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TPS61196EVM-600: Modifications for 20mA drive

Wayne Eckertson
Prodigy 170 points
Part Number: TPS61196EVM-600
Other Parts Discussed in Thread: TPS61196, , LP8556

I have attempted to modify a TPS61196EVM-600 to support two strings of 20mA LEDs but the TPS61196 does not appear to be starting up.  I do not see any switching of the switching node and the Fault line is being driven low.

My LED strings are:

  • Green, Qty 12, 3.2Vf, total Vf of 39.6V
  • Blue, Qty 12, 3.3V, total Vf of 48V

I have modified my TPS61196EVM-600 with:

  • Changed R26 to 240K to set current to 20mA
  • Changed R23 to 160K to set head room to 200mV
  • Changed R24 to 750K to set V(led_short) to 4V

Is there some other modification needed to allow the eval board to run with this LED setup?  Thanks in advance for the help. 

  • 0
    TI__Mastermind 22745 points

    Hi Wayne,

        We don't suggest to use TPS61196 to drive 20mA application since this device is designed for high current and high voltage application. There is a simple work around: set the full scall current to 50mA and set the PWM duty cycle less than 40%, that may be a solution.

    Regards

    Sean

  • 0 in reply to Sean Zhou
    Prodigy 170 points

    I need to check to see if the LEDs can handle 50mA spikes.

    As a secondary option, can you recommend a current controller that can provide four channels of 20mA?

    Other requirements...

    • Vin 12V
    • 4 channels, individually controllable.
    • PWM not required if 20mA is achivable
    • Total Vf is 40V (48V max)
    • Eval board available for quick testing

  • 0 in reply to Wayne Eckertson
    TI__Mastermind 22745 points

    Hi Wayne,

         LP8556 maybe a good solution. What's your meaning about "individually controllable"? You want to change each channel current or turn on/off each channel. I'm afraid LP8556 can't change each channel current but you can turn on/off each channel individually.

    Regards

    Sean