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LP8860-Q1EVM: PWM dimming usage

Valeri Pruman
Prodigy 80 points
Part Number: LP8860-Q1EVM


Hi

I am trying to use the PWM pin dimming mode via the EVM GUI. I followed the steps described in the user guide but I see no reaction from the LED board - they stay OFF. The "register" dimming does works fine.

Any suggestions?

Thanks

Valeri

  • 0
    TI__Intellectual 2180 points

    Hi Valeri,

    Seems like currently brightness control is set to Brightness Register instead of PWM Input.

    Could you try setting BRT_MODE[1:0] register to 00 (PWM input mode)? You can do this by unlocking EEPROM and writing to address 0x66.

    If using the LP8860 EVM GUI you can unlock EEPROM and select PWM input option on the LED drivers tab as shown below.

    Best,

    Salome

  • 0 in reply to Salome Ramirez Carrion
    Prodigy 80 points
    Hi
    I didn't try the direct write method, but I did tried via the GUI - exactly as you suggested - and this doesn't work. We have 2 EVMs and the same issue occurs on both, so I assume this is not hardware problem of the EVM. I also traced with scope the PWM signal from the MCU to the LP8860 and so that it does appears on the PWM pin
    May be there are some additional controls that need to be changed on the GUI?
    Thanks
    Valeri
  • 0 in reply to Valeri Pruman
    TI__Intellectual 2180 points

    Writing BRT_MODE[1:0] register should be all that is needed to change Brightness control to PWM input control.

    I apologize if this redundant, but could we double check that EEPROM write is effective before we look into what else could be causing this?
    Please check as follows:

    1. Provide VDD 3.3V, Vin 12V to EVM and Open LP8860 GUI
    2. Enable PWM Generator in Pin Control Tab (Leave Duty 0%) and press Update
    3. Set VDDIO/EN High
    4. Operation -> Read EEPROM (Check LED Drivers Tab, Brightness Register Mode should be selected)
    5. Operation -> Unlock EEPROM
    6. Select PWM input pin duty cycle control
    7. Operation -> Read EEPROM (Make sure that PMW input mode is still selected)
    8. Set non-zero Duty cycle in Pin Control Tab and press Update

    If this doesn’t work could you also check fault status? Are any faults set? Also could you double check interface jumper on EVM matches GUI selection (I2C or SPI).

    Thanks,
    Salome

  • 0 in reply to Salome Ramirez Carrion
    Prodigy 80 points

    Hi Salome

    This sequence does the job.

    Thank You

    Valeri