ADM8693ANZ データシートの表示（PDF） - Analog Devices

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ADM8693ANZ

Microprocessor Supervisory Circuits

Analog Devices 

ADM8690/ADM8691/ADM8692/ADM8693/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

WD I

ADM869x

Figure 28. Programming 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 ADM869x 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.

This can be done 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 time-

out delay of 100 seconds. When the control input is low, the

OSC SEL pin is driven high, selecting the internal oscillator.

The 100 ms or the 1.6 s period is chosen, depending on which

diode is used, as shown in Figure 29. With D1 inserted, the

internal timeout is set at 100 ms; with D2 inserted, the timeout

is set at 1.6 seconds.

CONTROL

INPUT1

D1

OSC SEL

D2

ADM869x

OSC IN

1LOW = INTERNAL TIMEOUT

HIGH = EXTERNAL TIMEOUT

Figure 29. Programming the Watchdog Input

Rev. B | Page 15 of 20

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