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About common Vout line of LM3492

Guru 19475 points
Other Parts Discussed in Thread: LM3492
Customer is evaluating below ciecuit.

・LED is 4 string, Anode (Vout) ×2 and Cathode (Iout) ×4.
・In the J20 connector, two Anode lines are connected inside of connector.   
・LED driving only one of a pair.
 
Customer want to make both LED channel take a drive.

Is there a good way?

[Additional information]
・LED spec is below attached
LCD_spec.pdf
・Vout:55.8V
・Iout:85mA/string
・100% dimming
Best regards,
Satoshi
  • I'm not sure I understand the question. Do you want to use a single converter and drive only cathodes Ax or cathodes Bx depending on the panels? Or could you clarify what it is you are trying to do? Thanks.
  • Clinton Jensen-san

    Thank you for reply.
    And sorry for unclear information.

    Customer using LM3492×2, and want to normally drive anode A & B.
    But one of the pair can't drive.

    Please let me know about measure.
    (Add IC, change external components, etc)

    Best regards,
    Satoshi
  • The designs look the same and it looks like the loads are also the same. So if one is not working while the other one is either it is not enabled, there is a cold (or missing) solder joint somewhere, or the IC could have been damaged by ESD or something else. Check the enable signal first, if it is good then check all solder joints including the IC pins and DAP (the DAP is a common issue as they can be hard to solder down). Also check the connections in the connector and whatever cabling you are using, including the connection to the LED load on the other end. If all that is solid then make sure the diode isn't blown or the inductor open. If all other components are good and the solder joints/connections are good then try replacing the IC.

  • Clinton Jensen-san

    Thank you for reply.

    I checked your question, please see below.

    ------------------------------------------------------

    ①So if one is not working while the other one is either it is not enabled,
     there is a cold (or missing) solder joint somewhere, or the IC could have been
     damaged by ESD or something else.
    ⇒Customer checked and didn't find missing of solder/joint/connector.

    ②Check the enable signal first, if it is good then check all solder joints including
     the IC pins and DAP (the DAP is a common issue as they can be hard to solder down).
    ⇒These Enable is always ON(5V).

    ③If all other components are good and the solder joints/connections are good
     then try replacing the IC.
    ⇒Customer evaluating 5 unit, also occur this operation.
     Only 1 unit, by turns oscillation.(Please see below waveform)

    For reference, the other waveform is attached.

    ・U12 Cathode

    ・U15 Cathode

    ------------------------------------------------------

    If you find measure or check point, please let me know.

    Best regards,
    Satoshi

  • Could you let me know what the LED string forward voltage is for each converter and each IOUTx?