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3V to 12V boost with output protection?

Barry Klein1
Intellectual 610 points
Other Parts Discussed in Thread: TPS61081, TPS61085, TPS61178

I am looking for an integrated solution for a 3V to 12V boost converter with output current protection. I don't find one - probably due to the inherent architecture of boost converters. It would be conceivable to integrate OC protection into such an IC - but would require a series FET switch.

My application is using a lithium polymer 3500-4500mA range battery. Output current for this immediate application would be </=200mA. Input current from the battery is presently not limited or protected - except by the traditional battery pack protection we commonly see. I see protection devices that would handle OC and surge for the input side as well as power switches that would handle the output side. Which is commonly implemented in today's power bank products? Please realize that people may think to connect the 12V output to their car battery... (dead or being charged to ~13.8V)

  • 0
    Intellectual 610 points

    I stumbled across a part that should work: TPS61081.

  • 0
    TI__Mastermind 40080 points

    Hi,

    TPS61081 has a limit on the total output capacitance, when Cout>30uF, it will has start-up issue.  So Please make sure the total output capacitance is a small as possible.

    Generally, in power bank application, the customer will add a MOSFET and a sense resistor(20m ohm-50m ohm) in the output Return side.

  • 0 in reply to Helen chen
    Intellectual 610 points
    Oh bummer. As we would have no control over the capacitance a customer may attach it sounds like we can't use this part then - or is this a common fault with most boost converters and they must start in no load condition? What is the most common use of this port? Seems like just a bad idea to start with.
  • 0 in reply to Barry Klein1
    Intellectual 610 points
    Another thing I thought of - is it capacitance or low ESR that causes the issue? I don't see how the part can be useful with a fault like this. TI respond please!
  • 0 in reply to Barry Klein1
    TI__Mastermind 40080 points

    Barry,

     

    The IC will enter into the short circuit protection during start-up if the output capacitance is too big, because when Co is too big, Vo<(Vin-1.4V) after IC is enabled for 2ms(1.7ms minmum).

    You can refer to the datasheet for the detailed information.

     

    This is” not” a common fault with most boost converters.

     

    I suggest you to use TPS61085 and add a series MOSFET at the output return in case of short circuit condition.

     

     

    Thanks!

     

    Best regards,

    Helen

  • 0 in reply to Barry Klein1
    TI__Mastermind 40080 points

    TPS61085 doesn’t has this limitation, it can startup with load on and use much bigger output capacitance.

    TPS61081 can be used for the small output capacitance condition, some customer only add 4.7-10uF cap totally at the output side.

  • 0 in reply to Helen chen
    Intellectual 610 points
    Thanks Helen - sounds like a plan.
  • 0 in reply to Helen chen
    Intellectual 610 points

    It looks like it would be worthwhile to get an 081 eval board. I have a competitor's eval board of a similar chip as the 85.  About 78% efficiency 200mA 12Vout 3.0Vin.

    1.02A current from Vin.  One problem with it is idle current of the chip/circuit - seems 60-90mA depending on EN pin state.  The 81 seems to indicate uA currents if disabled - is this accurate?  If it truly does this it would be great as we cannot afford a 60mA load on the battery full time.  On top of this are the pluses of all the protections the 081 has that a single fet circuit wouldn't.  The body diode of the fet would let higher voltages pass (say the customer connects to a car battery...).  Like you say perhaps customer input capacitances are low?  We don't really know what the use cases are here.  Charging a GPS or handheld transceiver?  The competitor's eval board runs pretty cool at 500mA or less 12V out.  The graphs on the TI parts look like things get risky - but all we are asked to do is 200mA. It may fail to power some target applications but may be a safer design in general than an alternative.(?)

  • 0 in reply to Barry Klein1
    TI__Mastermind 40080 points

    Ctotal=Co+Cin(from the load board) You can get the total output capacitance from the customer side,  I think they will tell the data to you. and you must get this data before design. Or the time will be waste. 

    We have a new product TPS61178 which is also fit for  your application, but it will be released next year. Maybe the time is too long for you!

  • 0 in reply to Barry Klein1
    TI__Mastermind 40080 points

    By the way, could you please send the detailed application to me? like in what kind of equipment? and what is the start-up current?  You can send it to me by email:

    helen-chen@ti.com