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TPS62933: TPS62933

Sina Ghofrani Majelan
Prodigy 10 points
Part Number: TPS62933
Other Parts Discussed in Thread: TPS563300

Tool/software:

Hello,

I have two TPS62933PDRLR regulators on my PCB to generate 3.3V and 5V from a 12V input.

The schematic and layout for both regulators are quite similar. The 5V regulator works well and generates 5V from 12V as expected. However, the 3.3V regulator is producing 3.6V instead of 3.3V. I attempted to adjust the feedback resistor to reduce the voltage, but this caused the output voltage to increase to 4V.

I also experimented with different Rt resistors to check if the issue was related to the switching frequency, but this had no effect.

Let me provide more details about the experiments I conducted, which I hope will help identify the problem.

When I powered on the board for the first time, the voltage of the power supply dropped from 12V. I increased the current limit of the power supply, and at some point, the voltage and current stabilized. Upon measuring all the voltages, I observed that the 3.3V regulator was not functioning properly.

Another peculiar observation is that when I measure the input voltage at the 3.3V regulator, specifically at the input capacitor, I read 11.6V instead of the expected 12V. I am unsure of the reason behind this drop.

I would greatly appreciate any suggestions or insights regarding the possible cause of these issues and steps to troubleshoot them.

  • 0
    TI__Mastermind 27936 points

    Hi Sina

    Can you please share your schematic and layout?

     the 3.3V regulator is producing 3.6V instead of 3.3V-----Can you please measure the voltage waveform of FB pin and SW pin?

    Another peculiar observation is that when I measure the input voltage at the 3.3V regulator, specifically at the input capacitor, I read 11.6V instead of the expected 12V. I am unsure of the reason behind this drop.-----There can be some voltage drop on the input trace.

    Thanks and best regards.

  • 0 in reply to Gui He
    Prodigy 10 points

    Hi Gui,

    Thank you so much for your reply.


    This is the scematic and Laoyout of the board:












    During this time, I conducted an additional experiment. To ensure that the 3.3V regulator was not faulty, I replaced it with another compatible part, the TPS563300 (which has the same footprint as the TPS62933), and obtained the same results as with the previous part.

    To take the experiment pictures I am about to send, I set the power supply to 12V with a current limit of 300 mA. Occasionally, during power-up, I hear a noise from the board (I guess the noise comes from the inductor, but I am not sure), and the voltage drops during that time. Afterward, the noise disappears, and the voltage and current of the power supply stabilize.

    This is the output of the 3.3V regulator:





    If we zoom on the output voltage we will see this:







    This is the FB pin:

    This is the SW pin:

    This is the BST:

    This is the input of the regulator:

    When the input voltage is greater than zero but before the rising edge in the middle of the image, the board produces noise, and the power supply voltage drops.



    Regards,
    Sina




  • 0 in reply to Sina Ghofrani Majelan
    Prodigy 10 points

    Hi Gui,

    I would like to add some information to my previous message.

    It seems that the SW pin of the regulator is not switching as expected.

    I checked the SW pin of the 5V regulator, which is working well, and it is switching, as you can see in this picture.


    I thought that perhaps increasing the capacitor between the BST and SW pins might help. So, I increased it from 0.1 µF to 0.22 µF, but I observed the same results as before.

     

  • 0 in reply to Sina Ghofrani Majelan
    Prodigy 10 points

    Gui,

    Just for your information, the part number of the inductor in 74438357047.

  • 0 in reply to Sina Ghofrani Majelan
    TI__Mastermind 27936 points

    Hi Sina

    I see that the layout has some problem and should be optimized: the FB resistors, the RFBB should be placed close to FB pin AND IC GND pin, your RFBB to GND trace is long.(I didn't see this, but should has been routed on other layer through the via according to the image). And recommend sample the Vout from the Cout + node, other than the inductor pin. 

    Thanks and best regards.