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NE56631-XXD

Active-LOW system reset

Philips Electronics 

Philips Semiconductors

Active-LOW system reset

Product data

NE56631-XX

APPLICATION INFORMATION

VCC

SUPPLY

VCC

RPU

CPU

NE56631-XX VOUT

RESET

VSS

GND

SL01741

Figure 11. Conventional reset application for NE56631-XX.

VCC

SUPPLY

R

D

RPU

CPU

VCC NE56631-XX VOUT

RESET

VSS

GND

SL01742

Figure 12. Power On Reset circuit for NE56631-XX.

The Power ON Reset Circuit shown in Figure 12 is an example of

obtaining a stable reset condition upon power-up. If power supply

rises abruptly, the RESET may go “HIGH” momentarily when VCC is

below the minimum operating voltage (0.85 V). To overcome this

undesirable response, a resistor in placed between positive supply,

VCC and VCC pin and a capacitor from VCC pin to ground. The RC

circuit solution works reasonably well for power-up as long as the

power supply voltage rises faster than the RC time constant. The

RC network provides the necessary reset delay to hold the

microprocessor in reset until its circuitry settles down and normal

operation begins. When the supply turns off, the diode provides a

path for the capacitor to discharge to more quickly assert logic LOW

reset.

2003 Feb 14

8

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