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TPS61196: how to understand diode open and short protectioon

david sun77114
Expert 2140 points
Part Number: TPS61196

Dear Support, 

I am using TPS61196 to drive 3 12LED chains( roughly 75V), the diode open and short protection is a very important feature in this application. but the data sheet didn't provide detail. it's easy to understand an open diode will make the current of whole chain to 0. if one diode in the chain short and all rest of the diodes are still working, can TPS61196 detect and report this fault condition?

Thank you very much. 

David

  • 0
    TI__Mastermind 29010 points

    Hi David,

    The Schottky diode short will cause the output capacitor reverse current flow back through switching MOSFET to GND. Thus will cause cycle by cycle current limit protection. 

    And the output voltage will drop rapidly so that all strings will force into open protection as well. The TPS61196 will be latched off.

    BR

    Patrick

  • 0 in reply to Patrick Yao
    Expert 2140 points

    Hi Patrick

    I don't think you answered my question.  what do you mean Schottky diode short? I use TPS61196 to drive a 12 LED in serial. is it possible to know if one of the 12 LED is short but all the rest of 11 LEDs are still function?

    Thank you,

    David

  • +1 in reply to david sun77114
    TI__Mastermind 29010 points

    Hi David,

    So you are actually asking about the LED open and short fault, right? Sorry I misunderstand it as the diode in boost topology which is also listed as fault in datasheet.

    To answer your question about LED short. You can refer to datasheet page 16 "7.4.1.3 LED Short-Cross Protection Using the FBP Pin". You can set a threshold voltage, once the IFB pin voltage exceeds this threshold, the related LED string will be cut off.

    For example, you set the threshold voltage as 5V and IFBV as 0.4V, and your LED Vf=3V. If during operation, one of 12 LEDs short, the IFB pin voltage will be 3+0.4=3.4V, but still lower than threshold, so TPS61196 will continue to sink the current to this string. But if over 2 LEDs short, the IFB pin voltage will then over 5V threshold, so TPS61196 will stop sinking current for this LED string.

    BR

    Patrick

  • 0 in reply to Patrick Yao
    Expert 2140 points

    thank you very much, I need sometime to understand it, but it is just what I need.

    David