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TPS62933: Current sense resistor position

Steven Wang
Prodigy 230 points
Part Number: TPS62933


Hi,

1) Should I put current sensing resistor before or after the feedback node?

2) If I change the RT ressitor, the operating frequency will be changed. Should I change any component's value? 

3) Is there any other issues for my design?

Thanks 

  • 0
    TI__Genius 16632 points

    Hi Steven,

    1. I think should place the Rsense after Cout, to get a filtered/stable output current. Otherwise you are measuring inductor current which is sawtooth and varying.

    2. Please follow datasheet LC table for different fsw.

    3. Please add 2*10uF+1*0.1uF input caps. I didn't see Cin.

  • 0 in reply to Miranda Gu
    Prodigy 230 points

    Hi Miranda, thanks for the support. 

    The current sense resistor R16 is used for measuring the output current to the load. I would like to have a stable Vout for full current load range. In another thread, you suggested me to place the current sense resistor R16 before the feedback loop to avoid the minor voltage drop at the output side (10mOhm*3A = 30mV voltage drop). Could you confirm this R_sense position question with you RD team, please? This is a key parameter for a precise DCDC load measurement. 

    Thanks a lot 

  • +1 in reply to Steven Wang
    TI__Genius 16632 points

    Hi Steven,

    Thanks for your quick feedback.

    I mean should place Rsense after Cout, not before Cout (as you did), that's NOT related to Rfb.

    I think it's OK put it either before Rfb or after Rfb. If you have a strict requirement on Vout accuracy and don't want 30mV voltage drop at loading side, you can place Rsense before Rfb. If 30mV voltage drop can be accepted by your loading, you can place Rsense after Rfb.