ADM8690AN 데이터 시트보기 (PDF) - Analog Devices

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ADM8690AN

Microprocessor Supervisory Circuits

Analog Devices 

ADM8690/ADM8691/ADM8695

ALTERNATE WATCHDOG INPUT DRIVE CIRCUITS

The watchdog feature can be enabled and disabled under

program control by driving WDI with a three-state buffer (see

Figure 28). When three-stated, the WDI input floats, thereby

disabling the watchdog timer.

WATCHDOG

STROBE

CONTROL

INPUT

WDI ADM8690/

ADM8691/

ADM8695

Figure 28. Enabling and Disabling the Watchdog Input

This circuit is not entirely foolproof, and it is possible for a

software fault to erroneously three-state the buffer, preventing

the ADM8690/ADM8691/ADM8695 from detecting that the

microprocessor is no longer operating correctly. In most cases,

a better method is to extend the watchdog period rather than

disable the watchdog.

Data Sheet

For the ADM8691/ADM8695, the watchdog period can be

extended under program control using the circuit shown in

Figure 29. When the control input is high, the OSC SEL pin is

low and the watchdog timeout is set by the external capacitor.

A 0.01 μF capacitor sets a watchdog timeout delay of 100 sec.

When the control input is low, the OSC SEL pin is driven high,

selecting the internal oscillator. The 100 ms or the 1.6 sec

period is chosen, depending on which diode is used, as shown

in Figure 29. With D1 inserted, the internal timeout is set to

100 ms; with D2 inserted, the timeout is set to 1.6 sec.

CONTROL

INPUT1

D1

OSC SEL

D2

ADM8691/

ADM8695

OSC IN

1LOW = INTERNAL TIMEOUT

HIGH = EXTERNAL TIMEOUT

Figure 29. Extending the Watchdog Period

Rev. C | Page 16 of 24

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