ATA663431_14 Datasheet, PDF (6/32 Pages) ATMEL Corporation – LIN SBC including LIN Transceiver

3.12
NTRIG Input Pin
The NTRIG input pin is the trigger input for the window watchdog. A pull-up resistor is implemented. A falling edge triggers
the watchdog. The trigger signal (low) must exceed a minimum time of t_trigmin to generate a watchdog trigger and avoid false
triggers caused by transients.
3.13
Mode Input Pin (MODE)
Connect the MODE pin directly or via an external resistor to GND for normal watchdog operation. To debug the software of
the connected microcontroller, connect the MODE pin to VCC and the watchdog is switched off. For fail-safe reasons, the
MODE pin has a self-holding function, pulling the input to ground (i.e., watchdog enabled) in case of an open connection.
Note:
If you do not use the watchdog, connect the mode pin directly to VCC.
3.14
Limp Home Watchdog Failure Output (LH)
The LH output pin indicates a failure of the watchdog. It is realized as a high-voltage open drain NMOS structure. During
power up or after a wake-up from sleep mode the LH output is switched off. As the watchdog is only working in normal and
fail-safe mode, the state of the LH output transistor can change only in these two modes. In silent mode the LH output
remains in the same state as it was before switching into silent mode.
If a watchdog reset occurs, the LH output transistor switches on immediately, and it switches off only after three correct
consecutive watchdog trigger pulses have been occurred at the NTRIG pin.
3.15
High-side Switch Pins (HSout, HSin)
This high-side switch is designed for low-power loads such as LEDs, sensors or a voltage divider for measuring the supply
voltage. It is functional in all operating modes of the chip except for sleep mode. Its structure is connected to the VS supply
pin. This pin is short-circuit protected and also protected against overheating, whereas the protective shutdown is
debounced and latched. In other words, after a protective shutdown of the output switch, the control line HSin has to go to
low level first before the output can be restarted again.
The high-side switch is controlled via the low-voltage input pin HSin. If the input is high, the output is switched on. For fail-
safe reasons, the HSin input is equipped with a pull-down resistor to GND. This keeps the high-side switch off in case of a
missing connection from the controller.
Please note that in case of a disconnected system ground, the module can be supplied via the connected load on the high-
side output and an internal ESD structure. This is the case if the load has a different ground connection than the PCB. See
also the “Absolute Maximum Ratings” section for current limits in such cases.
6
ATA663431/ATA663454 [DATASHEET]
9232H–AUTO–09/14