7.5 Programming

7.5.1 Implementing Window-Watchdog Settings

There are two ways to configure the watchdog timer window the most flexible is to connect a capacitor to WDT

to set the upper boundary of the window watchdog while connecting WDR to either VDD or GND, thus setting the

lower boundary. The other way to configure the timing is by wiring the WDT and WDR pin to either VDD or GND.

By hard-wiring the pins to either VDD or GND there are four different timings available; these settings are listed in

Table 7-2.

Table 7-2. Cap-Free Timer Settings

SELECTED OPERATION MODE

WINDOW FRAME

LOWER WINDOW FRAME

WDT = 0V

WDR = 0V

Max = 0.3s

Max = 9.46ms

Typ = 0.25s

Typ = 7.86ms

Min = 0.2s

Min = 6.27ms

WDR = VDD

Max = 0.3s

Max = 2.43ms

Typ = 0.25s

Typ = 2ms

Min = 0.2s

Min = 1.58ms

WDT = VDD

WDR = 0V

Max = 3s

Max = 93.8ms

Typ = 2.5s

Typ = 78.2ms

Min = 2s

Min = 62.5ms

WDR = VDD

Max = 3s

Max = 23.5ms

Typ = 2.5s

Typ = 19.6ms

Min = 2s

Min = 15.6ms

To visualize the values named in the table, a timing diagram was prepared. It is used to describe the upper and

lower boundary settings. For an application, the important boundaries are the tboundary,max and twindow,min. Within

these values, the watchdog timer must be retriggered to avoid a time-out condition or a boundary violation in

the event of a trigger pulse in the lower boundary. The values in the table above are typical and worst-case

conditions and are valid over the whole temperature range of –40°C to +85°C.

The shaded areas shown in Figure 7-2 are cases where undefined operation can happen. This device can not

detect a violation if a WDI pulse occurs within these three shaded areas. The first shaded area addresses the

situation of two consecutive rising edges occur within a quick amount of time. The typical time between rising

edges must be more than 500µs. The second and third shaded areas are defined by the min and max variance

of the lower boundary (tboundary) and upper boundary ( twindow). Set the WDI rising edge within the tboundary,max

and twindow,min for correct operation.

Window Frame to Reset the WDI

Detection of

Rising Edge

WDI

twindow,min

twindow,typ

twindow,max

boundary,min

t

tboundary,max

tboundary,typ

t

Figure 7-2. Upper and Lower Boundary Visualization

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TPS3813

SLVS331J – DECEMBER 2000 – REVISED AUGUST 2024

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