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LP8863-Q1: LED backlight driver LP8863-Q1 issue

CHEN YAN
Intellectual 1430 points
Part Number: LP8863-Q1

Our customer is meeting an urgent issue about LP8863-Q1, they have produced 20pcs to driver LED screen, and find 5pcs screens is dim, and the brightness is non-uniform.

1.The LED Dimming mode is PWM, max current is set as 102mA, PWM duty cycle is 85%, and one device driving 4 channels of LED, leaving 2 channels idle. When testing the voltage of driving pins, LED0 is 3.64V(square waveform), and other 3 LED pins is 10V, and the normal boost output is 24V, so LED1, LED2, LED3 is not normally working, then taking apart the shell of load LEDs, and find only one LED is lighted.

2. Lighting this abnormal LEDs device in another testing equipment, the equipment is op + transistor to produce a constant-current source, and put the LEDs series of constant-current source, the testing result is 4 channels of LED is all lighted, but one channel’s current is slowly rising to current configed.

About the testing results, our customer want to know if there is a special protection method in each channel of LED, and the reason of 1 abnormal LED channel leading to the other 3 LED channels abnormal.

  • 0
    TI__Expert 5475 points
    Hello,

    Sorry the description is not that clear so I cannot understand your question clearly. Let me try to understand the issue.

    1.The LED Dimming mode is PWM, max current is set as 102mA, PWM duty cycle is 85%, and one device driving 4 channels of LED, leaving 2 channels idle. When testing the voltage of driving pins, LED0 is 3.64V(square waveform), and other 3 LED pins is 10V, and the normal boost output is 24V, so LED1, LED2, LED3 is not normally working, then taking apart the shell of load LEDs, and find only one LED is lighted.

    When you say other 3 LED strings is 10V, do you mean it is a constant DC voltage that is at 10V? Do you mean only the LED string at CH1 is lighted?
    It is better if you can share the waveform to help us understand the question.

    2. Lighting this abnormal LEDs device in another testing equipment, the equipment is op + transistor to produce a constant-current source, and put the LEDs series of constant-current source, the testing result is 4 channels of LED is all lighted, but one channel’s current is slowly rising to current configured.

    Does this paragraph mean that 4 LED strings are different? One of the LED strings is turned on slower than the other 3 strings? But you said that 5 out of 20 screens have the issue. So LED of all the 5 failed screens have the same issue?

    It is quite difficult for us to figure out the reason with your description above. Would you mind providing more details about that? And it's better if you can share the schematic as well. Thanks.
  • 0 in reply to Shirley He
    TI__Intellectual 1430 points

    Hi, Shirley,

    The schematic is as following:

    They tested LEDA and LEDK in LED series, 7 LEDs per series, and the following waveforms are one series is lighting, the other three series is not lighting.

    They want to known the reason why LP8863-Q1 can just light up one series, and what's the protection method behind? Is the impedance among these series? and how to eliminate this protection method?


    1. LEDA voltage of normal lighting series while working.

    2. LEDK voltage of normal lighting series while working.

    3. LEDK voltage of normal lighting series while starting up.

    4. LEDK voltage of abnormal non-lighting series while starting up.

    5. LEDA and LEDK voltage of normal lighting series while starting up.

    Best Regards.

  • 0 in reply to CHEN YAN
    TI__Expert 5475 points

    Hi,

    Thanks for the information. I'll close this thread since this is already solved by phone. You can open this thread if you still have any further questions. Thanks.