NE56604-42D データシートの表示（PDF） - Philips Electronics

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NE56604-42D

System reset with built-in Watchdog timer

Philips Electronics 

Philips Semiconductors

System reset with built-in Watchdog timer

Product data

NE56604-42

TECHNICAL DESCRIPTION

General discussion

The NE56604-42 combines a Watchdog timer and an undervoltage

reset function in a single SO8 surface mount package. This provides

a space-saving solution for maintaining proper operation of typical

5.0 volt microprocessor-based logic systems. Either function, or

both, can force the microprocessor into a reset.

While the Watchdog monitors the microprocessor operation, the

undervoltage reset monitors the supply voltage to the

microprocessor. If the microprocessor clock signal ceases or

becomes erratic, the NE56604-42 outputs a reset signal to the

microprocessor. If the microprocessor supply voltage sags to

4.2 volts or less, the NE56604-42 outputs a reset signal for the

duration of the supply voltage deficiency. The undervoltage reset

signal allows the microprocessor to shut down in an orderly manner

to avoid system corruption. In addition to a single reset output, the

NE56604-42 has complementary RESET and RESET outputs for

system use. The undervoltage detection threshold incorporates

hysteresis to prevent generating erratic resets.

VCC

5

RCT

6 RCT

The Watchdog timer requires a pulse input. Normally this signal

comes from the system microprocessor’s clock. For operation, an

external resistor (RCT) must be connected from Pin 6 to VCC and an

external capacitor (CT) from Pin 1 to ground. Normally a 0.1 µF

capacitor is used for CT. The external RCT resistor and CT capacitor

establish the required minimum frequency of Watchdog input signal

for the device to not output a reset signal. The RCT resistor

establishes, in part, the rate of charge of the CT capacitor. In the

absence of a Watchdog input pulse, the CT capacitor charges to the

0.2 volt threshold of the internal comparator, causing a reset signal

to be output. If microprocessor clock signals are received within the

required interval, no Watchdog reset signal will be output. The

Watchdog function can be disabled by grounding Pin 6 without

affecting the undervoltage detection function.

Although the temperature coefficient of detection threshold is

specified over a temperature of –20 °C to +70 °C, the device will

support operation in excess of this temperature range. See the

supporting curves for performance over the full temperature range of

–40 °C to +85 °C. Some degradation in performance will be

experienced at the temperature extremes and the system designer

should take this into account.

R

54 kΩ

R

58 kΩ

7

R

C

26 kΩ

3

PULSE

GENERATOR

0.1 V

1.2 µA

SQ

R

R

R

0.2 V

SQ

R

SQ

R

R

47 kΩ

12 µA

R

R

1 CT

4 GND

Figure 19. Functional diagram.

2

RESET

8

RESET

SL01310

2003 Oct 15

9

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