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LM3466: LM3466 COMM Output

Isee
Expert 6650 points
Part Number: LM3466

Hi Team,

my customer wants to daisy-chain the LM3466. Is it mandatory that LM3466 COMM output needs to be connected with other LM3466 devices? For their specific use-case that would be not ideal.

Regards

Andreas

  • 0
    TI__Mastermind 28655 points
    Hello Andreas,

    From the datasheet: "For proper operation of an LM3466 lighting system, the COMM pin of all LM3466 should be either shorted
    together or connected through a diode in parallel with a resistor.
    Figure 15 shows an optional circuit for the COMM pin to indicate whether each LED string is active by means of
    small signal LEDs. The COMM pin of each LM3466 is connected to an external test point COMM_ALL through
    the optional circuit."

    If you are daisy chain connecting Veq why is it you cannot daisy chain COMM? It should still work though any fault condition may cause issues with the design.

    Best Regards,
  • 0 in reply to Irwin Nederbragt
    TI__Expert 6650 points

    They have the LED drivers spread out situated on different boards

    What if the Veq are connected via longer lines, will current control then be less accurate?

    Let`s say it is not mandatory to connect COMM PIN with other drivers - an the ouput be terminated with a pull-down resistor vs. ground?

    Regards

    Andreas

  • 0 in reply to Isee
    TI__Mastermind 28655 points

    Hello Andreas,

    The resistor and capacitor on Veq are for the LM3466 control loop.  Longer lines on this connection are not recommended (define longer lines).  Also, if the LM3466s are separated with 'longer lines' how is the IC ground reference going to be maintained?  The LM3466 was meant as a current share device where they were all located on one PCB with a common ground.  I would think you could leave COMM open but if you are running Veq, power and ground why not COMM though separate LM3466 on wire harnesses doesn't sound like a good idea.

    Best Regards,