TJA1043 power on

[810656514]

Hello dear NXP community,
Use three constant current sources to provide voltage to TJA1043, VBAT voltage 10V, VCC voltage 5V, VIO voltage 3V. The wake pin, STB_N pin, and EN pin are all floating. After power-on, TJA1043 is found to be in sleep mode. I would like to ask what working mode should TJA1043 enter after power-on?
Will the wake-up signal of the wake pin be detected in listen-only mode?
Let the VBAT voltage be 10V and adjust the VCC voltage to be lower than 3.5V. The test found that the TJA1043 did not enter the sleep mode, and if the VIO voltage was adjusted to be lower than 1.8V, the TJA1043 entered the sleep mode.
But according to the data sheet, “UVNOM is the VCC and VIO undervoltage detection flag. The flag is set when the voltage on pin VCC drops below the VCC undervoltage detection voltage, Vuvd(VCC), for longer than the
undervoltage detection time, tdet(uv), or when the voltage on pin VIO drops below Vuvd(VIO)
for longer than tdet(uv). When the UVNOM flag is set, the transceiver enters Sleep mode to
save power and to ensure the bus is not disturbed. In Sleep mode the voltage regulators
connected to pin INH are disabled, avoiding any extra power consumption that might be
generated as a result of a short-circuit condition.”

thank you.

Regards,

Chandan

[TomasVaverka]

Hello Chandan,

The TJA1043 provides five different operating modes, which are controlled by the input pins STB_N and EN. The reference state diagram for the operating modes can be found in the data sheet (Fig. 4).

If STB_EN and EN pins are left floating, the device powers on to Standby mode.

In the case of an undervoltage condition on the pin VCC or VIO, the TJA1043 is forced into Sleep Mode by setting the internal undervoltage detection flag UVNOM, overruling the current mode selection at the pins STB_N and EN. As a result, pin INH becomes floating (high impedance state), disabling the voltage regulator.

For more information, please refer to the AH1014 (Chapter 6.8 - Undervoltage detection & recovery).

Best regards,

Tomas