TLE9263QX datasheet(103/164 Pages) INFINEON

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Data Sheet

103

Rev. 1.1, 2014-09-26

TLE9263QX

Supervision Functions

15.2.2

Window Watchdog

Compared to the time-out watchdog the characteristic of the window watchdog is that the watchdog timer period

is divided between an closed and an open window. The watchdog must be triggered within the open window.

A correct watchdog trigger results in starting the window watchdog period by a closed window followed by an open

window.

The watchdog timer period is at the same time the typical trigger time and defines the middle of the open window.

Taking the oscillator tolerances into account leads to a safe trigger area of:

tWD x 0.72 < safe trigger area < tWD x 1.20.

The typical closed window is defined to a width of 60% of the selected window watchdog timer period. Taking the

tolerances of the internal oscillator into account leads to the timings as defined in Figure 50.

A correct watchdog service immediately results in starting the next closed window.

Should the trigger signal meet the closed window or should the watchdog timer period elapse, then a watchdog

reset is created by setting the reset output RO low and the SBC switches to SBC Restart or SBC Fail-Safe Mode.

Figure 50

Window Watchdog Definitions

15.2.3

Watchdog Setting Check Sum

A check sum bit is part of the SPI commend to trigger the watchdog and to set the watchdog setting.

The sum of the 8 data bits in the register WWD_CTRL needs to have even parity (see Equation (3)). This is

realized by either setting the bit CHECKSUM to 0 or 1. If the check sum is wrong, then the SPI command is

ignored, i.e. the watchdog is not triggered or the settings are not changed and the bit SPI_FAIL is set.

The checksum is calculated by taking all 8 data bits into account. The written value of the reserved bit 3 of the

WWD_CTRL register is considered (even if read as ‘0’ in the SPI output) for checksum calculation, i.e. if a 1 is

written on the reserved bit position, then a 1 will be used in the checksum calculation.

(3)

closed window

open window

t / [tWD_TIMER]

safe trigger area

tWD x 0.72

tWD x 1.20

uncertainty

tWD x 0.48

tWD x 1.80

Watchdog Timer Period (WD_TIMER)

Typ. closed window

Typ. open window

tWD x 0.6

tWD x 1.0

tWD x 0.9

CHKSUM

Bit15

…

Bit8

⊕⊕

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