µP Supervisory Circuits with Windowed

(Min/Max) Watchdog and Manual Reset

6

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Detailed Description

The MAX6323/MAX6324 µP supervisory circuits main-

tain system integrity by alerting the µP to fault condi-

power-on reset, brownout detect, and power-down

reset), the devices include a sophisticated watchdog

timer that detects when the processor is running out-

side an expected window of operation for a specific

application. The watchdog signals a fault when the

input pulses arrive too early (faster than the selected

lead to poor or dangerous system performance in tight-

ly controlled operating environments. Incorrect timing

could be the result of improper µP clocking or code

execution errors. If a timing error occurs, the

MAX6323/MAX6324 issue a watchdog pulse output,

independent from the reset output, indicating that sys-

tem maintenance may be required.

Watchdog Function

A pulse on the watchdog output WDPO can be trig-

gered by a fast fault or a slow fault. If the watchdog

input (WDI) has two falling edges too close to each

pulsed low. Normal watchdog operation is displayed in

Figure 4 (WDPO is not asserted). The internal watch-

dog timer is cleared when a WDI falling edge is detect-

ed within the valid watchdog window or when the

device’s RESET or WDPO outputs are deasserted. All

WDI input pulses are ignored while either RESET or

WDPO is asserted. Figure 1 identifies the input timing

regions where WDPO fault outputs will be observed

deasserts, the first WDI falling edge is ignored for the

fast fault condition (Figure 2).

Upon detecting a watchdog fault, the WDPO output will

pulse low for 1ms. WDPO is an open-drain output.

Connect a pullup resistor on WDPO to any supply up to

+6V.

reset monitor to ensure that the µP is started in a known

state and to prevent code execution errors during

power-up, power-down, or brownout conditions.

*UNDETERMINED STATES MAY OR MAY NOT GENERATE A FAULT CONDITION.

POSSIBLE STATES

GUARANTEED TO

ASSERT WDPO

GUARANTEED TO

ASSERT WDPO

GUARANTEED NOT TO

ASSERT WDPO

FAST FAULT

CONDITION 1

SLOW FAULT

CONDITION 3

NORMAL OPERATION

CONDITION 2

)

*UNDETERMINED

*UNDETERMINED

Figure 1. Detailed Watchdog Input Timing Relationship