TH8065 Datasheet, PDF (21/40 Pages) Melexis Microelectronic Systems – Voltage Regulator with LIN Transceiver and Watchdog

TH8065
Voltage Regulator with LIN Transceiver and Watchdog
3.8 RESET and Watchdog
The TH8065 contains a combined reset- and watchdog-unit which secures the correct initialization and
generation of the reset signal.
VSUP,
VCC
V_RES
int.
POR
signal
t_Res
RESET
Start-up
WDI
ON delay
CWD VCWDH
VCWDL
Watchdog
t_WDL
t_WDH
t_rr
Power-off
Figure 11 - Reset and Watchdog behaviour
The RESET pin outputs the reset state and the watchdog state of the TH8065. The POR timer will be started
if V_SUP is switched on and V_CC> POR threshold (4.65V). The Watchdog is inactive. After the time t_Res the
RESET output is switched from low to high and the watchdog becomes active. The charging of the watchdog
capacity starts and dependent from the trigger pulse on the WDI input the Reset outputs the status of the
watchdog.
The watchdog is only active if V_CC > V_RES. If V_CC drops below V_RES the watchdog will be switched off and the
watchdog capacity will be discharged.
3.8.1. RESET
The RESET unit combines a VCC low voltage detection unit with fixed POR timer This output is switched
from low to high if V_SUP is switched on and V_CC>V_RES (4.65V) after the time t_Res .
All conditions which cause a drop of the V_CC voltage will be detected from the low voltage reset unit which
generates a reset signal. The TH8065 will be reinitialized if the V_CC voltage rises above the low voltage limit.
If the voltage V_CC drops below V_RES then the RESET output is switched from high to low after the time t_rr has been
reached. For this reason short breaks of the V_CC voltage and uncontrolled reset generations will be inhibited.
The circuitry of the RESET output driver guarantees, that the reset low level during decreasing of the V_CC
voltage will be secure kept (see Figure 13).
TH8065 – Datasheet
3901008065
Page 21 of 40
May 2006
Rev 003