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TPS61165: Most Cost Effective LED Driver IC

John Deaton
Intellectual 385 points
Part Number: TPS61165
Other Parts Discussed in Thread: TPS61500, , TPS61169

Hi All,

I'm looking to find the most cost effective LED driver IC for my application.  I was looking at the TPS61165.  However, the maximum current is a little bit less than what I need (1.2 A).  The TPS61500 would work, but the maximum current is a lot higher than I need (3 A).  I'm hoping there is something in between that would be cheaper.  Here are the specifics of my application.

Output voltage - 33 V

Output Current - 100 mA

Input voltage - It has two power sources.  One is a lithium ion battery operating between 3V and 4.2V.  The other is 18V generated from an offline AC/DC converter.  

Input current - 1.375 A

I assumed 80% effeciency at the worst case of 3V for my input current requirement.

Thanks,

John

  • 0
    TI__Prodigy 600 points
    This Tread has been assigned and will be addressed in an short period of time.
  • 0
    TI__Expert 4550 points

    Hi John,

    The conversion ration fron 3V~4.2 to 33V is too high and the duty cycle may exceed the max duty cycle of the device, could you use 18V as boost input voltage? Then the inductor current is much smaller and TPS61165 could be used. If you use the lithium ion battery, the input current is 1.375A but the inductor peak current will be much higer , could be over 1.5A, so TPS61500 is not that big as you think.

  • 0 in reply to Caryss Li
    Intellectual 385 points

    Hi Caryss Li (4872533) ,

    Thank you for the reply.  To answer your question...

    Caryss Li said:

    The conversion ration fron 3V~4.2 to 33V is too high and the duty cycle may exceed the max duty cycle of the device, could you use 18V as boost input voltage? 

    I didn't explain my power source well.  I cannot use 18V all the time.  When the A/C voltage is not applied to the unit, it has to run off the battery.  So, it has to be one source or the other.  That is the reason that I had to immediately disregard a part like TPS61169 that does not have a high enough maximum input voltage.

    Concerning your statement "the duty cycle may exceed the max duty cycle", it seems that I have missed a critical specification of the part.  I understand now that only meeting the input current requirement is not enough.  Thanks for this information.  I am going to do some more research on this over the next few days.  

  • 0 in reply to John Deaton
    TI__Expert 4550 points
    Hi John,
    Good to know that, if you have further questions, please let me know.
  • 0 in reply to Caryss Li
    Intellectual 385 points

    Hi Caryss Li (4872533) ,

    You mentioned earlier in this post that the TPS61500 might not be good enough either.  From my calculations for maximum output current, it seems that it would be good enough.  My assumptions were...

    Inductance = 10 uH, Schottky Forward Voltage = 0.2 V, Switching Frequency = 1.2 MHz, Vin = 3, Vout = 33 V, Current Limit = 3 A, Efficiency = 80%

    The equations yielded a peak current of ~ 227 mA and maximum output current of ~ 210 mA.  

    I only need 120 mA out.  Am I missing something else?

    Thanks for your help,

    John

  • 0 in reply to John Deaton
    TI__Expert 4550 points
    Hi John,
    My concern is the convertion ratio, from 3V to 33V will need duty cycle higher than 91%, that will be the limitation.
  • 0 in reply to Caryss Li
    Intellectual 385 points

    Hi Caryss,

    Got it.  Thanks.  We have the option of putting fewer series LEDs in more parallel strings to lower the voltage.  Of course the current will go up so it might not work anyway.  I'm going to redo the calculations to see if we can make it work that way.  Thanks again for your help.

    Regards,

    John