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TPS23754 vs TPS23756

Benjamin Mak
Intellectual 2190 points
Other Parts Discussed in Thread: TPS23754, TPS23756

Hi,

I was wondering why someone would choose the TPS23754 vs the TPS23756. What makes one better than the other? In what applications would one be better than the other.

From looking at the datasheet, I have found that the '54 has a 15V converter startup while the '56 has a 9V converter startup. Also, there are differences in terms of the bootstrap startup time, startup current, and UVLO. Also, the input voltages are different. Other than that, are there any major differences?

Thank you for your help!

Benjamin Mak

  • 0
    TI__Expert 7990 points

    The 754 las a larger hysteresis and higher minimum Vc voltage.  Its thresholds are a little like the old UCC3842.  The larger hysteresis makes it easier to get the bootstrap startup right (6.5V delta V on the bootstrap cap vs. 3.5V).  The turnoff min is around 8.1V - and sets the minimum switcher gate drive voltage.  The '756 was intended for applications that wanted to use a 12V adapter.  Design of a wide-range converter like that is generally more difficult, larger, and less efficient and is not necessary for many applications.  The minimum gate drive voltage will be more like 5.4V, meaning that the MOSFET Id vs Vg needs to be checked.

    The other spec differences are all a result of the lower thresholds.  Startup time is shorter with the same cap as it charges to a lower voltage, startup current for the '756 is lower as it is specified for a 12V source @ -10% minus a schottky diode.  In this case, the current source has "crushed" and acts more as a resistance. 

    Apart for the converter startup thresholds, the parts are identical.

    Choose the '754 unless you have a 12V adapter that you want to OR into the front-end.  Another (popular) way to handle the 12V converter is to OR it to the output which is designed for 12V.  We have an application note on the web that talks about ORing.

  • 0 in reply to Martin Patoka
    TI__Intellectual 2190 points

    Thanks for your response Martin!

  • 0 in reply to Benjamin Mak
    TI__Intellectual 2190 points

    Hi Martin,

    I have a question to follow up the previous post.

    I am bringing in 48V to the primary side of the AUX input when PoE is absent. I have a detector that turns off the powered device when the external 48VDC is available and run the access point off of the 48VDC.

    With this situation in mind, which device would better suit the situation?

    Thanks,

    Ben

  • 0 in reply to Benjamin Mak
    TI__Expert 7990 points

    Your situation is unclear.  The advice is still the same - while either part would work with a 48V source, you are a little better off with the '754.