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Original question:

UCC3808A-1: High magnetizing current in Push Pull topology and effects in current measurement

UCC28083: SLUA584A - How to Specify the Current Sense Resistor in a Converter Using the UCC28083 - Missing Current Sense Gain

David Cano30
Prodigy 210 points
Part Number: UCC28083

Hello everyone,

I am designing a current sense resistor so that I can use it in the Current mode controller UCC28083 (http://www.ti.com/lit/ds/symlink/ucc38085.pdf). The inconsistency that I have found is that in the aplication note where it is explained how to achieve that (application note SLUA584A http://www.tij.co.jp/jp/lit/an/slua584a/slua584a.pdf) is that the current sense gain, which has a value of 2.2 -see 4 page of the datasheet-, was never included.

Should I Include properly that current sense gain value in equations 11, 12 and 13 of the application note (page 5)?

Thank you for your help.

Best regards,

David.

  • 0
    TI__Mastermind 31580 points
    Hi David,

    There is no gain block associated with the CS signal, the gain described in the datasheet is the effective gain between the COMP signal and the CS signal.

    In the controller there is a 0.3V dc offset to give the CS signal a DC bias. This allows the comp signal to command zero duty cycle without have to go all the way to 0V, which is difficult to achieve due to on-state drops and Vbe's in semiconductor devices.

    The COMP pin voltage is also then divided down by an resistor network of 80k/60k which reduces the COMP pin voltage to a similar range and the current sense signal or viewed from the current sense input it scales up the CS input voltage with respect to the COMP pin voltage.

    I hope this helps.

    Regards

    Peter
  • 0 in reply to Peter Meaney
    Prodigy 210 points
    Peter,

    Thank you very much for your help. Really.

    Regards,

    David