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TPS61199 driving LEDs with shunt protectors

FZ37
Intellectual 450 points
Other Parts Discussed in Thread: TPS61199, TPS61199EVM-598, TPS61196

Using TPS61199 to drive two LED strings. One string with shunt protectors. The other one not.

IFB1-4 to drive one string and IFB5-8 to drive the second one. TPS61199EVM-598 is used with default settings. So each string sees ~240mA current.

Here are the waveform on the IFB pins. Ch2 is the string with shunt protectors. One LED was taken out to see the protector active working. The voltage settling time is quite long (~10us). And the TPS61199 device seems not liking it and turn these channels off after one or two seconds (See second picture)

Tried to put a 33nF cap on the IFB pins to ground. Still did not work although the surge was damped.

Any suggestions are greatly appreciated.

  • 0
    TI__Intellectual 1780 points

    Hello Fz,

    What is the forward voltage of your LED?

    The headroom on the CH2 in the first waveform is 7.1V, which is very high. Interestingly, it corresponds with the breakdown voltage of the NUD4700 (that you mentioned in the TPS61196 post.

    As the headroom here exceeded the threshold VLED_Short = ~6.1V, TPS61199 turned off. So, waveform 2 is expected. The slight switching might be just coupling noise from CH1.

    Best,
    -Harini

  • 0 in reply to Harini Sankabattula
    Intellectual 450 points

    Hi Harini,

    I don't know why. I have 6 strings of LEDs (18 each). One string with the protectors. When ever I have the one with protectors connected, the surge at the beginning will happen. The way the protector works is snap back after it turns on. I did not see that big of surge on TPS61196 on the same string.

    Thanks,

    FZ