TJA1043 INH引脚问题

[GLB]

1043在sleep模式下断开电源，然后只给VBAT供电，这时候INH引脚为低电平。1043在normal模式下断开电源，然后只给VBAT供电，这时候INH引脚电平为高。请问这样的状态对吗？1043在检测到VBAT供电后会首先进入standby模式吗？

[GLB]

As shown in the figure, the green INH pin and the yellow VIO pin. At this point, VBAT has started to supply power. As can be seen from the diagram, the INH pin has been raised before the VIO/VCC connection was made. The INH pin is connected to the ground through a 10K resistor.

[JozefKozon]

Dear Jin,

please share your schematic with voltage levels and part values.

With Best Regards,

Jozef

[JozefKozon]

Dear Jin, 

thank you for additional information. This particular power up behavior is not described in the TJA1043 datasheet, but it is logical to be this way. It is expected that the VIO and VCC will be powered from the VBAT through separate regulators. The regulators are expected to be controlled by the INH pin. If you will connect the battery to the TJA1043, the INH pin should be pulled high to enable the regulators for the VIO and VCC pins. Then if there isn't any problem with the regulators or with the VCC/VIO pins (e.g. short to GND) the VCC and VIO will be powered. If the INH pin would not be pulled high after battery connection, the regulators would not be turned on and the VCC/VIO pins would not be powered, always forcing TJA1043 to sleep mode. The VIO and VCC undervoltage detection time is 100 to 350ms. So after the battery connection the INH will be pulled high and the TJA1043 will check the VCC and VIO for undervoltage.

The VCC and VIO undervoltage recovery time is 1 to 5ms. In your case it looks to be 1ms from INH high to VIO powered, which is within the boundaries. 

With Best Regards,

Jozef

[GLB]

1、However, when entering the sleep mode and then losing power, and then connecting to VBAT, at this point INH remains at a low level. 2、In the normal mode, power is cut off and then VBAT is powered on. At this point, INH will perform a pull-up operation. Why are there these two situations?

[JozefKozon · Accepted solution]

Dear Jin,

Situation 1

Sequence:

1. TJA1043 enters Sleep Mode

2. Power is lost on VCC / VIO

3. Battery (VBAT) is later re‑connected

4. INH stays LOW

When the TJA1043 is in Sleep Mode, the INH output is defined to be:

• High‑impedance / floating → external regulator is OFF → INH appears LOW

When power is lost and returns, the TJA1043 interprets this as:

• VBAT undervoltage event → device enters Forced Standby Mode

• In Forced Standby Mode, INH = HIGH ONLY IF VBAT has recovered and the wake‑up flags have been handled

Coming from Sleep Mode, the device does NOT automatically re‑enable INH.

INH will only go HIGH when the device is commanded to wake up

(through STBN or a wake‑up event).

Until that happens:

• The device remains in Sleep / Forced Sleep state

• INH = floating → external regulator OFF → INH reads LOW

This is intentional fail‑safe behavior, preventing a random wake-up after power glitches.

Situation 2

Sequence:

1. TJA1043 is in Normal Mode
2. Power is cut off (VCC/VIO drop)
3. VBAT is re‑applied
4. INH pulls HIGH

When the device was previously in Normal Mode, its last known state was:

• INH = HIGH (normal mode activates external regulators)

When power returns:

• The TJA1043 performs a power‑on sequence
• VBAT recovery triggers:
  • PWON flag
  • Wakeup flag
  • Wakeup source flag

 INH is immediately driven HIGH again to restart the ECU’s regulators

This is required behavior because in Normal Mode, the ECU must restart normally after a battery reconnection.

 With Best Regards,

Jozef

[GLB]

Thank you very much！

[GLB]

When 1043 is powered off in normal mode and then supplied with power from VBAT, INH will be pulled high for a period of time and then pulled low. Again, disconnect the VBAT, and continue to supply power to the VBAT. At this point, the INH pin will remain at a low level.

[JozefKozon]

Dear Jin,

When the 1043 is in sleep mode with the power supply disconnected and only VBAT is powered, the INH pin is low.

[A] Yes, correct. INH is floating. 

When the 1043 is in normal mode with the power supply disconnected and only VBAT is powered, the INH pin is high. Is this configuration correct?

[A] Incorrect. The TJA1043 need to have the VCC and VIO powered. If VCC or VIO undervoltage is detected, the TJA1043 will transfer to sleep mode. 

After detecting VBAT power, will the 1043 first enter standby mode?

[A] Depending if also VIO and VCC are powered. If yes, the TJA1043 will transfer to the mode indicated by the STB_N and EN pins level. If either VIO or VCC are not powered, then after the TJA1043 VBAT will be powered, the TJA1043 will transfer to sleep mode. 

With Best Regards,

Jozef