes low

whenever V

old. RESET will remain low for 200ms

after V

power-up.

Pin 16 — WDPO — Watchdog-Pulse Output.

Upon the absence of a transition at WDI,

WDPO will pulse low for a minimum of

1ms. WDPO precedes WDO by 70ns.

PIN ASSIGNMENTS

Pin 1 — V

to external battery or capacitor and charging

circuit.

Pin 2 —V

nects to V

and V

V

reset threshold, V

nect a 0.1

µF capacitor from V

Pin 3 — V

CC

— Input Supply Voltage —

+5V input

Pin 4 — GND — Ground reference for all signals

Pin 5 — BATT ON — Battery On Output. Goes

high when V

when V

of a PNP through a current-limiting resistor

to BATT ON for V

greater than 250mA.

Pin 6 — PFO — Power-Fail Output. This is the

output of the power-fail comparator. PFO

goes low when PFI is less than1.25V. This is

an uncommitted comparator, and has no ef-

fect on any other internal circuitry.

Pin 7 — PFI — Power-Fail Input. This is the

noninverting input to the power-fail compara-

tor. When PFI is less than 1.25V, PFO goes

low. Connect PFI to GND or V

used.

Pin 8 — SWT — Set Watchdog-Timeout Input.

Connect this input to V

fault 1.6 sec watchdog timeout period. Con-

nect a capacitor between this input and GND

PINOUT

Vcc

GND

BATT ON

PFO

PFI

SWT

WDPO

RESET

WDO

WDI

LOWLINE

MR

16

DIP/SO

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