7.3.2.1 Timing Rules of Window-Watchdog

After the reset of the supervisor is released, the lower boundary of the first WDI window is disabled. However,

after the first WDI pulse low-to-high transition is detected, the lower boundary function of the window is enabled.

All further WDI pulses must fit into the configured window frame.

The lower boundary of the watchdog window begins with the rising edge of the WDI trigger pulse. At the same

time, all internal timers are reset. If an external capacitor is used, the lower boundary is impacted because of

the different oscillator frequency. See the Section 8.2.2.1 section for additional details. Figure 7-3, especially the

shaded boundary area, was prepared in a nonreal ratio scale to better visualize the description.

VDD

td

td

td

VIT

1.1 V

RESET

Output Condition

Undefined

WDI

1st Window

Without Lower

Boundary

2nd Window

With Lower

Boundary

3rd Window

With Lower

Boundary

Trigger Pulse

Lower Window

Boundary

1st Window

Without Lower

Boundary

1st Window

Without Lower

Boundary

2nd Window

With Lower

Boundary

3rd Window

With Lower

Boundary

t

t

t

Output Condition

Undefined

Figure 7-3. Timing Diagram

7.3.3 Watchdog Software Considerations

To benefit from the window watchdog feature and help the watchdog timer monitor the software execution more

closely, TI recommends that the watchdog be set and reset at different points in the program rather than pulsing

the watchdog input periodically by using the prescaler of a microcontroller or DSP. Furthermore, the watchdog

trigger pulses should be set to different timings inside the window frame to release a defined reset if the program

should hang in any subroutine. This setting allows the window watchdog to detect timeouts of the trigger pulse

as well as pulses that distort the lower boundary.

7.4 Device Functional Modes

The functional mode for the TPS3813-Q1 family family of devices is either on or reset. Table 7-2 lists the device

truth table.

Table 7-2. Device States

CONDITION

STATE

RESET

VDD > VIT

On

H

VDD < VIT

Reset

L

Watchdog fault

TPS3813K33-Q1, TPS3813I50-Q1

SPRS288H – MAY 2008 – REVISED OCTOBER 2021

www.ti.com

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