Datasheet

TLE 4471
Data Sheet 19 Rev. 1.6, 2009-02-03
Watchdog
The reset and watchdog timing can be defined independently of each other by two delay
capacitors
C
DR
and C
DW
at pins DR and DW.
The watchdog function supervises the microcontroller including time base failures. If
there is no positive edge within a certain pulse repetition time
t
wp
or the trigger pulse is
too short a reset is generated. Programming of the max. repetition time is done by a
delay capacitor
C
DW
at pin DW.
The frequency of the watchdog pulses generated by the microcontroller has to be higher
than the minimum pulse sequence
t
wp
set by the external reset delay capacitor C
DW
. The
pulse repetition time can be calculated as follows:
(4)
Figure 7 Watchdog Timing
If the watchdog is not used in an application the pin WD has to be connected to GND.
t
wp
C
DW
V
DW dt,
V
DW st,
–
I
DW ch,
--------------------------------------
×=
AET03000
V
I
t
t
V
Q1
V
W
t
t
V
DW
V
DR
t
t
V
R
t
>
10 µs
t
25 µs
t
WP
V
DW,dt
V
DW,st
V
DR,dt
V
DR,st
t
dr
t
rr
Missing edge
at Watchdog
Watchdog pulses
too short
>