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DRV8848: Outputs are grounded, even while all input conditions are satisfied

Jakub Czarny
Prodigy 10 points
Part Number: DRV8848

I'm implementing a very minimal setup for the DRV8848 and I can't get it to output anything. Already tried a 50% PWM on AIN1 and low on AIN2, and just a HIGH and LOW on those pins. The fault and sleep pins are both high and all other voltages are within spec (7.2V on VM and 3.3V on VINT and VREF). I can see that all the outputs are grounded even without any load plugged in.

I've included my schematic and layout as well. I tried all troubleshooting steps I can think of, so any kind of help or ideas on what to check would be greatly appreciated.

  • 0
    TI__Mastermind 21660 points

    Hey Jakub,

    Have you tried replacing the DRV8848 chip, in case the device is not soldered correctly or was damaged in the process? Or tried multiple boards?

    Jakub Czarny said:
    I can see that all the outputs are grounded even without any load plugged in.

    This implies to me the device damage, since the outputs would be Hi-Z (high impedance) if the device was in a fault condition.  They should only be GND if IN1 and IN2 are both HIGH 

    Schematic looks pretty good to me.  I see you have AISEN and BISEN tied to GND, so current regulation is not used. Do you have more bulk capacitance somewhere else?  10uF is not much. 

    For your layout if you make a new revision of the board you need to remove the thermal relief connects on the device, with those you won't get nearly as good of thermal performance as without it.  See Best Practices for Board Layout of Motor Drivers.

    Best,

    Jacob

  • 0 in reply to Jacob Thompson
    Prodigy 10 points

    Hi Jacob,

    I've already tried a 2nd chip, so the case of damage seems less likely, but I can try another one.

    I have more capacitance near the motors themselves, so hoping that is enough. I'll keep your suggestions in mind for the 2nd revision, but still struggling to find why it will not operate even without a load present.

    Regards,

    Jakub

  • 0 in reply to Jakub Czarny
    TI__Expert 8660 points

    Hi Jakub,

    The SLEEP pin is already configured with an internal pull-down resistor. Try removing the 10kΩ resistor on the SLEEP pin. 

    Best,

    David

  • 0 in reply to David Medis
    Prodigy 10 points

    The pin needs to be high to be enabled, the internal pull-down would put it to sleep.

  • 0 in reply to Jakub Czarny
    TI__Expert 8660 points

    Hi Jakub,

    I would suggest verifying all the pin voltages on the board. Make sure all voltage values fall within the recommended operating conditions. 

    Where were the DRV8848 motor drivers purchased? Where purchased made through TI.com or an affiliated distributor? 

    Authorized Distributors

    Best,

    David

  • 0 in reply to David Medis
    Prodigy 10 points

    All voltages have been double-checked with 2 different instruments and fall within operating conditions. The parts were purchased through RS Components in UK. At this point I have gone through 3 chips now and either the whole batch is damaged or the chips must not be surviving the hot air reflow.

    Best,

    Jakub

  • 0 in reply to Jakub Czarny
    TI__Mastermind 21660 points

    Hey Jakub, can you post a picture of the top of one of the devices so that I can read the markings on it? I want to run it through our system to confirm they aren't counterfeit. 

    I'm sure you did, but did you confirm the device is in the correct orientation on the board? No observed solder bridges on the leads after soldering?