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LP8860 current programming with hybrid dimming

Orlando Grigoriadi
Prodigy 130 points

Dear all,

Could you please explain the equation found on page 22 of the datasheet of LP8860, which involves the value of the register IDISP_CL1_CURRENT?

The IDISP_CL1_CURRENT is a 12 bit register but it equals to mA (in the two examples 25mA and 2.49mA).

Could you please explain how this conversion in done?

I am using this component and i am facing a problem with how to control the LED current with the GAN_CNTL, DRV_LED_CURRENT_SCALE, DISP_CL1_BRT and IDISP_CL1_CURRENT  registers.

Could you please give the equation of the current which flows through LEDs as a function of the above registers on hybrid dimming mode?

Thank you very much.

Orlando Grigoriadis

  • 0
    TI__Genius 11020 points

    Hello,

    Please see datasheet page 28. for details how to convert register value to LED current.

    Best Regards,

    Tomi Koskela

  • 0 in reply to Tomi Koskela
    Prodigy 130 points
    Dear Tomi,
    Thank you for your reply.

    Since i am using the register values for the max current configuration (DRV_EN_EXT_LED_CUR_CTRL = 0) and i am using the LED driver in display mode (NOT in cluster, LED_STRING_CONF[2:0] = 001) the LED current should be given by the equation (3) found on p.28.

    My problem is that the value given by this equation is verified - measured with an amperometer in series with the LEDs - when i am using the driver in PWM mode (EN_PWM_I = 0 ) but NOT when i am using the driver in Hybrid mode (EN_PWM_I = 1).

    For example, i cannot understand why when using the driver in Hybrid mode ( EN_PWM_I = 1 ) just by changing the GAIN_CTRL registers and keeping the brightness( DISP_CL1_BRT(11:0) ), current ( DISP_CL1_CURRENT(11:0) ), max current ( DRV_LED_CURRENT_SCALE(2:0) ) the same, i change the LED current.

    By keeping brightness, current and max current registers constant when doubling (2x) the GAIN_CTRL register (from 25% (011b) to 50% (000b) ) i half the LED current. Could you please explain why?

    If you want i can share measured values.

    Thank you
    Orlando
  • 0 in reply to Orlando Grigoriadi
    TI__Genius 11020 points

    Hello Orlando,

     

    Please send me an email. I have and Excel calculator for defining the LED current in hybrid mode I could share with you.

     

    Thanks.

    Best Regards,

    Tomi Koskela

    tomi.koskela@ti.com

  • 0 in reply to Tomi Koskela
    TI__Expert 4565 points

    Hi,

    This is what I got from Tomi. I took over the support for this device from Tomi by reorg.

    I've tried to attach the spreadsheet, but it didn't work.

    Please send me an email, and I can send the attachment to you.

    sungho.yoon@ti.com

    Thanks,

  • 0 in reply to Tomi Koskela
    Prodigy 150 points
    Hi Tomi,
    I have the same problem. Could you send the Excel calculator for defining the LED current in hybrid mode to me？
    Thank you！E-mail：siwei_li2@tianma.cn
  • 0 in reply to siwei li
    TI__Expert 4565 points

    Hi Siwei,

    I've sent the calculation spreadsheet in separate mail to you.

    Thanks,