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The operation in short condition for LM3492HC

Atsushi Yamauchi
Genius 4810 points

I would like to confirm the operation in the case of "short".

I LED: 56mA (each line)

LED:  5series, Vout (for LED) = about 17V (VF = 3.4V)

In this case, the short occured in one line and Vout changed from 17V to 24V.

Is this correct operation?

And could you please teach the operation of one line for another line shorts?

Best regards,

Atsushi Yamauchi  

 

 

  • 0
    TI__Mastermind 25500 points
    Without a schematic and scope shots of Vout and the LED current it is difficult to be certain exactly what is happening, but the short answer is yes it could operate that way when an LED string is shorted. It will still try to regulate current in that channel and if it isn't able to at the lower output voltage the DHC will increase the output voltage to try and compensate, possibly all the way up to the OVP threshold of your design. This is the case for both channels shorting or one shorting. If the IOUTx pin exceeds 24V the current will begin to foldback as described in the datasheet, but the channels will still try to regulate until they are told to shut down.
  • 0 in reply to Clinton Jensen
    Genius 4810 points

    Dear Clinton-san,

    Thank you for your reply.

    I'm sorry I can not open the detail information, because it is the customer's information.

    I understood your answer.

    And i have additional question.

    I the same condition and "open" was occurred, Vout became about 25V.

    Could you please teach the operation of one line for another line opens?

    Best regards,

    Atsushi Yamauchi

  • 0 in reply to Atsushi Yamauchi
    TI__Mastermind 25500 points
    I believe the answer is similar. If one line opens the DHC control will think it needs to bring up the output voltage to a higher level to get that channel to regulation. In that case you would again likely hit the OVP level. These conditions are part of the reason OVP is a feature in the device. The idea is that it will protect everything, report the problem, and then a command could be sent to disable that channel if desired.