maximum allowable pulse width decreases. Typically, for

goes 100mV below the reset threshold and lasts 20µs or

less will not cause a reset pulse. A 0.1µF bypass capaci-

additional transient immunity.

Ensuring a Valid Reset Output

no longer sinks current—it becomes an open circuit.

Therefore, high-impedance CMOS-logic inputs con-

nected to RESET can drift to undetermined voltages.

This presents no problem in most applications since

below 1V. However, in applications where RESET must

be valid down to 0, adding a pull-down resistor to

RESET causes any stray leakage currents to flow to

ground, holding RESET low (Figure 2). R1’s value is not

critical; 100k

Ω is large enough not to load RESET and

small enough to pull RESET to ground.

A 100k

for the MAX6712 if RESET is required to remain valid for

Interfacing to µPs with

Bidirectional Reset Pins

Since the RESET output on the MAX6713 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 µP’s RESET pin with a single pull-up resistor

allows either device to assert reset (Figure 3).

MAX6713 Open-Drain

RESET Output

Allows Use with Multiple Supplies

Generally, the pull-up connected to the MAX6713 will

connect to the supply voltage that is being monitored at

open-drain output to level-shift from the monitored sup-

ply to reset circuitry powered by some other supply

below 1V, so does the IC’s ability to sink current at

RESET. Also, with any pullup, RESET will be pulled high

depends on the pull-up resistor value and the voltage

to which it is connected.

Benefits of Highly Accurate

Reset Threshold

Most µP supervisor ICs have reset threshold voltages

between 5% and 10% below the value of nominal sup-

ply voltages. This ensures a reset will not occur within

5% of the nominal supply, but will occur when the sup-

ply is 10% below nominal.

When using ICs rated at only the nominal supply ±5%,

a zone of uncertainty where the supply is between 5%

and 10% low, and where the reset may or may not be

asserted is left.

The MAX671_L/T/Z use highly accurate circuitry to

ensure that reset is asserted close to the 5% limit, and

long before the supply has declined to 10% below

nominal.

4-Pin SC70 Microprocessor Reset Circuits

with Manual Reset Input

6

_______________________________________________________________________________________

RESET

GND

RESET

INPUT

MAX6713

5V SYSTEM

GND

+3.3V

+5.0V

Figure 4. MAX6713 Open-Drain RESET Output Allows Use with

Multiple Supplies

RESET

GND

MR

RESET

INPUT

MAX6713

MOTOROLA

68HCXX

µP

GND

Figure 3. Interfacing to µPs with Bidirectional Reset I/O

TRANSISTOR COUNT: 380

___________________Chip Information