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TPS5430: TPS5430

Marco de Oliveira
Prodigy 50 points
Part Number: TPS5430 
Hello everybody.

I developed a product with a microcontroller that uses a DC-DC with the TPS5430 for a company that manufactured 80 units.
Everything is working fine until randomly some data does not arrive or is corrupted in the MCU's serial inputs.
Well, on the workbench I am able to simulate the problem and I´ve found that when the failure occurs, the TPS5430 appears
with a ripple of 160mV and the working frequency jumps from 490KHz to 510KHz.
Below you can see the captured waveforms. As I don't know the part number of the BOOT capacitor that was used, I'm suspecting it.
What do you think?

At BOOT capacitor OK 
 
NOK
 
At PH pin OK
 
NOK
 
5V OK
 
NOK
 
Schematic
 
Top copper
 
Without zone
 


PS: the L3 coil is over dimensioned indeed.

Thanks in advance

Marco

  • 0
    TI__Mastermind 35210 points

    Hello Marco,

    Sorry to hear about your issue. One of my colleagues will respond to you with their advice, shortly.

  • 0
    TI__Mastermind 24115 points

    Hi Marco,

    Thank you for sharing your schematic and layout. However it looks like there are some missing components from your schematic that are present in your layout (for example CIN is absent from the schematic but present as C14 and C12). Please share with us an updated schematic so that we may better assist you.

    In regards to your layout, I noticed that these planes look unconnected. Is there no topside ground plane connection between the ground plane above the IC and below the IC? There should be a topside ground plane that is directly underneath the IC to connect these two GND planes. 

    It would also help to move C14 in such a way where C12 can be rotated to connect to the IC's ground plane as opposed to through VIAs. This would aid in minimizing the loop created by the bypass capacitors, the VIN pin, and the TPS543x ground pin. Please see section 7.4.1 of the datasheet for more details. 

    Thank you,

    Joshua Austria

  • 0 in reply to Joshua Austria
    Prodigy 50 points

    Hi Joshua and thanks for your rapid answer.

    Here is the 24V schematic. This board will work at a battery level.

    CAD software was with 3D component enabled. Sorry for that misinformation. Here is another picture. Yes, it has zone on top copper applied.

    As to rotate the C14 capacitor. You mean this:

    Unfortunately the problem remains. You have another tips with the new information I gave to you?

    Thanks.

    Marco

  • 0 in reply to Marco de Oliveira
    TI__Mastermind 24115 points

    Hi Marco,

    Thank you for trying that. It can be difficult to determine what is causing the issue or whether the TPS5430 is causing the MCU issue at all. Is there a potential way to isolate the circuit so we can observe its behavior under normal loading conditions?

    On the other hand, I will note that per the electrical characteristics of the device, switching frequency can be anywhere from 400 kHz to 600 kHz.

     

    In terms of peak to peak ripple on output, this can be determined by any number of factors including drops in input voltage and capacitor ESR. You can find more about this in section 7.2.1.2.4 to 7.2.1.2.4.2 in the datasheet. Please check your components with these equations to make sure they are in line with the values that you desire for peak to peak output ripple.

    If you would like, you can send over your input/output conditions and the components that you used for the design, and we can run a webench simulation to check for instability. 

    Thank you,

    Joshua Austria

  • 0 in reply to Joshua Austria
    Prodigy 50 points

    Hi Joshua.

    Thanks for pointing out the frequency range, I had missed it. 
    I've already used the TPS5430 in other equipment, including in the initial
    tests I used a DC-DC module with the TPS5430, one of those you can buy on
    ebay. I can say that I'm 90% sure that the problem is ripple because when
    applying a stabilized 5V supply to the MCU circuit it works well, I left it
    running for 4 uninterrupted hours.

    OK, as this is not a commercial product, being for internal use only within
    the company site and also not being a critical product, my solution is not
    the best in technical terms, but now that the 80 boards are manufactured,
    I realized that The simplest and easiest thing would be to increase the
    output voltage a little and with the help of a trimpot I came to the
    conclusion that a 3K resistor (R3 3.24 KOhm) I can obtain 5.27V
    
After more than 4 hours of testing I had no more problems with the MCU.
    So I will close this topic.

    Thank you very much.

    Marco