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DRV8428: what is the leakage current at Vref pin?

Lenio Cacula
Genius 16700 points
Part Number: DRV8428

What is the leakage current at Vref pin? My customer needs to determine the values of the voltage divider and the capacitor for PWM control. Without knowing the leakage current it is difficult to determine those components, despite the fact the datasheet recommends less than 50kOhms. We are also trying to understand if R2 needs to be of a minimum value or not.

Thank you!

  • 0
    TI__Guru 56650 points

    Lenio,

    In the datasheet, "It is recommended that the value of parallel R combination of RREF1 and RREF2 should be less than 50-kΩ."

    If we know the pull-up source Vp and want to set VREF,  we have two equations:

    VREF=Vp* Rbottom/(Rtop+Rbottom)

    Rparallel = Rtop*Rbottom/(Rtop+Rbottom)=50kohm;

    We got VREF=Vp* 50kohm/Rtop

    So, Rtop=Vp*50kohm/VREF

    According to the datasheet recommendation, the calculation doesn't need to know the VREF leakage current.

    Regards,

    Wang Li

     

  • 0 in reply to Wang5577
    TI__Genius 16700 points

    We need to calculate the equivalent resistance and the leak current for properly dimensioning the RC filter for PWM control. We also want to understand the reasons behind the recommendation of 50kOhms and how much error we incur from moving closer or farther of this number. 

  • +1 in reply to Lenio Cacula
    TI__Guru 56650 points

    Lenio,

    The reason behind the recommendation is the Rbottom/(Rtop+Rbottom) cancelation from the above two equations. So, we can have a simple equation for Rtop and Rbottom.

    I would think the VREF error is less than 1% if we follow the recommendation. 

    BTW, I have search the characterization file, we don't have the VREF leakage current parameter.

    If we have to estimate it, the maximum leakage make 1% error, the worst Case:

    Vp=3.3V, VREF=Vp/2; Rtop=Rbottom= 100kohm, the current in Rtop and Rbottom is 3.3V/200kohm= 16.5uA. 1% 16.5uA is about 165nA.

    Regards,

    Wang Li