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TPS63802: 6W LED from 2 nimh cell possible?

Kent Schafer
Prodigy 90 points
Part Number: TPS63802
Other Parts Discussed in Thread: TPS61022

I have been checking around for a driver that will power a low Vf, high power led (2A @ 3V) from 2D cell nimh batteries.  It would appear that this may be possible for Vi => 2.2V with the TPS63802? Is there a better candidate driver IC for the job?  Thank you for your help.

  • 0
    TI__Expert 7925 points

    Hi Kent,

    The TPS63802 can typically deliver up to Iout = 1.9 A at Vin = 2.2 V, Vout = 3 V, at room temperature on its EVM. In reality at elevated temperatures the maximum output current might be even lower.

    In any case, for 2S NiMH battery with a nominal voltage of 2.4 V it makes more sense to use a boost converter instead of a buck-boost. We'll check if there is a suitable boost converter. In the meantime, here you can see different ways to drive an LED using a buck-boost converter, and the same applies to a boost converter as well:

    http://www.ti.com/lit/slva419

    Best regards,
    Milos

  • 0 in reply to Milos
    TI__Mastermind 46905 points

    Hi Kent,

    you could use TPS61022 to drive the LEDs if the input voltage is always lower than VOUT. the method to control the FB voltage can be found in the application note that Milos suggested.

  • 0 in reply to Jasper Li
    Prodigy 90 points

    Thanks for the info and suggestions.  I like the appnote on the various ways to set the feedback loop for the tps63xxx devices.  I found the one with the OPA very interesting, could possibly do that onboard the micro.

    Things that are valued for design would be reverse input polarity protection, UVLO, very low quiescent current, dimming or PWM methods for adjusting brightness.  So if those are not onboard the driver IC, then they have to be added to the circuit.

    I looked at the TPS61022 data sheet previously, not crazy about the package size, but it does seem able to do 2A or more at 1.8V.  If someone could confirm that number in the real world, or from the EVM board?

    It looks like with these new chips, that a four layer board is required to take the heat away.  Would a 1oz, 0.5oz, 0.5oz, 1 oz stack be too skimpy?    If four layer, what would the recommended copper weight in the stack be?  Could a heavy copper weight (3oz or 4oz) two layer board work?

    Regards,

    Kent

  • 0 in reply to Kent Schafer
    TI__Mastermind 46905 points

    Hi Kent,

    2A@3V from 1.8V input is totally within the operation range of the TPS61022. for this loading, 2oz with two layer is OK for the thermal. but it may be related to the external components place and the ground panel.

  • 0 in reply to Jasper Li
    Prodigy 90 points

    Hi Jasper,

    Thank you for the input on the pcb layer stack and pcb copper weight suggestions, much appreciated.

    One last question before we can  close out the thread as solved, is there a chance at getting samples as an independent developer without a website?  Couldn't get past this point on the form.

    Thanks all for the help.

    Regards,

    Kent