18.2.5 Fail-safe Mode

The device automatically switches to Fail-Safe mode at system power-up or after a wake-up event. The LIN_INH output is switched on and the LIN transceiver is switched off. The IC stays in this mode until LIN_EN is switched to high. The IC then changes to Normal mode. During Fail-Safe mode, the LIN_TXD pin is an output, and together with the LIN_RXD output pin, signals the fail-safe source.

If the device enters Fail-Safe mode coming from the Normal mode (LIN_EN = 1) due to a VS undervoltage condition (VVS < VVS_th_N_F_down), it is possible to switch into Sleep mode by a falling edge at the LIN_EN input. With this feature, the current consumption is further reduced.

A wake-up event from Sleep mode is signaled to the microcontroller using the LIN_RXD pin and the LIN_TXD pin. A VS undervoltage condition is also signaled at these two pins. The coding is shown in Table 18-2.

Table 18-2. Signaling In Fail-Safe Mode
Fail-Safe SourcesLIN_TXD(1)LIN_RXD
LIN Wake-up (LIN_BUS pin)

Low

Low

Local Wake-up (LIN_WKIN pin)

Low

High

VSth (battery) Undervoltage Detection, VS < 3.9V

High

Low

Note:
  1. Assuming an external pull-up resistor (typically 5 kW) has been added on pin LIN_TXD to the power supply of the microcontroller. Wake-up Scenarios from Sleep Mode.