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DRV8231A: IPRPOPI resistance

Shuhei Goto
Expert 4880 points
Part Number: DRV8231A

Tool/software:

Hi team,

It seems that the current mirror error get large if R_IPROPI is small(100ohm to 500ohm ).
Is there any recommendation value of R_IPROPI?

Best regards,
Goto

  • +1
    TI__Expert 4770 points

    Hi Goto, 

    Thank you for your question. 

    Shuhei Goto said:
    It seems that the current mirror error get large if R_IPROPI is small(100ohm to 500ohm ).
    Is there any recommendation value of R_IPROPI?

    Yes, the IPROPI pin outputs an analog current proportional to the current flowing through the low-side power MOSFETs in the H-bridge scaled by AIPROP which is 1500uA/A. 

    As the IPROPI (μA) = (ILS1 + ILS2) (A) x AIPROPI (μA/A) the IPROPI is in the range of mA.   

    The corresponding IPROPI voltage to the output current can be calculated by:

    VIPROPI (V) = IPROPI (A) x RIPROPI (Ω)

    Also, the current chopping threshold (ITRIP) is set through a combination of the VREF voltage (VVREF) and IPROPI output resistor (RIPROPI). This is done by comparing the voltage drop across the external RIPROPI resistor to VVREF with an internal comparator.

    ITRIP (A) x AIPROPI (μA/A) = VVREF (V) / RIPROPI (Ω)

    For example, if VVREF = 3.3 V, RIPROPI = 1375 Ω, and AIPROPI = 1500 μA/A, then ITRIP will be approximately 1.6 A. 

    So you can define the RIPROPI based on your settings as stated above. 

    Please let me know if you have any more question. 

    Best regard, 

    Mojtaba

  • 0 in reply to Mojtaba Afshar
    TI__Expert 4880 points

    Hi Mojtaba,

    Thank you.

    Now I understand the V_IPROPI should be the appropriate value for the monitoring ADC.

    BTW, does a small R_IPROPI affect the accuracy or noise of A_IPROPI?
    What is the recommended range of R as a driver IC?

    Best regards,
    Goto 

  • 0 in reply to Shuhei Goto
    TI__Expert 4770 points

    Hi Goto,

    Thank you for your question. 

    Shuhei Goto said:
    BTW, does a small R_IPROPI affect the accuracy or noise of A_IPROPI?

    The AIPROPI gain accuracy depends on several factor. TI provided the AIPROPI gain error vs. Iout_LS current as shown below. So the error is higher for low output currents. The IPROPI set the ITRIP value based on  

    ITRIP (A) x AIPROPI (μA/A) = VVREF (V) / RIPROPI (Ω)

    So, using small RIPROPI provides higher ITRIP values and higher IOUT and higher AIPROPI gain error. So the RIPROPI should be selected based on appropriate ITRIP for your application. 

     

    What is the recommended range of R as a driver IC?

    There is no typical value for R value and It depends on Vref, Itrip values in your application.

    For example, if VVREF = 3.3 V, RIPROPI = 1375 Ω, and AIPROPI = 1500 μA/A, then ITRIP will be approximately 1.6 A. 

    Please refer to datasheet DRV8231A 3.7-A Brushed DC Motor Driver with Integrated Current Sense and Regulation datasheet

    P: 13 Section 8.4.2 Current Sense and Regulation (IPROPI) to set the appropriate R value for your application. 

    Please let me know if you have any more questions. 

    Best regards,

    Mojtaba