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TPS7A4701-EP: Data sheet current limit discrepancy for TPS7A4701

FarronDacus
Intellectual 750 points
Part Number: TPS7A4701-EP
Other Parts Discussed in Thread: TPS7A47

The Electrical Characteristics table lists the current limit for the TPS7A4700 / 4701 as 1A minimum and 1.26A typical.  This is noted to be when intended drop is 1V and Vout drops to 90% of the programmed value.  However, Figure 11 shows the current limit to vary between 1.6 and 1.9A over temperature, for the same 1V drop from Vin to intended Vout and the same Vout reduction to 90% of intended Vout.  This is quite a significant difference, and clearly one of them is wrong.  Since the part is intended to provide up to 1A, and dropping 10% in voltage at 1A would be regarded as a failed 1A supply, it seems more likely that Figure 11 is the more correct.  However, the issue really does need clarification. 

  • 0
    TI__Mastermind 20045 points
    Hello Faron,

    Generally the graphs will show some collected data while the minimum and maximums are what we guarantee. Obviously I see the concern about 1A dropping Vout to 90% of the intended value. I will look into this and get back to you.

    Thanks,
    Kyle
  • 0 in reply to Kyle Rakos
    Intellectual 750 points

    Hello Kyle:

    Thanks for the quick response. 

    Yes, if the part can depart regulation to 90% of programmed value at 1A, it is clearly a real problem for a 1A application.  Not only is the voltage off, but being out of regulation the PSRR and noise specs will probably no longer hold either.  If can be as bad as 10% low on voltage at 1A, then even at values less than 1A it is also clearly suffering on voltage, PSRR, and noise. 

    In my case I am hoping to hold good regulation with full PSRR and noise performance to 1.2A max.  That's a worse case current load for my application, but if I cannot reliably get it, then I have to use something different than the TPS7A47/4701.  

    Thanks,

    Farron

  • 0 in reply to FarronDacus
    TI__Mastermind 20045 points
    Hello Farron,

    I'm sorry for the delay. I just wanted to let you know I am still looking into this question and will let you know as soon as I have an answer for you.

    Thanks,
    Kyle
  • 0 in reply to Kyle Rakos
    TI__Mastermind 20045 points
    Hello Farron,

    After investigation, I have found that the reason the 1A spec is listed is because under certain worst case conditions (such as high temperature, large difference between Vin and Vout, etc.) Vout could drop to 90% of nominal. However, if you stay within thermal limits a better indication of the regulation is the Overall accuracy spec which shows the +/- 3.5% tolerance from 0A to 1A. If you follow the other specs (like thermal limits) you should be able to meet this regulation spec. We will likely remove the 1A minimum spec in a future datasheet update to avoid confusion. Figure 10 will still be useful to show typical values.

    Obviously if you are trying to reliably regulate over 1A this part is not intended for that operation and you may want to look at another of our linear regulators.

    Thanks,
    Kyle
  • 0 in reply to Kyle Rakos
    Intellectual 750 points

    Hi Kyle:

    Thanks, that does partially clear it up.  But, it is still a confusing issue because the answer seems to be assuming the part is operating out of its thermal spec at the 1A limit, with no actual numbers given.  It could be made more clear if some part to part variation data were included in Figure 11 showing "typical" current output capability to exceed 1.5A even at high temp.  For example, if 99% of parts could exceed 1.2A at high temp, then I would have felt fine using it for my particular application (which is pretty low dropout and not a thermal challenge).  Without some variation data to judge just how close I am to the part's true capability, I have to go to a different part.  

    Thanks, Farron