ADM709

REV. 0

–3–

RESET

at Voltages < 1 V

The ADM709 RESET output is guaranteed to operate with

supply voltages as low as 1 V. If it is desired that the RESET

output remains low below 1 V, then a pull-down resistor should

be connected between the RESET output and GND. A resistor

of 100 k

Ω is suitable. This is illustrated in Figure 5.

R1

RESET

ADM709

GND

Glitch Immunity

The ADM709 is immune to short transients which may occur

generated as a result of minor glitches on the power supply.

Additional glitch immunity may be obtained by connecting a

capacitor (0.1

µF or greater) as close as possible to the V

on the device.

Microprocessors with Bidirectional I-O

Some microprocessors or microcontrollers such as the

MC68HC11 have bidirectional reset lines. In order to avoid

signal contention, a resistor of 4.7 k

Ω should be connected

between the ADM709 RESET output and the microcontroller

RESET

line. This arrangement is shown in Figure 6.

RESET

ADM709

GND

GND

µP

BUFFERED

RESET

+5V

RESET

Figure 6. Interfacing to Microprocessors with

Bidirectional RESET

RESET

ADM709

RESET

GENERATOR

GND

Figure 1. Functional Block Diagram

RESET

ADM709

GND

GND

µP

RESET

Figure 2. Typical Operating Circuit

CIRCUIT INFORMATION

RESET

Output

RESET

is an active low output which provides a reset signal to

the reset threshold. An internal timer holds RESET low for

is intended as a power-on reset signal for the processor. It allows

time for the power supply and microprocessor to stabilize after

power up. Similarly a power supply brownout will initiate a pro-

cessor reset. On power-down, the RESET output remains low

held in a stable shutdown condition as the power supply drops.

VRT

VRT

RESET

Figure 3. Power Off/On RESET Timing

RESET

400ms/DIV