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DRV8718-Q1: offline open load diagnostic

Chuqiang Wen
Expert 4560 points
Part Number: DRV8718-Q1

Hi Expert,

My customer is using DR8718-Q1 in their project. They use the channel 1 to control the external power release motor. You can find the schematic as below. 

Based on the reference materials, when enable the offline open load diagnostic, the SHx=SHy=1/2PVDD if there is no fault(no short or open load). 

But the feedback from customer is that both the SHx and SHy voltage are 5.6V no matter the PVDD value is in each voltage level of 9V-16V. It seems can not meet the description of spec(SHx=SHy=1/2PVDD). 

Could you please give some comments for this case? 

Thanks!

Ethan Wen

  • 0
    TI__Mastermind 24615 points

    Hi,

    Thank you for your question. Let me review the contents and feedback to you in 24 hours.

    regards

    Shinya Morita

  • 0 in reply to Shinya Morita
    TI__Mastermind 24615 points

    Hi Ethan,

    In Offline diagnostic,  pull up current and pull down current is 3mA typ. If load condition is normal, SHx=SHy= 1/2PVDD. I am wondering R140 or R141 impact to this balance and generating some voltage by R_load x 3mA. Or if customer has some additional load on SHx and SHy, voltage could not be 1/2PVDD.

    I suggest to remove R140 and R141 to find the root cause.

    regards

    Shinya Morita

  • 0 in reply to Shinya Morita
    TI__Expert 4560 points

    Hi Shinya,

    Thanks for suggestion!

    The R140 and R141 are the thermistors. Customer tried to remove these two thermistors and change the motor load to resistor load(2.5ohm/300W). But the SHx/SHy still not equal to 1/2 PVDD. You can find the waveform as below. Their open load diagnostic strategy is periodically 3s active mode, 300ms offline open load detection. We can see the SHx/SHy is increasing when PVDD increase from 9V to 12V. But the SHx/SHy keep the same voltage when PVDD increase from 12V to 15V. 

    Do you have any other suggestions? Or could you please share our waveform for offline open load detection to show the 1/2 PVDD when there is no open load fault? 

    This project is going to production right now. Appreciate if you can give some comment by today. I will have meeting with customer late today. 

    PVDD=9V, SHx/SHy=~4.5V

    PVDD=12V, SHx/SHy=~5.3V

    PVDD=15V, SHx=SHy=~5.3V

    Thanks!

    Ethan Wen

  • 0 in reply to Chuqiang Wen
    TI__Guru 54645 points

    Ethan,

    Morita-san is out of the office today. 

    Are they sure they are enabling BOTH the HS and LS current sources as shown in the figure?  

    Regards,

    Ryan

  • 0 in reply to Ryan Kehr
    TI__Mastermind 24615 points

    Hi Eathan,

    As discussed separately, 1/2PVDD is not correct information. SHx voltage is not defined in this situation. Material will be updated.

    regards

    Shinya Morita