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TPS92691: tps92691 unstable dimming

Unknown Matsevich
Prodigy 60 points
Part Number: TPS92691

Hello. I make led driver based on tps92691 sepic evolution board, all components as on this eval board but PWM dimming on 1Khz not stable work  in some points from 10 to 15V Vin. Led current is set 0.8A number of leds 8 on 1-10% dimming work is unstable. I try change PWM frequensi but it work unstable in other points Vin. What a can do? Or i need other Led controler chip? My application need stable work 8 leds on current 0.8 A Vin 10-30V 1-100% dimming and output current report.

  • 0
    TI__Intellectual 2590 points

    This is a very complex request and can't be answered with this information only.  A SEPIC converter is a 4th order control system and you are PWM dimming at a relatively high frequency of 1kHz.  I also know what you mean by unstable.  Please attach waveforms of the unstable operation.  Please include zoomed in and zoomed out versions to see both the PWM frequency and the switching frequency.  Include the switch node of the SEPIC converter and the output current at a minimum (other voltages of interest in the system will be the PWM dimming input and the IMON pin voltage if you have a 4 channel oscilloscope).  Finally, please indicate whether you have a coupled inductor or 2 separate inductors and what are the value(s).  Also, what is the switching frequency?

    -JP

  • 0 in reply to James Patterson
    TI__Mastermind 18890 points

    Hello,

    We have not heard back from you so we believe you have solved the issue.  The thread will close now but reopen if you reply.

    Thanks Tuan