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Original question:

TPS92691: LED driving problem

TPS92691: OVP tuning

Roman Simonyan
Intellectual 440 points
Part Number: TPS92691

Hi. Dear friends, please explain to me:

1. How to choose and tune the OVP (how much above the working voltage it should be).

2. How much the OVP hysteresis should be and how it works?

Thank you for help.

Roman

  • 0
    TI__Mastermind 18890 points

    Hi Roman,

    The over voltage should be a about 3V above the maximum output voltage depending on your application it can be higher.  While the hysteresis should be about 2V below your maximum output voltage.

    The main intend of the OVP is to prevent the output voltage from going too high to damage any parts on the board in case of an open circuit.

    Thanks Tuan

  • 0 in reply to Tuan Tran74
    Intellectual 440 points

    Dear Tuan, thank you for your help. Several additional questions:

    1. Do I understand hysteresis mechanism correctly: when overvoltage occurs, system shuts down and starts again only when the voltage goes below OVP voltage by amount of hysteresis volts?  So, if I have 56V target voltage, and 60V OVP, is it better to go closer to target (say 55V, 5V hysteresis) or OVP (say 58V,  2V hysteresis)? If possible say several words on why.

    2. As the IC was damaged several times previously, I guess there were spikes peaking above the ic's max 65V, will a 62V zener across the LED protect the IC?

    Thanks,

    Roman

  • 0 in reply to Roman Simonyan
    TI__Mastermind 18890 points

    Hi Roman,

    1.  Your understanding is correct.  Where you set the OVP and hysteresis is a system level questions and requirements.

    2.  You need to verify that the LED forward voltage max does not feedback to the TPS92691 any voltage above 65V.  If the max LED forward voltage is above 62V then with a 62V zener all the current can go to the zener in addition, the zener clamp voltage max and min needs to be taken into account.  I would not use a zener.  Need to verify that max LED forward voltage is not above 62V.  The part is IC should not damage if that is the condition.