SP791DS/08

SP791 Low Power Microprocessor Supervisory with Battery Switch-Over

© Copyright 2000 Sipex Corporation

8

2) Manual-Reset input ¬ Manually resets

RESET output

3) Power Fail Comparator ¬ Provides for power-

fail warning and low-battery detection, or

monitors another power supply.

4) Watchdog function ¬ Monitors

µP activity

where the watchdog output goes to a logic

LOW state if the watchdog input is not toggled

for a period greater than the timeout period.

5) Internal switch ¬ Switches over from V

V

old and below V

MANUAL RESET INPUT

Many microprocessor or microcontroller prod-

ucts include manual-reset capability, allowing

the operator or test technician to initiate a reset.

The Manual Reset Input (MR) can be connected

directly to a switch, without an external pull-up

resistor. It connects to a 1.25V comparator, and

ure 1. The propagation delay from asserting MR

to RESET being asserted is 7us typical. Pulsing

FEATURES

The SP791 is a microprocessor (

µP) supervi-

sory circuit that monitors the power supplied to

digital circuits such as microprocessors,

microcontrollers, or memory. The SP791 is an

ideal solution for portable, battery-powered

equipment that require power supply monitor-

ing. The SP791 watchdog functions will con-

tinuously oversee the operational status of a sys-

tem. Implementing the SP791 will reduce the

number of components and overall complexity

in a design that requires power supply monitor-

ing circuitry. The operational features and ben-

efits of the SP791 are described in more detail

below.

THEORY OF OPERATION

The SP791 is a complete

µP supervisor IC and

provides the following main functions:

1)

µP reset ¬ RESET output is asserted during

power fluctuations such as power-up, power-

down, and brown out conditions, and is guar-

to 1V.

Figure 2. Manual-Reset Timing Diagram

Typical Operating Circuit

Figure 3. Diode "OR" connections allow multiple reset

sources to connect to MR.

Corporation

BATT

ON

SWT

MR

PFI

PFO

GND

WDI

LOWLINE

RESET

WDO

UNREGULATED

SUPPLY FAILURE

OTHER SYSTEM

RESET SOURCES

0.47F

ADDRESS

DECODE

0.1

µF

+5V

0.1

µF

CMOS

RAM

AO-A15

µP

I/O

NMI

RESET

INT

UNREGULATED

SUPPLY

MANUAL RESET

OTHER

RESET

SOURCES

*

*

MR

Corporation

MR

RESET

0V

25

µs MIN

7

µs TYP

15

µs TYP