G698 datasheet(7/8 Pages) GMT

7 / 8 page

Ver: 1.3

Jun 03, 2004

TEL: 886-3-5788833

http://www.gmt.com.tw

G698/G699

Global Mixed-mode Technology Inc.

Interfacing to µPs with Bidirectional Reset Pins

Since the RESET output on the G699L is open drain,

this device interfaces easily with µPs that have bidi-

rectional reset pins, such as the Motorola 68HC11.

Connecting the µP supervisor’s RESET output di-

rectly to the microcontroller’s (µC’s) RESET pin with

a single pull-up resistor allows either device to assert

reset (Figure 4).

Figure 4. Interfacing to µPs with Bidirectional Reset

I/O

G699L Open-Drain RESET Output Allows Use with

Multiple Supplies

Generally, the pull-up connected to the G699L will

connect to the supply voltage that is being monitored

at the IC’s VCC pin. However, some systems may use

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

supply to reset circuitry powered by some other supply

(Figure 5). Note that as the G699L’s VCC decreases

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

RESET . Also, with any pull-up, RESET will be pulled

high as VCC decays toward 0. The voltage where this

occurs depends on the pull-up resistor value and the

voltage to which it is connected.

Figure 5. G699L Open-Drain RESET Output Allows

Use with Multiple Supplies

Benefits of Highly Accurate Reset Threshold

Most µP supervisor ICs have reset threshold voltages

between 5% and 10% below the value of nominal

supply voltages. This ensures a reset will not occur

within 5% of the nominal supply, but will occur when

the supply 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 G69_ _463/G69_ _308 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.

RESET

INPUT

GND

µP

RESET

GND

G699

MOTOROLA

68HCXX

RPULL-UP

VCC

RESET

INPUT

GND

µP

RESET

GND

G699

MOTOROLA

68HCXX

RPULL-UP

VCC

RESET

INPUT

GND

5V SYSTEM

RESET

GND

G699

RPULL-UP

+3.3V

+5.0

RESET

INPUT

GND

5V SYSTEM

VCC

RPULL-UP

+3.3V

+5.0V

VCC

RESET

INPUT

GND

5V SYSTEM

RESET

GND

G699

RPULL-UP

+3.3V

+5.0

RESET

INPUT

GND

5V SYSTEM

VCC

RPULL-UP

+3.3V

+5.0V

VCC

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