• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 343 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.

USB Bus Powered Peripheral Component Selection

Nick Palladino
Prodigy 130 points
Other Parts Discussed in Thread: TPS62750

Hello,

I have a USB bus powered peripheral application that will need to charge a ultracapacitor. I need two voltages, 3.3v (~50mA) to run a microcontroller and LCD and 2.5v (~800 mA) to charge the ultracapacitor. The microcontroller will startup running within the 100 mA USB low power limit. It will then be enumerated and request 500 mA. After this, the ultracapacitor charger would be enabled to charge at the highest possible current. I'm looking for a solution that is relatively efficient, can enforce current limits for USB, and requires as little board space as possible.

I found the TPS62750 which looks promising since it has programmable current limits and is pretty efficient. I was thinking of dropping the voltage down to 3.3v, then using an LDO to get the 2.5V after that. I have seen some material explaining that LDOs are commonly placed after DC/DC circuits, but I'm not sure what considerations to make to determine the best solution for my application. I would appreciate any design guidance or recommendations for TI parts given the application I have explained.

Thank you,

-Nick

  • 0
    TI__Guru**** 150650 points

    Yes, the TP62750 is a great device to charge your supercap from USB.  I would recommend using it to directly provide the 2.5V to your supercap.

    For the 3.3V, I would run off of the USB input with the TPS62237.

    LDOs should not be needed for your design since you are powering relatively robust digital circuits and charging a super cap.

  • 0 in reply to Chris Glaser
    Prodigy 130 points

    Thanks for the quick reply! I took a look at the TPS62237. The only thing I noticed is there isn't a programmable current limit. I could just ensure that the microcontroller circuit will never draw more than ~50 mA. I'm not sure what the best practice is with respect to ensuring too much current cannot be drawn from the USB port. Is there a similar solution with a programmable current limit or do you think that would be unnecessary?

    -Nick

  • 0 in reply to Nick Palladino
    TI__Guru**** 150650 points

    This is usually unnecessary as you have control over how much current your uC draws.  

    If you're concerned about it, then you could use another TPS62750 for the 3.3V rail too.