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TPS92602-Q1: Loop Compensation Calculations

Richard Leath
Prodigy 240 points
Part Number: TPS92602-Q1

I'm trying to calculate the compensation components according to the equation in section "9.2.1.2.11 Loop Compensation" of the datasheet, but I get strange values.

I have 15 LEDs in the string. Current is 700mA.  Voltage is 55V.  My supply is 19V.  Duty cycle = 67%.  Dynamic LED impedance is 15ohms.  L = 22uH. Cout = 10uF.

Using equations 39 - 44 on p25 of the datasheet, I get Rcomp = 671 micro-ohms, and Ccomp= 385uF!!

My fp is 1230Hz, and fzrhp is 61.9kHz.  My Rsense is 0.2 ohms.  My Risns is 0.022 ohms.

Can you tell me what I am doing wrong?  I was expecting to get Rcomp ~= 500ohms.

By the way, the circuit works fine using the values in the datasheet:  Rcomp = 510, Ccomp = 0.22uF.

I just want to understand why I get such strange values.

Thanks,

Richard

  • 0
    TI__Expert 5475 points
    Hi Richard,


    The equations in the datasheet is for reference only. Sometimes it won't get reasonable results. But the values in the datasheet and EVM have been verified to be fine on most of customers' designs. You can use these values first and make adjustments according to the test results.

    Best Regards,
    Shirley He