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 MAX810 if RESET is required to remain valid for

Interfacing to µPs with

Bidirectional Reset Pins

Since the RESET output on the MAX803 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

pull-up resistor allows either device to assert reset

(Figure 3).

MAX803 Open-Drain RESET Output

Allows Use with Multiple Supplies

Generally, the pull-up connected to the MAX803 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 pull-up, RESET will be pulled

occurs 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%,

this leaves a zone of uncertainty where the supply is

between 5% and 10% low, and where the reset may or

may not be asserted.

The MAX8_ _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.

3-Pin Microprocessor Reset Circuits

6

_______________________________________________________________________________________

RESET

GND

RESET

INPUT

MAX803

5V SYSTEM

GND

+3.3V

+5.0V

Figure 4. MAX803 Open-Drain RESET Output Allows Use with

Multiple Supplies

RESET

GND

RESET

INPUT

MAX803

MOTOROLA

68HCXX

µP

GND

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

TRANSISTOR COUNT: 275 (SOT23)

380 (SC70)

___________________Chip Information