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LM3464

Ignacio Linares
Expert 1655 points

I have a customer asking the following: 

I have been playing with the eval board you got for me, and am having issues getting it running. 

I’m trying to drive a single 12V LED @ 1A.

I replaced the current sense resistors with .22OHM resistors according to the equation given in the datasheet.

I also replaced Rfb1=10kOHM and Rfb2=2.74kOHM, this should give me a Vdhc_ready=12V…. that part appears to be correct as I see ~2.5V at the Vfb_led pin @12V in.

I have the Enable pin floating, as the datasheet indicates there is an internal pullup… I only ever see about .96V on that pin though.

In addition, the VCC pin never rises above ~2.2V.

I have tried a Vin of 12-20V with the same results. Any idea what I am doing wrong here?

  • 0
    TI__Mastermind 43610 points

    Hi Ignacio,

    If you replace the components back to what was shipped does it work? The reason I am asking is regardless, you should measure the proper voltage on the Vcc pin.

    Regards,

  • 0 in reply to JCHK
    Expert 1655 points
    My customer says the following below. It sounds like it is mostly working, but the EN pin doesn't appear to be working properly:

    Customer response:
    I believe I damaged the chip somehow. I replaced it with a new one today, and got it “sort of” working.
    Everything seems to be working, except for the enable pin. I have it floating, as the data sheet indicates that there is an internal pullup and the VCC is too high to use (Enable pin max input voltage is 5.5V, VCC is 6.3). When I touch it with my meter probe to try to read the voltage, the LED channels are enabled. Kind of strange.
    I’m going to connect it to a voltage divider off the VCC for now, but it would be nice to know why it is not working.