Window Frame to Reset the WDI

Detection of

Rising Edge

WDI

t

11

TPS3813J25, TPS3813L30, TPS3813K33, TPS3813I50

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SLVS331H – DECEMBER 2000 – REVISED JULY 2016

Product Folder Links: TPS3813J25 TPS3813L30 TPS3813K33 TPS3813I50

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8.5 Programming

8.5.1 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

Table 2.

Table 2. Cap-Free Timer Settings

SELECTED OPERATION MODE

WINDOW FRAME

LOWER WINDOW FRAME

WDT = 0 V

WDR = 0 V

Max = 0.3 s

Max = 9.46 ms

Typ = 0.25 s

Typ = 7.86 ms

Min = 0.2 s

Min = 6.27 ms

Max = 0.3 s

Max = 2.43 ms

Typ = 0.25 s

Typ = 2 ms

Min = 0.2 s

Min = 1.58 ms

WDR = 0 V

Max = 3 s

Max = 93.8 ms

Typ = 2.5 s

Typ = 78.2 ms

Min = 2 s

Min = 62.5 ms

Max = 3 s

Max = 23.5 ms

Typ = 2.5 s

Typ = 19.6 ms

Min = 2 s

Min = 15.6 ms

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

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

In the shaded area of Figure 7, it cannot be predicted if the device detects a violation or not and release a reset.

Figure 7. Upper and Lower Boundary Visualization

8.5.2 Programmable Window-Watchdog by Using an External Capacitor

The upper boundary of the watchdog timer can be set by an external capacitor connected between the WDT pin

and GND. Common consumer electronic capacitors can be used to implement this feature. They must have low

ESR and low tolerances because the tolerances have to be considered if the calculations are performed. The

first formula is used to calculate the upper window frame. After calculating the upper window frame, the lower

The trigger pulse has to fit into this window frame.

The external capacitor must have a value between a minimum of 155 pF and a maximum of 63 nF.