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DRV8711: DRV8711's prototype burned out two chips

Annie Liu
Genius 10295 points
Part Number: DRV8711

Hi Team,

Customer made prototype board. The board can run at low current (1A), the external motor is 4A. When the customer sets the current to 4A, less than 1 second after starting operation, 24V 2.5A power supply directly overcurrent protection. He cut off the power of the prototype and measured 2R at both ends. He removed the chip and replaced it, it will be normal. Small current can continue to run. The current is increased again, and burned again.

The chip has overheating and overcurrent protection. Customer would like to know what causes it to burn directly?

Thanks,

Annie

  • 0
    TI__Mastermind 37683 points

    Hello Annie,

    What are the register settings the customer used when the IC was burned?

    If possible, can the customer provide their board layout/schematic?

  • 0 in reply to Pablo Armet
    TI__Genius 10295 points

    Hi Pablo,

    The register settings are as follows:

    DrvRegister[Ch][REG_CTRL] = 0x0D10; //ISGAIN = 10
    DrvRegister[Ch][REG_TORQUE] = 0x01C3;
    DrvRegister[Ch][REG_OFF] = 0x000b;
    DrvRegister[Ch][REG_BLANK] = 0x0031;
    DrvRegister[Ch][REG_DEVAY] = 0x030b;
    DrvRegister[Ch][REG_STALL] = 0x0A02;
    DrvRegister[Ch][REG_DRIVE] = 0x0A58;

    Another project is also connected to a 4.2A 57 motor according to this configuration. That has been used normally about 100.
    At present, it is also modified and redone as before, and two samples are welded.

    • One is currently normal, but sometimes a PDF (pre-driver) error is reported. Customer is checking origin.
    • Another one burned out a piece of DRV8711. It runs normally at low current. But it burns out immediately after increasing the current. Customer does not solve the problem after changing two tablets. A few capacitors in the peripheral circuit.

    Thanks.

    Annie

  • 0 in reply to Annie Liu
    TI__Mastermind 37683 points

    Hello Annie,

    Thank you for providing the information,

    A cause of concern with the register settings is that the TOFF is set to 5µs and DECMODE is set to forced slow decay at all times. It is possible that the current does not have enough time to properly decay and the current keeps ramping up past 4A. Depending on the Risense resistor value, the ISENSEx pin abs max voltage could be violated and causing the IC to get damaged.

    Can the customer increase the TOFF to at least 15µs and set DECMODE to 101 (auto mixed decay). Then starting with 1A current and slowly increasing the current by 0.5A all the way to 4A and take a screenshot of the current?

  • 0 in reply to Pablo Armet
    TI__Genius 10295 points

    Hi Pablo,

    DrvRegister[Ch][REG_DEVAY] = 0x030b; 

    DECMODE should be a mixed decay mode, not a forced slow decay mode.

    "Depending on the Risense resistor value, the ISENSEx pin abs max voltage could be violated and causing the IC to get damaged."

    The customer didn't understand it very well. At present he uses a power resistor with a resistance of 0.05 ohms;

    What you said is to adjust TOFF to 15uS and the automatic mixed decay rate. He will try it. Can he increase TOFF to a higher running speed?

    Thanks.

    Annie

  • 0 in reply to Annie Liu
    TI__Mastermind 37683 points

    Hi Annie,

    "DECMODE should be a mixed decay mode, not a forced slow decay mode"

    You are correct, it is mixed decay mode. 

    "Can he increase TOFF to a higher running speed?"

    Yes, there should not be an issue with doing that. 

    What is the RDS(on) of the FET's that the customer is using? I would like to know so I can calculate the maximum current that can go through the FETs before OCP fault is triggered.

  • 0 in reply to Pablo Armet
    TI__Genius 10295 points

    Hi Pablo,


    ID (at VGS=10V) 28A
    RDS(ON) (at VGS=10V) < 35mΩ
    RDS(ON) (at VGS = 7V) < 42mΩ

  • 0 in reply to Annie Liu
    TI__Mastermind 37683 points

    Hi Annie,

    Thank you for the information.

    I reviewed the schematic and layout. Everything looks good. 

    Using the RDSon and Rsense, I calculated the ISENSEx pin voltage to be well below the absolute maximum value. So this should not be burning out the chip.

    Has the customer tried increasing Toff to 15us? What were their results?