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PTN04050C Transients in Output

Srinivas Nistala
Prodigy 80 points
Other Parts Discussed in Thread: PTN04050C

Hi,

I am new to the forum so hi everyone. 

I have been working on a project based on DC-DC converters, in which i require to get somewhere around 5v-10v adjustable output using 3.6v li-ion batteries.

For this i have choosen to use the PTN04050C modules. The thing is that the project requires very clean output if possible ripple should be within 50-80mV for 5v output. But i see strange transients in the output which are like some 400mV. 

I have connected all the capacitors correctly as recommended in the datasheet. Can anyone please point out what i am missing actually.

Thanks

  • 0
    TI__Guru**** 191445 points
    I moved your post to the power modules forum. Can you post a waveform that shows your issue?
  • 0 in reply to JohnTucker
    TI__Mastermind 38230 points

    Srinivas:

    Additional question and comments are:

    What is the  maximum output currentrequired  at 5V and 10V Vout?

    The ripple is published in the product specification with scope bandwidth 20mHz and typically measured across a 10-100uF output ceramic capacitor plus the required100uF polarized capacitor. By adding a 10uf otmaximum 100uF on the output bus will reduce  both switching noise and output ripple. The ripple data is  50mV to 120mV at 5v.

    1. . What scope bandwidth is used  to measure the output ripple)( it should be 20MHz bandwidth)? The scope probe should be a close coupling configuration with < 1cm ground clip length ( to ground termincation  ceramic capacitor)  with the  probe center conductor connected directly on the output bus at  the ceramic capacitor

    Tom

  • 0 in reply to Tom Guerin
    Prodigy 80 points

    Hi,

    I am Sorry for posting this late, had to deal with some other work.

    The scope used for checking the ripple was 200Mhz scope. The signal pin of the probe was connected directly on to the capacitor output. I had placed a 100uF tantalum chip capacitor on the output along with 0.1uF ceramic cap.

    But the problem isn't the ripple. The ripple is within the order of datasheet specs. What i am seeing is some kind of transient noise. Maybe it is transient because of the switching noise or maybe i am wrong.

    And i am seeing this noise when current drawn is only 0.7A at 5v output. The transient Vpp max value is 400-500mV, as you can see in the images.

    So to get cleaner output i had to add an inductor in series, but adds to the power loss in the system.

    So if anybody can help me in minimizing this transient it would be great.

    Thanks

    Srinivas

  • 0 in reply to Tom Guerin
    Prodigy 80 points
    I have posted the waveforms please check.
  • 0 in reply to Srinivas Nistala
    TI__Guru**** 191445 points

    What you are observing is generally known as "switching noise".  You have to be careful to accurately measure it.  You should use the "tip and ring" method directly across the output capacitor for best results.  If necessary you can consider adding some additional output capacitors, 0.1uF, 0.01uf and 0.001uF to help attenuate HF noise.

  • 0 in reply to JohnTucker
    TI__Mastermind 38230 points

    Srinivas:

    I reviewed the  switching noise , e-field , detection at 200mHz scope bandwidth and loose coupled scope probe  with long ground lead .

    I recommend for optimum scope detect  measurement method to connect across a 10µF ceramic  the scope close coupling see below  .The 10-47 uf ceramic will attenuate magnetic ripple and switching noise.

    Tom

  • 0 in reply to Tom Guerin
    Prodigy 80 points

    @ John , I had 0.1uF capacitor already added across the output, but i am not aware of the "Tip and Ring" measurement terminology.

    @Tom, My ground lead of the scope probe was nearly 5-6cm from the gnd on the module. I would check it with more close coupling this time as you have suggested.

    But i have already placed a 0.1uF cap accross the output along with a 100uF Tantalum. So should i replace the 0.1uF with 10uF ceramic?

  • 0 in reply to Srinivas Nistala
    TI__Mastermind 38230 points

    Srinivas:

    Thanks for the data.

    I recommend 10uf ceramic capacitor on Vout bus and while  utilizing  capacitor close-coupling scope method with scope bandwidth set to 20MHZ.

    Tom