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I am designing a board that has an LCD and msp430fr2433. They both need 5v and 3.3v respectively. So I decided to use TPS560430X3FDBVR and TLV70033DSET to provide 5v and 3.3v. I have attached the schematic and traced the path with a yellow highlighter. I hope this makes it easy to follow.

I followed the circuit recommended by the datasheets of the regulators except for Cboot which is 1uF on the board. Is anything wrong with my schematic?

Problem: I connected the board to a 12V DC power supply. It's pulling 3A. Seems like there is a short but nothing is burning. Not sure why there is a 3A draw when the 5V regulator output current is 0.6A max.

I didn't find any short but the 3.3V regulator and micro pads are underneath the component. I can't see if there's a short.

Analysis: If there is nothing wrong with my schematic, I plan on concluding that there is a short. I just want to get a second opinion about the schematic.

Datasheets:

5v regulator https://www.ti.com/lit/ds/symlink/tps560430.pdf?HQS=TI-null-null-digikeymode-df-pf-null-wwe&ts=1606594508057

3.3v regulator https://www.ti.com/lit/ds/symlink/tlv700.pdf?HQS=TI-null-null-digikeymode-df-pf-null-wwe&ts=1606600030251

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1 Answer 1

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The TPS560430X3F is a fixed 3.3V model, so you are using the wrong regulator model.

It seems that what you wanted was the adjustable TPS560430XF model, i.e. "XF" instead of "X3F".

The incorrect regulator does not work in the circuit meant for adjustable model, and has damaged the rest of the components with overvoltage.

Explanation:

If read the datasheet correctly, the fixed 3.3V version has the feedback reference voltage of 3.3V instead of 1.0V, so the feedback resistors try to set the regulator output to 16.5V.

So basically the 5V node has most likely had serious overvoltage, and it's exceeded the ratings of all 5V powered components, and they are damaged. For example the 3.3 LDO has absolute maximum rating of 6V, so chances are everything powered by it is also damaged.

Edit: After changing to correct adjustable regulator component, apply the input supply with the proper polarity.

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  • \$\begingroup\$ I understand. I used a 3.3V fixed regulator and had the circuitry which was meant for an adjustable regulator. This gave 16V which might have blown the components on the other side resulting in a short. Hence it's pulling 3A, which is the maximum current that my DC power supply permits. If I replace it with the following component, the circuit would work fine? digikey.com/en/products/detail/texas-instruments/… \$\endgroup\$
    – varun
    Nov 30, 2020 at 16:35
  • \$\begingroup\$ You can check the datasheet if the part number matches what you need. \$\endgroup\$
    – Justme
    Nov 30, 2020 at 16:50
  • \$\begingroup\$ I did .. That's the one that is adjustable. The circuit around it gives 5V output. I was just double-checking .. Thanks for your answer. \$\endgroup\$
    – varun
    Nov 30, 2020 at 17:04
  • \$\begingroup\$ So I brought the correct component and soldered on a brand new board. The same thing happened. Now sure why? There's literally nothing connected after the output capacitor of the regulator. It's impossible to have a short. Seems like there is a design flaw that I can't see. Can anybody see what I can't see? \$\endgroup\$
    – varun
    Dec 10, 2020 at 0:05
  • \$\begingroup\$ So there is another issue. Can you add more info, like schematic layout and list of the components (inductors, resistors and capacitors) around the TPS560430, and photo of the board area with aforementioned parts? \$\endgroup\$
    – Justme
    Dec 10, 2020 at 5:15

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