Data Sheet

9

Rev. 1.21, 2014-11-19

TLE7273-2

Block Description and Electrical Characteristics

is in the very first turn after power up a long open window with tmax = 4 *

t

corresponds to the standard timing setting as described in the specification.

When a valid trigger signal is detected during the open window a closed window is initialized immediately. A trigger

signal within the closed window is interpreted as a pretrigger failure and results in a reset. After the closed window

the open window with the duration

t

has occurred, at maximum

t

A HIGH to LOW transition of the watchdog trigger signal at pin WDI is considered as a valid trigger pulse.

See Figure 7: To avoid wrong triggering due to parasitic glitches two HIGH samples followed by two LOW samples

(sample period

t

A reset is generated (RO goes LOW) if there is no trigger pulse during the open window or if a pretrigger occurs

during the closed window. The triggering is correct also, if the first three samples (two HIGH one LOW) of the

trigger pulse at pin WDI are inside the closed window and only the fourth sample (the second LOW sample) is

taken in the open window.

After turning OFF the Watchdog by output current reduction, RO remains high. (see also the signal diagram in

Figure 6). After turning ON the WWD again by exceeding the current threshold, the logic cycle starts again with

the Ignore Window and goes then into the “1st. long open window”. This 1st long OW is maximum 4 *

t

allows the re-synchronisation between the micro controller and the WWD timing. The 1st. long OW is closed by

the first valid trigger on WDI from the mirco controller. This trigger ensures the synchronisation. As soon as this

trigger is done, the micro controller timing must be stable and correspondent to

t

Figure 5

Window Watchdog State Diagram, Watchdog and Reset Modes

AEA03527_1.VSD

No Trigger

Closed

Window

Open

Window

Trigger

WM1

LLH

H

WM2

L

H

L

H

Window Watchdog Mode

Fast

Slow

Fast

Off

Reset

Trigger

Ignore

Window

Always

Always

No Trigger During

Open Window

Trigger During

Closed Window

Reset Mode

Fast

Slow

Slow

Slow

Watchdog

OFF

IQ > 5mA

Always

IQ < 0.5mA