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DRV8701: MOSFET selection for DRV8701

Supriya Khapare
Intellectual 350 points

Part Number: DRV8701
Other Parts Discussed in Thread: CSD18542KCS, , CSD18532Q5B

Hello,

We have design Motor driving board using DRV8701. We are facing below issue.

Motor Specifications. PMDC, 24VDC, 500W

When we are using CSD18542KCS MOSFET and our Motor voltage is 24VDC at Motor ON command CSD18542KCS MOSFET burnt. After lots of failures we replace this MOSFET by IRFZ44N then we are not facing MOSFET burning issue. 

Please let me know resolution for this 

  • 0
    TI__Mastermind 24740 points

    Hi Supriya,

    Factors to consider in the selection of external FETs is gate charge (Qg), charge pump current capacity (IVCP), and switching frequency (fPWM).

    The gate charge will also be dependent on the decay mode (SLOW or FAST). Once you calculate gate charge then you can determine the suitable IDRIVE current for FET selection.

    More information on MOSFET selection can be found in section 8.2.1.2.1 of the datasheet. 

    Best,

    David

  • 0 in reply to David Medis
    Intellectual 350 points

    Hello,

    Right now Vm is 24VDC and as per datasheet if Vm > 12V, IVCP = 12mA.

    We are not using any switching frequency at EN and failure observed at Motor inrush current time so I am considering Fpwm is 38 KHz (Internal current chopping As mention in datasheet) 

    Considering above value then QG < 315 nC.

    For IRFZ44NSTR QG value is  67 nC which less than 315 nC 

    Similarly CSD18542KCS QG value is 44 nC which less than 315 nC.

    We are facing failure for CSD18542KCS while as on DRV8701EVM CSD18532Q5B MOSFET is used.

    Please let me know why CSD18542KCS is burning during Motor inrush current

  • 0 in reply to Supriya Khapare
    TI__Mastermind 24740 points

    Hi Supriya,

    The IDRIVE is another important consideration which affects the output slew rate and depends on the FET input capacitance and gate charge.

    The peak source currents are configurable by adjusting the RIDRIVE resistance on the IDRIVE pin.  

    What is the current IDRIVE setting?

    Also, what are RSENSE, and VREF for current regulation?

    Best,

    David

  • 0 in reply to David Medis
    Intellectual 350 points

    Hello Devid,

    Right now Rsense is 20mOhm, and Vref is 0.85VDC. We have set Imax 20 Amp.

    For IRFZ44N Idrive setting 227 mA. 

    For CSD18542KCS we tried for all Idrive combination 

  • 0 in reply to David Medis
    Intellectual 350 points

    Hello Devid,

    Right now Rsense is 20mOhm, and Vref is 0.85VDC. We have set Imax 20 Amp.

    For IRFZ44N Idrive setting 227 mA. 

    For CSD18542KCS we tried for all Idrive combination 

  • 0 in reply to Supriya Khapare
    TI__Mastermind 24740 points

    Hi Supriya,

    The IDRIVE setting is set by the RIDRIVE settings that I shared above.

    I am a bit confused on how you are getting a 227 mA IDRIVE setting. 

    What is the RIDRIVE value and configuration?

    Best,

    David

  • 0 in reply to David Medis
    Intellectual 350 points

    Hello David,

    Sorry.. we are using 68K pull up which allow 150/300 mA.

    But we are not facing issue with IRFZ44N .

    We are facing issue with CSD18542KCS  where we tried all possible combinations

     

  • 0 in reply to Supriya Khapare
    TI__Mastermind 24740 points

    Hi Supriya,

    Could you please provide the answers to the following questions so we are better able to understand this issue?

    1) Are the FETs being configured for high-side or low-side? 

    2) Are you receiving any faults while operating?

    3) After the CSD18542KCS is burnt, is the DRV8701 still functional?

    4) What are the case temperatures of both FETs? What is the temperature the CSD18542KCS is burning at?

    5) How many tests have been run with each of these devices, and how many have failed out of what was built?

    6) How are the FETs being heatsinked to the board?

    7) If possible, could a photo of the layout and board be sent?

    Best,

    David