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TPS61020: Application Report SLVA236

Part Number: TPS61020

Hi,

I want to repeat the measurements you performed at the following application note: www.ti.com/.../slva236a.pdf

I want to do it with different instruments and compare the results.

I would be interested in knowing how did you measure the voltage and currents at the input, with which instruments, and how did you calculate power both with and without the additional input capacitor. For example, did you measure average values and then multiplied them? Or did you use rms values?

Can you also tell me which additional capacitor did you use?

Regards,

Manel

  • Hi Manel:

    Actually that application note was written 12 years ago. It's hard to check the details about the equipment and part. 

    The requirement for the equipment is depend on the accuracy you need. And we will measure the average current typically, and then multiply them.

    You could choose larger than 470uF capacitance to have accuracy result.

     

  • That's true but I've seen it has been revised recently. Maybe you can ask to the author of the application report, if possible.

    From your answer, do I understand that you take the average values of voltage and current and multiply them in both cases. Don't you consider the AC rms values?

    Regards,

    Manel

  • Hi Manel:

    Sorry that the reversion is not aimed about the test, as it listed in page 8,"reversion history". And in other hand, it's not necessary to use same equipment. As I mentioned, the requirement for the equipment is depended on the accuracy you need.  

    And for your questions, that's one of reasons why we recommend the additional capacitance.  The input current is small for light load in PFM. So the large input capacitance will decrease the AC factors a lot. If you could still observe a obvious unstable test value, please add larger capacitance.

  • Hi,

    just answer my question about how you calculate power in both cases. Do you only use the average values of voltage and current? Or do you use the rms values? When adding the capacitor average values make sense but what about when not using the additional input capacitor? In this case you have a large AC current (and some AC voltage because of the voltage drop in the shunt resistor of the current meter). How do you calculate input power and thus efficiency in this case?

    Regards,

    Manel

  • Hi Manel:

    Thanks for your supplements. It's really good questions. And I didn't think about which is better without additional capacitance before. I will check with my team later .

    By the way, may I ask why you don't want to add an additional capacitance? It's easy to setup and  could get accuracy test result. Since the large capacitance will make the input current stable and no much AC factor, so there is no obvious different between average value and RMS.

  • I'm a university professor and I wanted to research a little bit about this issue in order to gain knowledge and probably generate an academic paper. For example, to know which instruments or measurement methods are appropriate with and without the additional capacitor.

    Best regards,

  • Hi Manel,

    theoretically, we need to measure the voltage and current in real time. integrate the product of the voltage and current over time, then divide the time.

    in the lab, we will add large capacitor to stabilized both the input voltage and input current. then it is easy to measure the two value using multimeter from Chroma. similar as .

    we don't have an equipment that can precisely measure signal with oscillation. also please share us if you have better solution.

  • ok. So, can I understand that you measure the DC voltage and DC current when adding the large capacitor and multiply both values?

    On the other hand, do you do the same when not adding the large capacitor (there are graphs of efficiency with and without the large capacitor)?

    Regards,

    Manel

  • Hi Manel,

    your understanding is correct. we only measure its DC value.

    without the large input capacitor, the value showing in the chroma meter would always change. this is not acceptable to us. we just want to get efficiency with acceptable accuracy. we don't try to research it.

    the graphs with and without capacitor in the application note is to tell our customer to add capacitor.

  • Thanks.

    Just a last remark. You say that with the large input capacitor values of the meter wil be changing. But, can it be possible even in this case that values remain stable (as the meter provides the average) but different that when adding the capacitor?

    Thanks for all your answers,

    Manel

  • Sorry, the correct sentence should be:

    You say that without the large input capacitor values of the meter will be changing. But, can it be possible even in this case that values remain stable (as the meter provides the average) but different that when adding the capacitor?

  • Hi Manel,

    i think it is possible if there is large oscillation in the input voltage, but filter of the meter stabilize this input signal. 

    thus, we normally also measure the ripple in VIN using oscilloscope to make sure voltage ripple is small enough.

  • Hi Jasper,

    What about the current oscillations that can be even larger than voltage? Does it applies the same?

    In the application note you also show scope graphs of the current. Did you use a current probe for that?

    Regards,

    Manel

  • Hi Manel,

    the application is not written by me. if the voltage is stable and the average input current can be measured, I think the efficiency is the same at large ripple input current or small ripple input current.