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DRV8302: unexpected 3-5s delay when Driving a BDC motor

Yue TANG
Genius 9045 points

Part Number: DRV8302

Hi experts,

My customer is using a DRV8302 to drive two BDC motor. 

they first tried  as below with highside current sensing, it works fine. VDD is about 24V 

but to save cost, they changed to low side current sense and use below way to drive the same BDC. motor can run , but every time, there is an unexpected 3-5s delay before it runs. 

they don't understand what went wrong. 

Please kindly suggest if something wrong here.  

  • 0
    TI__Mastermind 18900 points

    Hello Yue,

    I'm not sure how of the process to spin your motor but we need to isolate where the delay in the process is occurring. Can you probe EN_GATE, a INx signal and corresponding Gx signal and see if the INx PWM is coming in, being received, and then there's a 3-5s delay from the Gx signal appearing? If so, we'll need to start debugging there.

    if not, the DRV8302 is not at fault. What I mean by this is the algorithm, control, or method to controlling the motor is delaying the PWM signals on INx by 3-5s. I would assume this would be a software bug.

    Best,

    -Cole

  • 0 in reply to Cole Macias
    TI__Genius 9045 points

    Cole,

    Sorry for delay due to holiday. Honestly, this is the first time I see use a BLDC device to drive a BDC motor, but my customer do have used this in their

    products, they need to drive 300W-500W BDC. appreciate if you can recommend  suitable TI BDC device 

    please let me simply explain how it works,as above first picture show, turn on high side MOS, turn off low side MOS, then BDC spin.  turn off high side

    MOS, turn on low side MOS, then current decay ,motor stop spinning. 

    however ,they have to use below aprroach due to cost and  some structure related problems, if can't solve they will change to other solution. 

     I also think using like this may have problem, but the motor do can spin, just had some seconds delay.  I know it's a tough question, just help to confirm

    if this BLDC devie  can  be used to drive a BDC ? thanks. 

  • 0 in reply to Yue TANG
    TI__Mastermind 18900 points

    Hello Yue,

    Comments

    Yes, the DRV8302 can be used to drive a brushless brushed DC motor, their configuration is correct for that. They have the right idea for commutation to make the motor spin, as you've explained for the top picture.

    Theory about DRV8302:

    For some introductory knowledge, the DRV8302 is a bit of a translator. Digital signals come into the INHx and INLx, the voltages are then scaled to GVDD+PVDD and GVDD to GHx and GLx, respectively. Input and output are square waves and, in general, Gxx will follow INxx signals, assuming all rails are powered up and EN_GATE is asserted.

    Follow up steps:

    According to the datasheet, there is no reason for the device to delay any once INxx signals come in. The exception to that rule is if there is a fault, which is displayed on the nFAULT and nOCTW pin (which can be decoded by table 5 Fault and Warning Reporting and Handling). 

    Assuming there is a fault, look at the criteria in the table and see what could be problem.

    Assuming there isn't a fault, they need to provide waveforms of INxx and Gxx to see if INxx is present and Gxx is not.

    Best,

    -Cole

    Edit: brushless to brushed