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Power measurements and testing Voltmeter DVM  ---R&S RTM3K Oscilloscope Road-Test Review

snidhi

 

Power measurements and testing Voltmeter DVM

This blog is in continuation from the Rohde & Schwarz Oscilloscope Kit RTM3K-COM4 - Review

 

Here I setup an experiment to measure the ripple and do power analysis of the DC/DC TPSM84A21 Power Module. It is an integrated power solution that combines the TPS54A21, a 10-A, DC/DC, synchronous, step-down converter with power MOSFETs, shielded inductors, input and output capacitors, and passives into a package. The tests were done with 10V and 12V input voltage and outputs in the range of 0.6V, 0.8V,1V, 1.1V, 1.2V were measured.

Datasheet TPSM84A21 Power Module

 

A detailed description of the TI SWIFTTm Power Module EVM can be seen here. I will focus on the measurements with the R&S RTM 3004 Oscilloscope.

 

Power measurements in the RTM 3004

 

Fig: How to Set up the RTM 3004 for Power Measurements

 

The R&S RTM K31 Power Analysis bundle offers different options to measure input and output of (Switched Mode Power Supplies) SMPS and DC/DC Converters. The TPSM84A21 Power Module is a high current DC/DC converter. The power analysis of the DC/DC converter is presented below.

 

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Fig: R&S RTM K31 Power Analysis bundle offers

Setup of the TPSM84A21 Power Module

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Fig: Test setup for the Power Measurements

 

Measurements with the TPSM84A21 Power Module

 

The below measurements were done using the automated power analysis tool in the RTM 3004 with the DC/DC TPSM84A21 Power Module.

 

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The aim is only to present how this automated button of power noise ripple works and the below mentioned tests were done with no load in the DC/DC converter output.

 

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Fig: Power Analysis of the 0.6V output of the DC/DC TPSM84A21 Power Module

 

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Fig: Power Analysis of the 0.8V output of the DC/DC TPSM84A21 Power Module

 

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Fig: Power Analysis of the 1V output of the DC/DC TPSM84A21 Power Module

 

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Fig: Power Analysis of the 1.2V output of the DC/DC Converter Module

 

Fig: Power Analysis of the DC/DC Converter

 

The tests here will be done with fixed resistance load in the DC/DC converter output.

 

tbd.. new addition of test on popular demand

 

Spectrum analysis of the Output voltage

 

The settings to measure are as below. The Vin = 12V and Vout = 0.8V of the DC/DC TPSM84A21 Power Module. The frequency measured of the output signal is as measured above is 2MHz

 

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Fig: Settings for spectrum analysis

 

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Fig: The spectrum output for Vout = 0.8V

 

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Fig: Detailed look into the measured data

 

The minimum horizontal measurement setting for RTM 3004 is 8MHz hence the spectrum behavior immediately after the switching of the device cannot be analyzed here as it is around 2MHz.

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Fig: Detailed look into the measured data

 

Transient Analysis of the Output voltage

 

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Fig: Measuring the transient response on the output signal for Vout = 0.6V

 

Measuring with Digital Voltmeter in RTM 3004

 

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Fig: DVM features of RTM 3004

 

Below, the DVM can be seen live in action and measuring the input signal voltage of the DC/DC TPSM84A21 Power Module.

 

Fig: Measuring with the DVM in RTM 3004

 

 

In conclusion the power measurement features of the RTM 3004 are quite powerful & allows results to be obtained with minimum effort. By one click of the button the scope settings are done and one can do fast measurements instead of investing time for finding the correct settings for the tests.

  • Hi,

    Fantastic! This is one of the best review I've seen.

    I've bookmarked all your parts of your review.

    Thanks

     

    Best Regards

    Gerald

    ---

  • in reply to jc2048

    hi Jon

      wrote:

     

    With the transient test, what was the transient that you were measuring? Did you have a switched load on the output? The results look much too good to me (although a 4MHz converter is going to be fast, you wouldn't expect the control loop to recover things that quickly - a rough 'rule of thumb' is that the control loop bandwidth might be something like a tenth to a twentieth of the switching frequency). Or were you just showing us how the measurement might work by simply letting it measure the rise time of the ripple?

     

     

    To answer the last question, yes the values are too good to be true indeed and that cannot be. As in my last roadtest with this DC DC Converter module I have power ripple in mV range so they cannot go down to uV range just because the scope changed. I went back and checked my test setup again and also my last road-test as well.

    And yes my aim was only to show how this automated button of power noise ripple works but I should mention it clearly in my blog that this test was done at no load which is also not the best idea. Thanks for pointing that out.

     

    And I will re-test the DC DC board with some loads this week as I am also curious to see if I will get any better results than my Rigol scope and what is the difference in the measurement with both the scopes.

     

    Cheers image

  • in reply to DAB

    yeaa; until quite some ago.. me too doing tests by hand

    but no more

    image

    My Happy dance image

  • I remember having to do all of those measurements by hand.

     

    These new scopes are very powerful.

     

    DAB

  • in reply to jc2048

    Hi Jon,

      wrote:

     

    A couple of questions for you.

     

    I don't know much about spectrum analysers (never having used one), but don't you need to set a RBW of much lower than 4MHz to pick out a 4MHz fundamental and its harmonics sensibly? The RBW defines the resolution, doesn't it?

     

    yes indeed; hence I have mentioned it already in the blog below the spectrum analyzer measurements that the scope horizontal settings cannot be set below 8MHz on the minimum side RBW. I would have also liked it better if I could goto at-least 1 MHz on the lower side but thats not possible here.

     

    Reference in this blog:

    The minimum horizontal measurement setting for RTM 3004 is 8MHz hence the spectrum behavior immediately after the switching of the device cannot be analyzed here as it is around 2MHz.

     

    When seen at the power analysis spectrum values measured this can be set to lower frequencies. I have the results were I set it to 500KHz and 1MHz as well and did measurements but I did not publish it here but may be I should publish it as well as you look interested to see the values.

    I will publish it.