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DRV8711 false PRE-DRIVER FAULT when current compensated chokes are used

Michal Novak
Prodigy 140 points
Other Parts Discussed in Thread: DRV8711

Hi,

The PRE-DRIVER FAULT (xPDF) occurs after drivers are enabled (when the DRV8711 is cold). PCB and MOSFETs are OK.  Setting of the DRIVE register has no influence (50 mA, 100 mA, 150 mA, or 200 mA). Serial resistors 10R connected between output DRV and gate of the MOS have no influence (a schematic file is enclosed). 

What can be the reason? How is the excessive current exactly detected on the gate drive outputs?

The problem can be that current compensated chokes 500uH are used in every phase of the stepper motor (to avoid EMI). 

(The Fault  disappears typically when the temperature of DRV8711 rise up to 50°C.)

Our set: DRV8711DCP + Mosfet PSMN045-80YS (80V,45mR,24A, total gate charge Qg=12,5nC), supply voltage Vm=48V, max current of the phase 3A.

(Additional question which has no relation to upper problem: Can small RC filter on sensing inputs xISENP and xISENN be useful? The current has some noise.) 

Thank you!

Michal

   

  • 0
    TI__Mastermind 26065 points

    Hi Novak

    I have an experience that the issue may also related to the Qg of the FETs. With all same conditions, FETs with 40nC will show no nFAULT while FETs with 10nC assert the nFAULT more easily.

    Could you tell us what's your decay modes setting? we will try with similar conditions. Also you can try auto-mixed decay, and it will give less all types of nFAULT trip.

    We will look at this more inside and get back to you later.

    Thanks.

    Wilson Zuo

    Motor Application Team

  • 0 in reply to Wilson Zuo
    Prodigy 140 points

    Hi Wilson,

    thank you for your quick answer!

    We use the decay mode (010: Force fast decay at all times). Our stepper motor has 14mH and we obtain the best results using this mode (noise, vibration).

    Thank you!

    Michal