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TPS82740A: Electrical Characteristics

Morrigan Aensland
Prodigy 110 points
Part Number: TPS82740A

Hello, 

I have some questions about the electrical characteristics of TPS82740A.

1. On data sheet  page 6, there has a parameter call "DC output voltage load regulation" of Vvout.

    Is this parameter for the output voltage specification of the "LOAD" pin? or for the Vout?

    What is the meaning of these parameter?

    If "LOAD" pin is not used (CTRL = Gnd),  I don't need to consider this parameter?

2. Are the figure 12~15 on page 8 & 9 showing the characteristic of "Output voltage accuracy" of Vvout parameter?

Thank you. 

  • 0
    TI__Guru*** 146060 points

    Hi Morrigan,

    The Vvout parameter is the accuracy of the output voltage of the DC/DC converter which is the VOUT pin.  The internal load switch just connects that VOUT voltage to the LOAD pin--the LOAD voltage will drop below the voltage at VOUT by the current times Rload.

    Figures 12 - 15 show the typical load regulation.  This is how the output voltage varies with load.  The Vvout specification on page 6 is at 2 load currents only, whereas the graph shows all load currents.

  • 0 in reply to Chris Glaser
    Prodigy 110 points

    Hi Chris,

    Thank you for your reply.

    So the parameter "DC output voltage load regulation - 0.001%/mA" is for the LOAD voltage at the LOAD pin?

    If I don't use the "LOAD" pin, I don't need to consider it, right?

    Thank you.

  • 0 in reply to Morrigan Aensland
    TI__Guru*** 146060 points

    Hi Morrigan,

    No, this is for the VOUT pin. 

    The LOAD pin is just a transistor between VOUT and LOAD.  It is a load switch.  There is no regulation of the voltage at LOAD.

  • 0 in reply to Chris Glaser
    Prodigy 110 points
    Hi Chris, Thank you for the quick reply. But then I am confused, since at the test conditions of this parameter, it mentioned CTRL = VIN. So if I don’t use the LOAD pin, (CTRL = GND) , how this parameter affect the VOUT? Let say my VOUT = 1.8V and Load current of VOUT is 100mA, my 1.8V will vary 0.1% which is not relate to LOAD pin, no matter I use it or not?
  • 0 in reply to Morrigan Aensland
    TI__Guru*** 146060 points

    Ah, thanks for clarifying.  The CTRL pin state also changes the bias current (Iq) of the device.  With more bias current (CTRL = high), the device is faster and will usually have a bit lower ripple.  Lower ripple will lead to a slightly improved load regulation--the voltage will not rise as high at light load.  This is a pretty small effect.

    To summarize: even though you don't use the load switch (LOAD pin), the CTRL pin has other effects on the device performance besides just activating the load switch.

  • 0 in reply to Chris Glaser
    Prodigy 110 points

    Hi Chris,

    Thank you for the explanation of the CTRL pin. 

    Then could you please help me to confirm my understand of this parameter,

    if the Vout = 1.8V and the load current of VOUT is 100mA, then the 1.8V will vary 0.1%, is it right? 

    Thank you.

  • 0 in reply to Morrigan Aensland
    TI__Guru*** 146060 points

    Well, let me explain it this way.  Vout will drop by 0.1% (typical) or 1.8mV from its value at no load to its value at 100 mA.  This is the load regulation component.

    You still have the overall accuracy of Vout at 100 mA, which is +/- 2% from the row above.  So, at 100 mA load, Vout should be between 1.8348V and 1.7622V.

  • 0 in reply to Chris Glaser
    Prodigy 110 points

    Hi Chris,

    Thank you very much, I am clear now.