• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 2 answers
  • Subscribers 63 subscribers
  • Views 184 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LMZM23601: comparison of EMI performances between LMZM23601v3 and TPSM84203

Brouillet Pierre
Prodigy 10 points
Part Number: LMZM23601
Other Parts Discussed in Thread: TPSM84203,

Hello,

Context of my question : I’m developping a medical device. I will have a first AC/DC adaptator (external switching power supply) with an ouput of 24VDC as i need to power a stepper motor. I need also a DC/DC regulator to power a microcontroller and a remote control (with a small oled screen) (maximum 0.9 A globally, with almost always less than 300mA ) that has the 24VDC in input and outputs 3.3 V.

I want take care of the EMI specifications as i will have to pass some EMI tests (certainly CISPR11 class B). I don’t want to take any risk and i’m following the advice you wrote in the application note « Simplify low EMI design with power modules », that is, i’m trying to use one of your modules with integrated inductors. With the specifications i have (24V input, 3.3V output, 0.9A), i found two possibilities : LMZM23601v3 and TPSM84203.

In the datasheet of LMZM23601, the figure 8 shows the radiated EMI. It is under the level of the CISPR11 class B. It is not written clearly, but i suppose the measurements are with Quasi Peak, with 10 m of measuring distance, as the limit of CISPR11 class B drawn (30 dbuV/m and 37 dbuV/m) corresponds to these hypotheses. However, we can see on the curves that there is not a lot of margin as the radiated EMI measured is above 30 dbuV/m in the 300 MHz range and in the 500 MHz range.

If we look at the TPSM84203 datasheet, the figure 25 shows that the radiated emissions of the TPSM8403 is under a CISPR (which number ?) classe B at 10 meters (with the same values as before i.e. 30 dbuV/m and 37 dbuV/m). I suppose that the measurements are also with Quasi Peak, with 10 m of measuring distance. This time, for this module, the radiated emissions are much below (below 20 30 dbuV/m until 500 MHz).

The only difference for the boards used for the measurements is that the TPSM840203 EVM has more capacitors around the TPSM84203 (but no inductance).

So my conclusion would be that the TPSM84203 has a much better EMI behavior than the LMZM23601.

However, when i use the WEBENCH tool :

  • If i don’t check the button « add en input EMI filter » with the selection « CISPR 22 class B » : the two modules LMZM23601 and TPSM84203 are proposed.
  • But if i check button « add en input EMI filter » with the selection « CISPR 22 class B » : the LMZM23601v3 is proposed but not the TPSM84203.

I don’t understand why the TPSM84203 is not proposed in the second case as it seems to have better EMI performance (see above what i said about the datasheets). Is there something i didn’t understand ? Which modules is better to use for low EMI performances ?

Second small question unrelated with the previous one : the LMZM23601v3 is almost not available in the 4 majors electronic suppliers i know. I would have to wait for May 2022 before having those modules. I would like to know if it is temporary and due to the current worldwide shortage of electronics components or if it is a problem i can have often with this component.

Thank you in advance for your answer

Best regards

  • 0
    TI__Mastermind 29690 points

    Hello Brouillet,

    I will need to understand on my end why webench does away with part selections. If I had to guess, it is based on TI product suggestion and not always necessarily 100% performance driven.

    I believe  TPSM84203 and LMZM23601 would be appreciable for your application. LMZM23601 spread spectrum is pseudo-random, so its EMC performance will tend to be better than TPSM84203 at higher frequencies (100MHZ), in addition to having a better package and pinout. My assumption for the difference in EMC performance is the quality of layout for the PCB boards utilized in the measurements.

    The latest device from TI for low EMC which could also fit your application would be  TPSM5601R5HEXTRDAR.

    I see it has a little better availability at the distributors. As you have realized, finding distribution can be difficult these days. If I had a recommendation, sticking to the newest parts would give you the best chance in securing parts is my thinking. More customers are using them for new designs and they get through the fabs the fastest. Of course, we still produce in great quantities"older" parts.

  • 0 in reply to Marshall_Beck
    Prodigy 10 points

    Hello

    First, i want to thank you very much for your quick answer, and to apologize for the delay of mine, but after having read your answer, i had to read the documentations of TPSM5601, and some others and had to analyze the layout of the LMZM23601v3, TPSM84203 and of TPSM5601. And i wanted to be sure of my conclusions to be able to answer you properly.

    If i understand well your answer, for you :

    • LMZM23601 (with spread spectrum) shoud be better than TPSM84203 (above 100 MHz)
    • You think TPSM84203 has better EMC performances in the datasheet because of the layout of the board tested.

    I understand that EMC performances is not an easy subject depending on many factors. But i admit i was hoping to get a more precise answer.

    Especially, if you compare precisely the two curves i mentionned in my first message :

    • In the range 100 MHz and 500 MHz, the TPSM84203 is less thant 20dB compared to the LMZM23601 which reaches often 35 dB. The difference is huge (and contrary to the fact that the LMZM23601 shoud be better with spread spectrum)
    • If we read your very interesting Application « EMI Mitigation Techniques Using the LMZM23601 ». We can see than no change on the layout can improve so much (in the level of the TPSM84203 performance) the LMZM23601 EMC performances. Only the last scenario mentioned in this application note, with an input filter can reach similar performances (l<20dB until 500 MHz). And in this case, the curve looks like more the one of the TPSM84203 (« gentle » and « regular » rising slope). So because of this, i find your answer hard to believe.

    Furthermore, i analyzed the layout of the EVM boards used for the tests (it is written on the datasheet that the tests are done with the EVM board. And i did’nt notice any big difference :

    • tpsm84203 EVM. Very simple two layers PCB. Not shielded (i.e. no top and bottom ground layer to create like a shield.)
    • lmzm23601v3 EVM :  4 layers not shielded either (there are paths on the top with Vin, Vout, and GND)
    • TPSM5601 : it has performances very similar to the TPSM84203. The EVM of this board, this time is a 4 layers shielded (with full Bottom an Top Ground layers).

    I hope i have explained crearly why i’ve found your answer a bit quick and hard to believe.

    If you agree with my argumentation and you have other ideas, i would appreciate to know them.

    But as i said, i understand that predicting ECM performances is not an easy task. And so, if you have no explanation about the contradictions i mentionned, i will select one of the components on other constraints, and i will see  with the certification test if i pass or i fail.

    The TPSM5601 seems to be also a good solution. Thank you for the tip. I didn’t select i at first because it needs more parts around it. But maybe i will change my mind (i have still some difficulties to select capacitors around it because i found big differences between the values mentionned in the datasheet and what is given by the Webench tool. And i’m a little bit lost).

    Thank you again for your answers

    Regards

  • 0 in reply to Brouillet Pierre
    TI__Mastermind 29690 points

    Hello Brouillet,

    You are right in that a lot of variables come into play with the EMC performance of these devices.

    One thing that I failed to mention in addition to layout is layer count/stackup, as well dimensioning of PCB, which could potentially impact those frequency ranges.

    In general EMC performance can be impacted at IC level by  packaging, IC layout process, IC floor planning/layout, and spread spectrum technique to name a few.

    If you wanted TI's recommendation of best performing device for EMC, the latest devices (ie: TPSM5601) would often have newest process and packing design, as well, spread spectrum.

    Of course, I recommend you to consider all options and choose based on what you feel is best for your application.

    IF you need suggestions on filter design and or layout critique, let me know.

  • 0 in reply to Marshall_Beck
    Prodigy 10 points

    Hello,

    thank you again for your quick reply.

    So i understand it is not possible to have more precise clues to explain the strange differences between the different curves of the datasheet i mentionned earlier. Thus, I will choose the module that matches the best other criterions. (taking of course also into account what you said about the advantages of the TPSM5601).

    If i have some EMC test of my device, in the future, i will try to post in this discussion the results of the test to make to you and other readers,a feedback.

    Thank you again.

    Regards