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TPS92515HV: Question about Output current.

Nicky Lim
Genius 3195 points
Part Number: TPS92515HV

Hello,

Make board like as attached Webench circuit and test.

But output current is only 1.18A not 1.25A. 

Test with changing input voltage from 50V to 52V. Output voltage is constant but Current is changed.

This circuit is not constant current circuit?

To get constant current, how can I change the circuit?

Regards,

Nicky

TPS92515HV_LED_2.975V_625mA_16S_2P.pdf

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  • 0
    TI__Mastermind 25500 points

    Hello Nicky,

    It is a constant current regulator but as it is hysteretic (which is why it is so fast reacting to transients and PWM dimming) it regulates the peak inductor current. So your values are correct as calculated, however due to certain tolerances such as the inductor possibly being a little less than 15uH at current the Roff value often needs to be tweaked a little for the application. In your case probably the next lower value. 70mA isn't far off so it shouldn't be difficult.

    Having said that it is possible there are noise issues too. How much does the current change between 50V and 52V? It will change a little bit, but it shouldn't change much. Is this built up on an EVM for your own board? If it is your own I'd be happy to check the layout for issues. Could you take a scope shot of the switching node? That will almost always show you if you have noise issues that could affect regulation.

    Regards,

    Clint

  • 0
    TI__Mastermind 25500 points
    By the way, I would try a different diode as well. D1 is huge and oversized and likely to introduce a lot of parasitics that can cause noise.