MCP2050 datasheet(6/40 Pages) MICROCHIP

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MCP2050

DS20002299C-page 6

 2012-2014 Microchip Technology Inc.

1.2.2

WINDOWED WATCHDOG

BEHAVIOR

After windowed watchdog begins its normal behavior,

three different cases can appear.

• A pulse (falling edge) on the WWDTTRIG pin is

detected within the trigger window; the watchdog

timer will be reset, and a new watchdog period will

begin;WWDTRESETpinremainshigh(Figure 1-3.)

• A pulse (falling edge) on the WWDTTRIG pin is

detected before the trigger window (too early trig-

ger); WWDTRESET is asserted (low) immediately

after the falling edge is detected for approximately

tWDRST; the counter is reset and the next watchdog

period begins at the rising edge of the voltage on

WWDTRESET pin (Figure 1-12).

• No pulse on the WWDTTRIG pin is detected

during the whole watchdog window (no trigger);

WWDTRESET is asserted (low) for approximately

tWDRST when the timer has expired; the counter is

reset and the next watchdog period begins at the

rising edge of the voltage on WWDTRESET pin

(Figure 1-5).

The trigger window is between 50% to 100% of the

watchdog window length, tWLENGTH. The window

length is determined by the external resistor between

WWDTSELECT pin and VSS.

EQUATION 1-1:

tWDRST = 150 μs typical

RWWDTSELECT is in kΩ; its value ranges from 33 kΩ to

680 kΩ and window length ranges from 7 ms to 120 ms

typical.

If the WWDTSELECT pin is floating, the watchdog is

disabled and the WWDTRESET remains high.

FIGURE 1-3:

CORRECT TRIGGER

tWLENGTH = (0.175 ms × RWWDTSELECT) + 1.2 typical

Too early

Trigger window

Window length

50%

Earliest trigger point

Lastest trigger point

Next period

Too early

Trigger window

Window length

50%

New period begins

WWDTTRIG

WWDTRESET

TWD

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