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TPS65320C-Q1: Buck regulator output is not stable

te Yildirim
Prodigy 20 points
Part Number: TPS65320C-Q1

Hi,

We have a product that we use on vehicles. We intend to use the TPS65320C with our new design. We need to reduce the voltage from the car battery to 4.4V and 3.3V. There's a car battery on the Buck input(Vin pin). We want to get 4.4V at the buck regulator output. We feed LDO input with Buck output and we want to get 3.3V at the LDO regulator output.

We produced our test card and soldered the power circuit. When the input is between 7V and 11V, we can get the desired voltage(4.4V) at buck regulator output,but buck regulator output is increasing with input voltage while input is above 11V. When the input is 26V, the output goes up to 11V and is not stable. With that there is no problem at the LDO regulator output there we are getting 3.3V. But buck regulator does not work stable. We have not encountered any errors in the schematic and the PCB.

Could it cause trouble, can you help?

The schematic is here:

  • 0
    TI__Intellectual 1120 points
    Hi te Yildirim,

    I will assign your query to TPS65320 expert and we will get back to you.

    Regards,
    Juha
  • 0 in reply to Juha Karttunen
    TI__Genius 9615 points

    Hello te Yildirim,

    many thanks for bringing this to our attention.

    I looked at your schematic and a also agree that nothing stands out.

    The chosen Diode has a 3A-current rating, which is somewhat limited, but a 80A surge current. I would not consider this to be the root-cause, but still suggest to use a higher rated diode.

    Could you please share the part-number for the inductor?

    Since you refer to "output is not stable", could you please share a scope-plot showing Vin, Vout, switch-node and COMP?

    I may ask for Layout-details, but let's look at those first...

    I also noticed per the feedback-resistor (56k) sets the switching-frequency to ~1900kHz. The part has ~10% tolerance on the switching frequency accuracy, which may cause it to end up in (or close to) AM-band. If AM-band is of concern and there are no other reasons to use 1900kHz, I suggest to increase the switching frequency to >~2.1MHz.

    Best regards,

    Frank

  • 0 in reply to Frank Dehmelt
    Prodigy 20 points

    Hello Frank,

    Thank you for your interest.

    As a result of long work, we understand that the fault is caused by the solder paste used.

    Now the regulators are working properly.

    Thank you again for your interest.

    We appreciate your business.

    te