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LM3410: Using the LM3410 as two channel driver

arnon hadas0
Prodigy 60 points
Part Number: LM3410

I Would like LM3410 as two channel driver and switch between the channel externally

is it possible ?

  • 0
    TI__Mastermind 25500 points

    Hello Arnon,

    That really depends on what your LED strings look like. Will they have about the same total forward voltage? You would need to pull DIM down while you switch between the two but if the voltages are close it should work fine. If they are much different then I guess it is still technically possible. But if you switch in a lower Vf string the output capacitor will give a surge of current through the string. In both directions you will get a transient event if they are different since the internal compensation will have to react each time. Cycling the input voltage could prevent that but it will be slower.

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Prodigy 60 points

    The total forward voltage is very different 3 led vs 1

    But only one set of the leds will be on at a time

    And the off time between them can be very large (seconds)

    Were will you suggest adding the external switching ?

  • 0 in reply to arnon hadas0
    TI__Mastermind 25500 points

    Hello Arnon,

    What is the forward voltage of the LEDs you are using and the input voltage? 1 seems pretty low for a boost converter. What kind of LED current do you need and do you require PWM or analog dimming?

    In either case if the on time is low and not often and the startup time (on the order of a few ms) isn't too long you could just turn it on and off as needed. You would put an NFET between each string and the feedback pin and just enable the one you like before turn on. If it ends up you really need a buck converter they are much faster and the options improve.

    Let me know and I'd be happy to make some recommendations if needed.

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Prodigy 60 points
    The forward voltage of one set of leds is 3.2v(one led) and the other is 9.6 (three leds) current will be less then 20mA for both
    the input voltage will be 2 AA batteries so 3v-2.5v
  • 0 in reply to arnon hadas0
    TI__Mastermind 25500 points

    Hello Arnon,

    With that input voltage the LM3410 is your best choice.

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Prodigy 60 points
    will it be possible to use it in boot strap configuration with the switching?
    if you can provide schematics it could also help
  • 0 in reply to arnon hadas0
    TI__Mastermind 25500 points

    Hello Arnon,

    Could you clarify what you mean by "boot strap configuration"? Do you mean run VIN from the output voltage after startup? If so you can and it would simply be a diode from both the input voltage and the output to VIN so it runs off the higher of the two.

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Prodigy 60 points

    attached is to circuit for bootstrap configuration i wold like to use it with more leds and switching as we discussed earlier. 

  • 0 in reply to arnon hadas0
    TI__Mastermind 25500 points

    Hello Arnon,

    That is correct, mostly. Something must have happened during the last datasheet update however as there are some missing connection points in that schematic (they appear in older datasheets). Where it says "VIN" there should be a junction between VIN, D2, and C1. There also needs to be a junction between pin 2, C3, R3, and D3.

    I'm guessing they may have run some autocheck on it and the software didn't like 4 way junctions but didn't fix the connections. You still need to take into account the max VIN pin voltage and/or use a resistor and zener clamp.

    Regards,

    Clint