3.0V/3.3V Adjustable Microprocessor

Supervisory Circuits

8

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_______________Detailed Description

General Timing Characteristics

The MAX793/MAX794/MAX795 are designed for 3.3V

and 3V systems, and provide a number of supervisory

functions (see the

Selector Guide on the front page).

Figures 1 and 2 show the typical timing relationships of

the various outputs during power-up and power-down

Manual Reset Input (MAX793/MAX794)

Many microprocessor-based products require manual-

reset capability, allowing the operator, a test technician,

or external logic circuitry to initiate a reset. On the

MAX793/MAX794, a logic low on MR asserts reset. Reset

after it returns high. During the first half of the reset time-

nally forced low to facilitate enabling the battery fresh-

ness seal. MR has an internal 70µA pullup current, so it

can be left open if it is not used. This input can be driven

with TTL- or CMOS-logic levels, or with open-drain/collec-

tor outputs. Connect a normally open momentary switch

from MR to GND to create a manual-reset function; exter-

nal debounce circuitry is not required. If MR is driven

from long cables or the device is used in a noisy environ-

ment, connect a 0.1µF capacitor from MR to ground to

provide additional noise immunity.

Reset Outputs

A microprocessor’s (µP’s) reset input starts the µP in a

known state. These MAX793/MAX794/MAX795 µP

supervisory circuits assert a reset to prevent code exe-

cution errors during power-up, power-down, and

(PFO FOLLOWS PFI)

(MAX793/MAX794)

(MAX793)

PFO

(MAX793/MAX794)

BATT ON

TYPICAL PROPAGATION DELAYS REFLECT A 40mV OVERDRIVE.

5

µs

25

µs

25

µs

25

µs

25

µs