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TCAN1043A-Q1: INH Pin Handling

Shyamasundar Hegde
Prodigy 30 points
Part Number: TCAN1043A-Q1

Tool/software:

Hello Team,

We are using TCAN1043A-Q1 in our instrumentation cluster product.  Using INH pin to enable the regulators on the board. Below is the schematics

Issue what we are facing is when the TRM30 (12V Battery) is connected to our Board very first time, Immediately INH is going HIGH  which is as expected per datasheet  making the product ON.

This we would like to avoid since this will create Board ON issue in vehicle assembly. So we tried making VCC(5V), VIO(3.3V) zero as suggested in datasheet to have undervoltage condition so that INH will be low.

But what we observed is INH is still continuously HIGH even after making VCC (5V), VIO (3.3V) zero .  Below is the picture in the datasheet & we used same concept.

Question is --> We can see from the diagram that After INH goes HIGH only regulators will be turned ON.   Then how it is monitoring VIO, VCC to achieve sleep mode ? Means INH we will set HIGH always irrespective of VCC, VIO right? Because VCC, VIO will be generated after INH enable. 

Is there any other method to make INH low ?  You can suggest some circuit.  (From SW we tried making STB =LOW, EN = HIGH , This is making INH to go low perfectly) 

Is there any IC with TI which gives INH "LOW"  when VBAT is applied first time ? 

Waiting for your valuable feedback. 

Regards,

Shyamasundar Hegde

  • 0
    Guru 317260 points

    The datasheet says in section 8.3.4:

    The INH function is on in all modes except for sleep mode.

    There is no CAN transceiver that pulls INH low by default. How would it differentiate between vehicle assembly and actual usage? If the MCU can detect vehicle assembly, then it is the MCU's job to put the transceiver to sleep. If you want to disable the regulator without involving the MCU, then you have to add a hardware switch (software cannot be involved because the MCU does not power up).

  • 0
    TI__Mastermind 26806 points

    Shyamasundar,

    Clemens's analysis is correct; the TLIN1043A-Q1 brings INH high upon power-on, which is considered a POR condition. It is expected in a system that VCC/VIO will not be present yet, as the INH pin would be expected to be the trigger to activate the power supplies. For this reason, the UVIO/UVCC behaviors are not going to override a wake-up including a POR.

    While some of the CAN transceivers and SBCs have the capability to selectably mask INH, this is done in volatile register sets. PORs will universally generate INH = HIGH.

    However, note that the TCAN1043A-Q1 has a built in sleep wake-up timer that brings the device back into Sleep mode (and brings INH low) when the transceiver is not transitioned into Normal mode. If the MCUs are not activating properly, then this should turn the system back off (normally around 4 minutes, see the data sheets for the particular components). If they are activating "properly" then the MCU needs to bring the system to sleep.

    Best,

    Danny