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LP3954: Current value shifts with continuous use

Kaji@PAN
Mastermind 7840 points
Part Number: LP3954


Tool/software:

Hello,

I am an FAE at a distributor of TI products, my customer has asked me about the LP3954.
The operating conditions and problem symptoms are as follows:
WLED1 and WLED5: Setting to 5mA
Assumes continuous operation for 3 hours per day for 20 days
When used for the above period in environments of 40°C and 60°C, the current value drops.
In short-term tests, the current value returns to normal when the ambient temperature reaches 25°C.
However, after 20 days of continuous operation, the current value remains low even when the ambient temperature reaches 25°C.

Is the current value still low because the IC is broken?
Or is it due to aging?
Please let me know your opinion.

Best regards,

  • 0
    TI__Expert 6610 points

    Hi Kaji,

    Before doing the judgement I have some questions below that need your help to answer.

    How much is the "low" current under 40°C and 60°C? Is the "low" current after short-term tests same as after 20 days tests?

    What's the Vout voltage and LED forward voltage?

    Are only the WLED1 to WLED5 constantly turned on under 40°C and 60°C temp without any other external conditions applied to the device?

    Best regards,

    Felix

  • 0 in reply to Felix Wang
    Mastermind 7840 points

    Thank you for your reply.
    Below is what I confirmed with my customer.

    How much is the "low" current under 40°C and 60°C? Is the "low" current after short-term tests same as after 20 days tests?
    (Answer)
    It seems that they did not actually check how much the current value changed.
    The actual phenomenon is that the LED brightness has decreased after 20 days of operation.

    What's the Vout voltage and LED forward voltage?
    (Answer)
    Vout is 4V and Vf is 3.2V.

    Are only the WLED1 to WLED5 constantly turned on under 40°C and 60°C temp without any other external conditions applied to the device?
    (Answer)
    Yes, only WLED1 to WLED5 are lit.

    Best regards,

  • 0 in reply to Kaji@PAN
    TI__Expert 6610 points

    Hi Kaji,

    Thanks for your information. 

    But could you ask customer to measure the output current and voltage on the WLEDx pin of the chip under the conditions below separately (no need to measure on the same chip)?

    1. At ambient temperature 25°C
    2. After short-term tests at 40°C and 60°C
    3. After long-term tests at 40°C and 60°C

    Besides that, could you share more information about the projects below (felix-wang@ti.com)? There may be new released device to recommend.

    1. Are only 5-channels required?
    2. Is the max current 5mA per channel?
    3. What's the input voltage range?
    4. What's the customer and end equipment?

    Best regards,

    Felix

  • 0 in reply to Felix Wang
    Mastermind 7840 points

    Thank you for your reply.
    I received the following message from my customer.
    Regarding current measurement, they are having trouble analyzing the issue because the structure of the equipment does not allow for measurements.
    Therefore, they would like me to confirm whether there is any information that suggests the current value of the IC alone fluctuates when used for long periods of time in a high temperature environment.
    If this is not a possible mechanism, that's fine.
    Best regards,

  • +1 in reply to Kaji@PAN
    TI__Expert 6610 points

    Hi Kaji,

    There should be no problem for the device working 3 hours per day for 20 days under 60°C temp. I tried to find the reliability test data of this device but couldn't find as the device was relatively old.

    And I still would like to know if you can help to answer the questions below. If there is confidential information you can send it to my email, felix-wang@ti.com .

    1. Are only 5-channels required?
    2. Is the max current 5mA per channel?
    3. What's the input voltage range?
    4. What's the customer and end equipment?

    Best regards,

    Felix