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TPS54A24: Questions of TPS54A24

Jimmy Lai
Expert 6845 points
Part Number: TPS54A24
Other Parts Discussed in Thread: TPS566231, TPS566242, TPS568231, TPS566247, , TPS56C231

Dear Team,

Looking forward to your answer of my questions. 

And we have run some simulation on TI’s WEBENCH and found some of them not able to reach 90% efficiency. Since it is evaluating for a fanless system so the efficiency is quite important relatively.

Would you please suggest us the suitable parts for our DC/DC solution with the requirements listed below?

  1. Efficiency >90% at least.
  2. Vout tolerance must < 1%.
  3. Cost is sensitive, the cheaper the better.
  4. 12VIN
  5. Vout/Iout: 3.3V/4.199A and 0.8V/ 4.119A

Many Thanks,

Jimmy

  • 0
    TI__Mastermind 23800 points

    Hi Jimmy,

    For 3.3V, there should be many options like TPS566231/8, TPS566242/7

    For 0.8V, TPS568231 at 400kHz switching frequency looks like a good option.

    Thanks,
    Amod

  • 0 in reply to Amod Vaze
    TI__Expert 6845 points

    Hi Amod,

    After these days, I have tried and convinced our customer to loose the requirement of efficiency. Now they could accept that it is better to have >85% efficiency but >90% is no longer a hard requirement due to we show them the improvement on efficiency isn’t help thermal relief that much.

    And I have checked the solutions that you recommended. Please see my reply inline[12/13-A].

    For 3.3V, there should be many options like TPS566231/8, TPS566242/7

    [12/13-A]

    For TPS566231/8 of 3.3V/4.199A application, they are 6-A solutions and with auto-skip/continuous current mode and soft-start/power good functions respectively. For mode selection, we might choose the type of continuous mode for better stability and performance from my personal perspective. However, for soft-start/power good, I’d like to have both functions for POL. I am not sure if the TPS566238P has the internal soft-start. If it has, we may choose the P-part and have soft-start and power good functions at the same time although the soft-start is not adjustable, but still better than nothing.

    The last, I’ve run simulation via TI WEBENCH. Although the efficiency is quite good that over 92% overall but its Vout tolerance is 2% even I already changed the voltage divider tolerance to 0.1%. These POLs may not be the suitable solutions of our case.

     

    For TPS566242/7 of 3.3V/4.199A application, they are 6-A solutions and with Eco-mode/FCCM mode respectively. The same as above we may choose the one with FCCM mode. However, they have internal soft-start but don’t have power good indicator. As mentioned above, I’d like to have both. I have to make another power good circuitry for the POL if it doesn’t have PG function because we will need the indicator for proper power sequence.

    For the simulation result of TPS566247, the result is similar to TPS56623x. The efficiency is good that over 92% overall and Vout tolerance is ~1.9%. May not be the suitable solutions of our case either.

     

    For 0.8V, TPS568231 at 400kHz switching frequency looks like a good option.

    [12/13-A]

    For TPS568231 of 0.8V/4.119A application, this is an 8-A solution and with both soft-start and power good functions, which is good. It could be the suitable solution for this application. Would you please let me know which one is cheaper between TPS568231 and TPS54A24?

    But I tried to simulate from TI WEBENCH and can’t find this part from the power designer. Is there any way to check the performance like efficiency or its Vout tolerance? As I recalled, sometimes TI would provide another spreadsheet and calls it as ‘calculator’ for some POLs. Does this one have the calculator spreadsheet?

    Many Thanks,

    Jimmy

  • 0 in reply to Jimmy Lai
    TI__Mastermind 23800 points

    Hi Jimmy,

    Yes the TPS56623x has either PG or SS. Both functions are not available at the same time. TPS56624x can be used with internal SS time of 1.39ms typ with PG feature. It looks like you need a device which has both PG and SS features available. Can you share your WEBENCH design? I am not sure what their VOUT tolerance equation is but it most likely is based on worst case analysis and may not be what you always see on the bench. Vout tolerance can be a function of other variables like FB resistor tolerance, FB accuracy (1% at room temp) and also output ripple due to a certain output cap which will affect the DC voltage especially in PFM. If you are looking for even tighter accuracy, you'd need to use 0.1% tolerance FB resistors and enough output capacitance to minimize the ripple effects which can change DC accuracy in PFM. Is there a certain output ripple (mV) requirement? 

    To summarize, the requirements for 3.3V, you are looking for SS and PG features both in addition to less than 1% FB accuracy while maintaining > 85% efficiency at 4.119A. Is that correct? 

    On the TPS54A24 vs TPS568231 price, TPS568231 1ku price shows lower on ti.com. I need to find out why TPS568231 is not on WEBENCH. But, you can use TPS56C231 has it has the same FETs. Here is a link for the WEBENCH design: https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=E40A62680828D33D 

    Thanks,

    Amod