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DRV8870: over-current detection

Nicolas Lecordier
Prodigy 10 points

Part Number: DRV8870

Dear TI Team,

We are using the DRV8870 device since many years on one of our product.

It's driving a small DC motor.

The DRV8870 is suppyed in 24V, and its commands are in ON/OFF 0_5v signals on its 2 inputs (IN1 and In2) to move the motor in the 2 rotations.

The sense resistor is fixes to 1 ohm, and Vref is 3V, which indicate a current limitation of the devide to about 300mA.

We can observe it with devices which are running, at the beginning of the rotation of the motor, output out1 or out 2 are switch on and off to "regulate " the current to 300mA for about 200msec.

It was well working since many years, but we have now troubles with it, motor doesn't start it rotation.

We have observed that the DRV8870 looks to enter directly in over-current limitation cycles, with 3msec off sequence before restart and switching off again.

We have a batch of boards with this behaviour. During checking, we have noticed that a way to start the rotation is to shunt the sense resistor. But we can't explain this behaviour.

Do you know some modifications on the design of the DRV8870 which could explain this, and which modification would be required ? 

Thanks in advance

  • 0
    TI__Mastermind 24580 points

    Hello,

    Please allow us some time to review and we will get back to you with within a day or two. 

    Best,

    David

  • 0
    TI__Prodigy 280 points

    Hi,

    This device was not changed recently. When did you first observe this issue? Do you have a more recent batch that does function correct? If you could send me a list of Lot codes on the top symbol of some of the devices? 

    Best,
    Jason Abell

  • 0
    Prodigy 10 points

    Hi David

    In fact, the system was working since many years (with previous driver ?),  and not now.

    I have noticed the marking of a "non-functionning" device : 

    I   8870

    I      TI49M

    I    A6K1

    and to compare, we also have noticed marking of a functionning device : 

    I   8870

    I      TI 23A

    I    P2F764

    Our batch is about 30 boards and we have noticed the uncorrect behaviour on most of them (maybe one or two boards looks correct).

    Regards

    Nicolas

  • 0 in reply to Nicolas Lecordier
    TI__Prodigy 280 points

    Hi Nicolas,

    By shunting (bypassing) the sense resistor you are disabling over current detection

    Could you describe in detail the load you are driving?

    What type and configuration is the 1 ohm Sense Resistor?

    Also in the mean time could you increase Vref to 5v to see if this changes anything?



    Thank you,

    Jason Abell