3-Pin, Low-Power

µP Reset Circuits

4

_______________________________________________________________________________________

GND

MAX6802

RESET

GND

RESET

MOTOROLA

68HCXX

µP

100k

Ω

Applications Information

Interfacing to µPs with Bidirectional

Reset Pins

Since the RESET output on the MAX6802 is open-drain,

this device interfaces easily with µPs that have bidirec-

tional reset pins, such as the Motorola 68HC11.

Connecting the µP supervisor’s RESET output directly

to the microcontroller’s (µC’s) RESET pin with a single

pullup resistor allows either device to assert reset

(Figure 1).

In addition to issuing a reset to the µP during power-up,

power-down, and brownout conditions, these devices are

transients (glitches). The Typical Operating Characteristics

show the Maximum Transient Duration vs. Reset

Comparator Overdrive graph. The graph shows the maxi-

typically have without issuing a reset signal. As the ampli-

tude of the transient increases, the maximum allowable

pulse width decreases.

Figure 1. Interfacing to µPs with Bidirectional Reset Pins

TOP VIEW

1

2

RESET (RESET)

MAX6800

MAX6801

MAX6802

SOT23-3

( ) ARE FOR MAX6800

GND

Pin Configuration

GND

MAX6801

RESET

100k

Ω

(a)

GND

MAX6800

RESET

100k

Ω*

(b)

*ASSUMES HIGH-Z RESET INPUT TO THE

µP

MAX6801

RESET

RESET

GND

GND

µP

Typical Operating Circuit