TH8065 Datasheet, PDF (23/40 Pages) Melexis Microelectronic Systems – Voltage Regulator with LIN Transceiver and Watchdog

TH8065
Voltage Regulator with LIN Transceiver and Watchdog
WDI
CWD
VCWDH
VCWDM
VCWDL
RESET
t_{WDt_R}
WDI = High or Low
t_{WD_per}
t_{WD_R}
Figure 14 - Watchdog timing
The reset output will be switched from high to low (watchdog reset), if the voltage on pin CWD reaches
V_CWDL. The reset output stays at low level until the voltage at C_WD has reached the level of V_CWDH.
The RESET pin generates a periodic signal with low pulse width of t_{WD_R} and a period of t_{WD_per}, if no
retrigger of WDI takes place.
Calculation of Watchdog time
Watchdog reset time:
( ) _{tWD _ R =}
V_CWDH − V_CWDL
I _{CWD _ pu}
∗ C_WD
Max. watchdog reset trigger time
( ) _{tWDt _ R =}
V_CWDH − V_CWDL
I_{CWD _ pd}
∗ C_WD
C_WD Watchdog capacity connected to pin CWD
V_CWDH Upper watchdog threshold
V_CWDL Lower watchdog threshold
I_{CWD_pu} CWD charge current
I_{CWD_pd} CWD discharge current
With the valid charge and discharge currents of C_WD of the TH8065 is a simple calculation of the capacity
values for a defined watchdog trigger time and reset time possible:
[ ] [ ] t_{WDt _ R} ms = C_WD nF
t_{WD _ R} [ms] = 0.1∗ C_WD[nF ]
Example:
C_WD = 10nF → t_{WDt _ R} = 10ms and t_{WD _ R} = 1ms
Within a timeframe of 10ms the MCU has to reset the watchdog to prevent a reset generation. The
complete watchdog period t_{WD_per} = 11ms.
If the watchdog has to be deactivated for e.g. firmware development, the pin CWD has to be directly
connected to GND. The reset signal is in this case only determined by the reset thresholds.
TH8065 – Datasheet
3901008065
Page 23 of 40
May 2006
Rev 003