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DRV8714-Q1: OSC and OOL

Chong Yu
Intellectual 1435 points
Part Number: DRV8714-Q1

Hi team,

My customer need assistance.

Production datasheet for DRV8714S-Q1, Chapter 8.3.8.12:  www.ti.com/.../drv8714-q1.pdf
the description is <The device provides the necessary hardware to conduct offline short circuit and open load diagnostics of the external power MOSFETs and load.>
Based my understanding, this means external Mosfets -> SC detection, Mosfets -> Open detection, Load -> SC detection, Load -> Open detection, am I right?
If my understanding is correct, I want to know how to detect this four kinds of failures based on VDS_STATUS register bits? 
I think it should be have some combination or other else to help this diagnostic.

Please help. Thanks.

  • 0
    TI__Mastermind 24765 points

    Hi 

    Thank you for your interest in DRV8714-S-Q1. Your understanding is correct except open detection for MOSFET. Open for MOSFET cannot be detected in offline diagnostics, but can be detected in online. After trying to turn on FET, VDS should detect error due to FET is not placed(OPEN). 

    Please refer attached file. It shows example for each shot/open cases. This can be referred for MOSFET short case as well.

    DRV87xx-Q1_Offline_OL_SC.pdf

    regards

    Shinya Morita

  • 0 in reply to Shinya Morita
    TI__Intellectual 1435 points

    Hi Morita,

    Customer replied:
    Thanks for your reply, I think this is very useful to my development projects. Based on your introduction, offline diagnostics should be passive monitoring. As you involved online diagnostics to detect defective FETs, I think which should be active monitoring, what I also interest about it, like how to detect internal cross coupling between FETs, Motor +/- (you can see the picture as below) and so on, do you have this kind of example case for reference, thanks a lot.

  • 0 in reply to Chong Yu
    TI__Mastermind 24765 points

    Hi 

    If shorted like your picture, VDS_overcurrent detection will catch the fault in online. For example, as soon as PU_SHx and PD_SHy are ON, should hit over current level.

    regards

    Shinya Morita

  • 0 in reply to Shinya Morita
    TI__Intellectual 1435 points

    Hi Morita,

    Customer replied:
    In my project, which used two motors (drived by two H-Bridges), Here we have below two diagnostic want to confirm with you.
    1. Refer to picture Motor cross, motors have cross coupling, you can find this is a short circuit between 2 different H Bridges. My question is if VDS_overcurrent detection will catch the fault when PU_SHx and PU_SHy (LEFT) are ON & PD_SHx and PD_Shy (RIGHT) are ON, can we check this over current level to find this kind of fault ?

    2. Refer to picture FETs cross, we also need to check unintended internal cross coupling between FETs in the same H-Bridge and to the passive H-Bridge FETs, can we turn on FETs in sequence then the VDS can detect error, is it right?

    Thanks.

  • 0 in reply to Chong Yu
    TI__Mastermind 24765 points

    Hi

    No1:

    This is not usual case we support. However I think offline diagnostic could work. Online overcurrent protection also could work, but may be detected by only one DRV or both DRV.

    When one of DRV detects OCP earlier than another, second one may not detect OCP.

    I recommend customer verify it on their PCB. 

    How this scenario happens? I am wondering whether they do not have some Poka-Yoke (Preventing error) mechanism like connector, wire connection. 

    No2:

    It is beyond our device protection coverage. 

    Do we know back ground of this? For me, this scenario means external circuit/PCB is really bad.

    Could you share customer's information(via internal e-mail or internal post)? 

    regards

    Shinya Morita