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TPS40211 LED reference design ripple current

Emil Eriksson70652
Prodigy 130 points
Other Parts Discussed in Thread: TPS40211, TPS40211EVM-352

Hi,

I'm using the TPS40211 for an LED driver design. Taking into account all the parameters (400 kHz f(s), 10 µH et.c.) in the reference design, I've realized that the peak-to-peak (different datasheets seem to use different ways of measuring, some use I(max) - I(avg)) ripple current in the inductor is approximately 100% of the average current. This seems a bit high to me because in most data sheets for switchers, I've seen about 30% used as a recommendation.

Why is this so high here? If I understand correctly, in a boost topology, the ripple current does not have very much influence on the output ripple since the output is pulsed anyway. The inductor ripple does have a bearing on the input voltage ripple, exactly the opposite situation from the buck converter.

But still, why is the ripple current so high in this case?

  • 0
    TI__Genius 17240 points

    Hi Emil,

    Regarding the TPS40211EVM-352 for LED driver, the inductor is sized to make sure that the converter always runs in CCM to simplify the compensation design. The worst case is when the input current is at the minimum level under high line, low ouput condition. As long as the peak-to-peak inductor current is less than twice of average inducot current (input current), the converter will run in CCM. Then of course, higher inductance, smaller ripple, less RMS current in the switch, diode and output capacitors, but usually bigger size and DCR.

    Regards,

    Na