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TPS548A20: OCP Rtrip

Trenton Reed
Expert 3010 points
Part Number: TPS548A20

Hi Team,

I have an application for 12V to 1V @ 10A max, 400kHz Fsw, and 800nH inductor (preferred). The datasheet says the Rtrip should be between 20kOhm and 65kOhm but I've noticed a few issues with the Rtrip value. 

  1. Webench defaults to a 68.1kOhm value for 12A OCP threshold. This is outside the datasheet recommended range. 
  2. Inserting 68.1kOhm into equation 4, 820nH (default in Webench), 5.7mOhm RDSonLS_Max, and 68.1kOhm (Vtrip of 681mV) will yield a I_OCP of 16.33A. This doesn't correlate to Webench value of 12A.
  3. I thought there might be an issue with that particular OCP threshold setting so I changed it to 10A and Rtrip was generated for 54.9kOhm which should be 13.43A and not 10A as requested. 

Can you shed some light into the Webench calculation for Rtrip?

What is the correct value to use for 12A threshold?

Thank you,

Trenton Reed

  • 0
    TI__Mastermind 23955 points

    I estimated the 48kOhm for 12A using the equation.     The electrical characterisic table on page 9 for Current limit threshold, valley  11.5 min, 15 typ, 17.5 max for Rtrip=49kOhm.

    I will inform the webench team that the calculation for Rtrip is incorrect and recommends values out range of the datasheet recommendations.