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Question about TPS54335 compensation resistor value

Go
Genius 4220 points

Hi,

My customer calculated the compensation resistor value of TPS54335 according to the formula (10)

in TPS54335 D/S. and also did the Webench simulation.

As compared to these two results,  the compensation resistor value is considerably different.

(Please see the attached files)

Where does the difference come from?

Thanks

Go 

TPS54335_500kHz2.0A_10to20Vinput.pdf
  • 0 in reply to Go
    TI__Guru**** 191445 points

    The datasheet equation you used is just a simple approximation assuming ideal current mode control with no slope compensation.  It may also pick a different crossover frequency than Webench.  Webench will use an iterative process to solve for a crossover frequency that will yield the desired phase margin (>60 deg is the default).  Then use k factor to set the poles and zeros, so I would expect a very different result.  Rcomp sets the crossover frequency for a particular LC filter combination and output voltage.  Personally, I prefer and recommend pspice modeling to derive the compensation values.  See the example starting on page 19 of the datasheet.