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I have attached a PSU design which I have created. The input voltage is between 12 and 24V DC.

The first stage creates an isolated output voltage of 7V that is then fed into the two TPS562208DDCT (buck converters) to produce 5V on IC3 and 3.3V on IC2.

The circuit is working as intended, without a load connected to the output. For the test, I removed IC2 and was just working with the 5V output. When I measure the output of the IC3 without a load, then the voltage is 5V as expected.

However when I connect a load that typically draws between 300mA and 550mA, the output of IC3 drops to 2.2V which seems like IC3 is current limiting. According the datasheet of the TPS562208DDCT, the chip can deliver 2A. I have followed the suggested components according to the datasheet.

Any suggestions on changes or corrections that can be made, will be highly appreciated. Thanks in advance.

schematic diagram

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    \$\begingroup\$ Can you specify the parts for U1 and L5 ? \$\endgroup\$ – Damien Jan 2 at 11:38
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    \$\begingroup\$ @Damien. U1 - 750311564. L5 - 744311470. both wurth components. \$\endgroup\$ – JOHNDOE Jan 2 at 14:15
  • \$\begingroup\$ @JOHNDOE - Some more info would help. A short list off the top of my head: (a) Please add a photo of the h/w (so we can see overall layout, capacitor types etc.). (b) Please add images of PCB layout from the EDA s/w (Eagle?). (While some things might be visible on photo (a), these clear PCB track images may also help.) (c) What device is the 5V load with that "typical" current? (d) How do you know it isn't peaking above the range you gave? (e) I'm concerned about the caps (MLCC?) e.g. C4-C6 only rated at 6.3V on 7V rail! And C13 rated at 6.3V on 5V o/p - DC bias effect? What's your analysis? \$\endgroup\$ – SamGibson Jan 2 at 16:30
  • \$\begingroup\$ Think you have spotted the problem the caps rated voltages. Will adjust and check. The caps are ceramic x7r \$\endgroup\$ – JOHNDOE Jan 2 at 23:08
  • \$\begingroup\$ @samgibson Think you have spotted the problem the caps rated voltages. Will adjust and check. The caps are ceramic x7r \$\endgroup\$ – JOHNDOE Jan 10 at 5:48

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