TLE4471 Datasheet, PDF (22/26 Pages) Infineon Technologies AG – Triple Voltage Regulator

TLE 4471
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 triggerpulse 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:
t_wp=
C_D
W
⋅
V_{-----D---W-----,-d---t--}–_-----V_{----D----W----,-s--t}
I _{D W ,c h}
V_I
t
V_Q1
t
t ^> 10 µs
t ^> 25 µs
V_W
V_DW
V_DR
V_R
t_WP
t_dr
t
V_DW,dt
V_DW,st
t
V_DR,dt
V_DR,st
t_rr
t
Missing edge
at Watchdog
Watchdog pulses
too short
t
AET03000
Figure 7 Watchdog Timing
If the watchdog is not used in an application the pin WD has to be connected to GND.
Data Sheet Rev. 1.1
22
2001-09-06