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My input voltage is 7.4 and I need to step it down to 6.5 with a 3A current. I've used an xls file from the supplier to calculate the followin scheme: enter image description here

I might made some mistake in my PCB here:

enter image description here

But it doesn't work. It gives just 0,8V on Vout.

Here are the calculation results: enter image description here enter image description here

EDITED: I've read the circuit notes in the datasheet and done some changes. Do you think this circuit can work? enter image description here

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    \$\begingroup\$ I'm not sure whether this would be enough to cause the regulator to fail, but that is a pretty bad layout for an SMPS. Take a look into app notes and eval kits, but in essence: keep switching loops small, power traces fat and short, key components (capacitors, inductors, diodes) should be carefully placed. \$\endgroup\$ – Wesley Lee Apr 28 '18 at 8:58
  • \$\begingroup\$ It is already tiny enough. I can’t imaging it is possible to make it shorter with chip pins placed this way. \$\endgroup\$ – Anton Zimin Apr 28 '18 at 9:03
  • \$\begingroup\$ The traces are long and thin. Tiny PCB != short traces. \$\endgroup\$ – Wesley Lee Apr 28 '18 at 9:17
  • \$\begingroup\$ Not sure it could give such a drop of voltage. \$\endgroup\$ – Anton Zimin Apr 28 '18 at 10:15
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    \$\begingroup\$ It really could. You only need a fraction of a volt error on a feedback pin to completely mess up the regulation and protection circuitry. This explanation may help. electronics.stackexchange.com/questions/67894/… A good way to re-lay out the board would be to use a 2-layer PCB with the entire second layer as a ground plane. \$\endgroup\$ – Brian Drummond Apr 28 '18 at 10:32
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I’ve made a new design for the board with fat traces and short loops and it works perfectly.

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  • \$\begingroup\$ Cool! Is it the circuit that you posted on your edit? \$\endgroup\$ – Wesley Lee Apr 30 '18 at 12:31

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