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DRV8711EVM: abnormal behavior after power down

Part Number: DRV8711EVM

Hi team,

Here's an issue from the customer may need your help:

Under normal test conditions, an external control board is used to control, and multiple measurements are ok.

It works properly before power-down, and after several minutes of power-down, here comes the problem: C7, C8 capacitors are shorted, C2, the capacitance of C3 capacitor changes to around 100uf and the 10-pin step_AIN1 of the chip is shorted to GND (not measured before so not sure if it is good previously).

Could you help check this case? Thanks.

Best Regards,

Cherry

  • Hi CHerry,

    Under normal test conditions, an external control board is used to control, and multiple measurements are ok.

    Can you clarify what you mean with this statement? Are they using an external board to control the driver in the EVM?

    Regards,

    Pablo Armet

  • Hi Pablo Armet,

    Thanks for your support and just got the clarifications from the customer:

    An external monolithic device is used to send a pulse signal to control the drive, power-up fails after a period of power-down, and the external monolithic device also be burned.

    The test found that pin 10 step_AIN1 was shorted to ground and reset pin was shorted.

    Thanks and regards,

    Cherry

  • Hi Cherry,

    In order to connect an external signal to the EVM the connection between the driver and the MCU should be removed. If STEP_AIN1 is coming from an external signal, the shunt on the J6 should be removed so it does not collide with the MCU.

    Regards,

    Pablo armet

  •  Hi Pablo armet,

    That's what they did when testing.

    Does a device power down shunt to the upper computer? Is there any effect when the DECMOD register is used to force-fast-decay at any time or always use mixed-decay? Because the motor vibration is significantly less, and the heat generated by running the motor for a long period of time is much better.

    Thanks and regards,

    Cherry

  • Hi Cherry,

    Thanks for confirming.

    Does a device power down shunt to the upper computer?

    I don't really understand your question. can you clarify?

    Is there any effect when the DECMOD register is used to force-fast-decay at any time or always use mixed-decay?

    DECMOD changes the decay mode during the current regulation phase. This app-note explains the difference between these decay modes. But essentially, fast decay lowers the motor current much faster compared to slow or mixed decay when in the motor decay phase of current regulation. 

    I want to take a step back and really understand the issue. So the issue is C7, C8 capacitors are shorted, C2, the capacitance of C3 capacitor changes to around 100uf and the 10-pin step_AIN1 of the chip is shorted to GND? can you provide more details on this. Are the capacitors getting damaged? is the board becoming too hot?

    Regards,

    Pablo Armet

  • Hi Pablo Armet,

    Let's take a look at the situation now:

    C7, C8 are not shorted after the chip is removed from the board. It can be sure that both pins of the chip are shorted to ground, after replacing a new chip, short issue disappear. 

    But C2, C3 capacitance is measured on the board to be more than 100 uf. Is it due to several capacitors in parallel? And does the device have an impact by setting DECMOD in the 0x04 register to Force fast decay at all times or use mixed decay at all times?

    Also, could you help provide the source code provided by the test board master MSP430? 

    What is the maximum current allowed to input on 10-pin? 

    Thanks and regards,

    Cherry

  • Hi cherry,

    the code can be downloaded from tge ti.com tool page of the drv8711evm.