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TPS54040A: Current Limit & Temp Spec

Hayden_Hast
Intellectual 1515 points
Part Number: TPS54040A
Other Parts Discussed in Thread: LM5001, LM3488, LM3481, TPS54140A

Hi Team,

I'm currently looking at using the TPS54040A for a Buck-Boost application with the following parameters:

Vin: 13 - 17V

Vout: 15V +/- 5%

Vripple: 150mVp-p

Iout Max: 250mA

However, there is no Max current limit threshold in the datasheet - only 0.94A typical. Is this an error in the datasheet? Is there data on what the max current limit would be?

Also, my application with be running in high temp environments and I was wondering if there is any data how the current limit varies over temp  (preferable from -40 to 150C)  since it is only speced at Tj = 25C.

Thanks,
Hayden

  • 0
    TI__Guru**** 191445 points

    TPS54040A is buck converter only.  It is not suitable for a buck boost.  If you were using it as a buck, the minimum current limit would be the limiting specification anyway.  I would probably look at LM3488, LM3481 or LM5001 for your application.

  • 0 in reply to JohnTucker
    TI__Intellectual 1515 points
    Hi John,

    Thanks for the quick feedback here.

    I was hoping you could help me understand the use of the TPS54040A in PMP11791 Inverting Buck-Boost design. Is there a special configuration they use in this design that makes it possible to use the buck only TPS54040A?

    Regards,
    Hayden
  • 0 in reply to Hayden_Hast
    TI__Guru**** 191445 points
    Yes, TPS54040A will operate as an inverting buck-boost. That also is a separate topology from a buck boost. To summarize:
    buck = higher positive Vin to lower positive Vout
    inverting buck-boost = positive Vin to negative Vout
    buck boost Vin min < Vout < Vin max. May operate in either buck or boost mode.

    For Vin = 13 to 17 V and Vout = 15 V, that application falls into the "buck-boost" topology.

    If you need information on the inverting buck-boost, you could start here:
    www.ti.com/.../slva257

    Let me know if this helps.
  • 0 in reply to JohnTucker
    TI__Intellectual 1515 points
    John,

    I apologize for the miscommunication, the customer is trying to achieve -15V, hence the inverting buck-boost topology. I forgot the '-' sign in the original post.

    I'll read through SLVA257, but in the meantime - will we be able to answer the following:
    - Max Current Limit
    - Max Current Limit adjustment across temp

    Regards,
    Hayden
  • 0 in reply to Hayden_Hast
    TI__Guru**** 191445 points
    Then that series of devices should work well. Since the current peak current is greater than the load current by a factor of 1-D you may need TPS54140A Rather than TPS54040A.

    There is a calculator here:
    www.ti.com/.../swiftinv-calc

    We (TI) may have some additional data on current limit. I do not directly support those devices though.