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LP8557IEVM: LEDs not turning on. help?

Lee Davis39
Prodigy 30 points
Part Number: LP8557IEVM
Other Parts Discussed in Thread: LP8557

Hello,

I just received the LP8557 KIt and after following the simple directions the LED's are not turning on. VBOOST is just 7V and I have 9 LED per string.

I did note that when I change the Current Scale to 18mA and do a readback, it still shows the default value of 25mA (111).

Anyone have a thoughts?

The LP8557 chip marking is P41

Thank you,

Lee Davis ,

Senior Hardware Engineer,

Persistent Systems LLC

  • 0
    TI__Expert 3340 points
    HI, the engineer support this device is out this week, please expect a response next Monday or Tues. Thanks!
  • 0 in reply to Sheng Jin
    TI__Intellectual 1985 points
    Hi,

    It appear the i2c communication is not working, and we need to resolve this first. At the bottom of the GUI, you should see some information on software version and USB firmware version, what did you see on your screen?

    Try using the manual control on the right bottom corner and read back register 10, it should be 07.

    Regards
    H L
  • 0 in reply to Hak-Leong Ng
    TI__Intellectual 1985 points

    Hi,

    Besides potential I2C communication problem, some of the settings can only be modified when "Enable backlight" is unchecked; "Current Scale" and "Brightness Mode" are two of these settings. To be certain, you can use the [Readback All] button to make sure the setting is modified correctly.

    If there is no external PWM signal, you can follow the steps below to turn on the LEDS after power up.

    1. Click [Readback All] button, make sure "Enable backlight" is unchecked.
    2. Select "Brightness Hi/Lo Reg" from "Brightness Mode" combo box.
    3.Check "Enable backlight" box.
    4. Adjust the brightness using the slider or key in the value in "Brightness Addr 03 and 04"

    LED should turn on base on the brightness you set to.

    Regards
    H L

  • 0 in reply to Hak-Leong Ng
    TI__Intellectual 1985 points
    Hi,

    Are you able to turn on the LEDs with the instruction mentioned in my previous post? I am still not certain if you have i2c communication issue since you did not get back to me on the software and firmware version running on your system.

    Regards
    H L
  • 0 in reply to Hak-Leong Ng
    TI__Intellectual 1985 points
    Hi Lee,

    If you have no other questions, I will close this issue.

    Regards
    H L