• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 681 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM3406HV: SNVA407B

Marcin Brylak
Prodigy 205 points
Part Number: LM3406HV

Dear TI Support,

I am testing AN-1993 LM3406HV Evaluation Board with 2 Wire Dimming ( SNVA407B) and it seems not to work as constant current. The current is changing with LEDs number (load) and output voltage seems to be stable which is not clear for me. If needed I can provide some screen shots from oscilloscope.

BR

Marcin

  • 0
    TI__Mastermind 25500 points

    Hello Marcin,

    Is this with the EVM as-is with no modification? Scope shots would help, but I would also like to know what your operating conditions are. What is the input voltage you are using? What is the Vf of the LEDs you are using and how many for the different configurations (output voltage range)?

    Thanks,

    Clint

  • 0 in reply to Clinton Jensen
    Prodigy 205 points
    Hello Clint,
    I used 1k Ohm load resistor for this test. Now I checked with 1 Ohm and it is working. Normally InGaN diode has rd of 0.4 Ohm so I used to large load resistor. What is the maximum load resistor which I can use for my tests?
    Thanks
    Marcin
  • 0 in reply to Marcin Brylak
    TI__Mastermind 25500 points

    Hello Marcin,

    A resistor doesn't behave at all like an LED, and an LED with an Rd of 0.4ohms is nothing like a 0.4ohm resistor and its Vf will never be ILED*Rd.

    Having said that you can still test with a resistor but you want to set the output voltage near what your LED(s) voltage will be. For example, if you are trying to emulate a single 3.5V LED at 1A of load current you would use a 3.5ohm resistor. If it's two series LEDs at 1A you would use a 7ohm resistor. As you can see this will require high power resistors. The maximum value would depend on the input voltage as ILED*R needs to be lower than VIN. This is why 1k will not work, it will just put the device into maximum duty cycle and the output voltage will just hover near the input voltage and you will never reach max current.

    Regards,

    Clint