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LM3410-Q1: Automotive input voltage range (up to 18vdc)

Travis Travelstead
Prodigy 70 points
Part Number: LM3410-Q1
Other Parts Discussed in Thread: LM3410


In the datasheet there is an app note on working with voltages above Vin. I only see notes on 9-14v, but it is not clear what the limits of this is and if sustained voltages up to 18v would cause issues. I like the simplicity of this LED driver but need to pull from 12v battery source in order to avoid unnecessary power conversation. Other devices are more complex than what I need so I like the idea of using the simple LM3410 as a display backlight driver. The application not below also is close to my application needs, just with 6 LEDs and running a forward voltage of about 16v.

  • 0
    TI__Mastermind 28655 points
    Hello Travis,

    That is a design example. If you are designing a boost you can do that up to the rating of the part. You could set it up for 18V input for the power stage as long as Vin is regulated below 5.5V. Also, with a boost converter, if you set up the output to be near 18V, say 20V, you will not ever be able to dim to zero current since a boost will just feed the input to the output through the boost diode. Vf of LEDs drops with current so the LEDs will remain somewhat lit at 18V - Vboost diode. This can be figured out from the LED datasheet/testing. Your design needs to stay below ABS MAX under all operating conditions to prevent damage.

    Best Regards,
  • 0 in reply to Irwin Nederbragt
    Prodigy 70 points
    Thanks for your reply, it is very helpful.

    I thought it would be fine if the boost voltage was safe up to 24v, but you did point out the other concern on making sure the output can be PWM'ed. I also should have been clearer that the IC would get regulated 3.3v.

    One of my specific use-cases is a 6-LED series with a forward voltage of about 18.6 volts needing 60ma for full brightness. The typical battery voltage should be 12-14v but with automotive you might have transient lows and highs on the 12v battery which could be in the range of 8-18vdc. The systems I work on are very stable, but I still want to plan for such transients. I was planning to put a 20-21v zener/tvs on the output for the overvoltage/transient protection.

    If you see something I am missing I would be interested in a reply. Otherwise it does sounds like this will fit my needs.
  • 0 in reply to Travis Travelstead
    TI__Mastermind 28655 points
    Hello Travis,

    Clamping with a zener/TVS at 20-21 volts will not be easy. Look at the specifications on TVS diodes and where they start conducting to how they clamp (the knee) and tolerances. I guess you'll just have to try and see how it works.

    Best Regards,