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OPT8241-CDK-EVM: Negative 5V

The Bernd
Prodigy 60 points

Part Number: OPT8241-CDK-EVM

Hi everyone,

I don't understand the negative 5V bias. Is it used like a contrast voltage in an LCD? Why is it also used on the connector to the illumination board?

Thx in advance,

Bernd

  • 0
    TI__Expert 3800 points
    Hi Bernd,

    Negative 5V is a bias voltage which improves the pixel's performance. It is not necessary for the device operation, but we would suggest that you use this supply. This causes a different kind of phenomenon as compared to LCDs.
    It is used as a connector to the illumination board in case any customer designs a custom illumination board and might need a negative voltage on the board. It is not currently used on the illumination board.

    Regards,
    Subhash
  • 0 in reply to Subhash Chandra Sadhu
    Prodigy 60 points

    Thank you for your quick reply!

    Is it recommended to be able to set the voltage between 0 and -5V? I'd otherwise like to use the LM27761 chargepump and bias the feedback resistors using a spare LDO. This way I could save the digital pot (TPL0102-100PWR) and its corresponding levelshifter. I'd be able to set the voltage from -5.062 V up to -2.87 V. The LM27761 can deliver up to 250mA.

    Do you think these parameters are sufficient? What voltage is used in the CDK? I wasn't able to find the potentiometer register beeing set (I had a look here).

    Regards,

    Bernd

  • 0 in reply to The Bernd
    TI__Expert 3800 points
    Bernd,

    You should be able to use a fixed -5V supply and do away with the digital potentiometer altogether. There is no need to have fine control over the voltage.
    You could turn off the -5V supply when it is not needed using a combination of switches controlled by ILLUM_EN. However, if you are trying to primarily reduce component count (and prioritise that to efficiency), you could jut connect -5V to OPT8241 directly.

    LM27761 is a good fit.

    Hope this helps.

    Regards,
    Subhash