2
\$\begingroup\$

I'm currently soldering, testing and validating the components on this PCB that I designed a few months back. PCB Printout As it is right now I have soldered the 1.2V, 2.5V, 3.3V and 5V buck converter power circuits and that schematic is shown below.Power Supply Schematic I have done continuity tests to check for shorts, that passed, and also haven't found any solder bridges. After continuity testing, I decided to power it just to do some initial testing of the output voltages for each converter to make sure the power planes were getting the correct voltages. This is the part I'm not fully understanding. When I check each output capacitor I get the same voltage as my Input Voltage (~15V).

I can't figure out if this means that every converter circuit is either designed poorly, soldered incorrectly, or an incorrect testing method. My current thought is that I'm completing the circuit from the power adapter, at my output capacitors, and reading the input voltage. That leads me to wonder if I need a load to test the output voltage correctly and how that could be implemented on a PCB that utilizes SMD components. If you have any suggestions I would appreciate it!

\$\endgroup\$
2
  • \$\begingroup\$ Ok that’s what I was thinking. I need to figure out how to go about attaching a load to the output. Thank you for the clarification! \$\endgroup\$ – JAlbers Mar 6 at 1:57
  • \$\begingroup\$ datasheet shows efficiency with a 100uA load minimum \$\endgroup\$ – Tony Stewart EE75 Mar 6 at 1:59
7
\$\begingroup\$

You appear to have pin 2 and 3 swapped on your TPS62120 symbol.

Pin 2 should be ground.

Pin 3 should be enable.

\$\endgroup\$
9
  • 1
    \$\begingroup\$ Yup, that'll be problematic. \$\endgroup\$ – ScienceGeyser Mar 6 at 5:55
  • 1
    \$\begingroup\$ I'm afraid you'll have to respin to correct this. While it's possible to rework a board it will be messy and fragile, not something you'd want to do on more than one board. And even though the TPS62101's likely survived this particular mis-wiring, the fact that all your rails output 15V very likely destroyed any chips they were connected to. \$\endgroup\$ – td127 Mar 7 at 15:12
  • 1
    \$\begingroup\$ Well, the absolute max is 17V so you should be fine. And your wall wart will likely be closer to 15V or a little lower under full load. \$\endgroup\$ – td127 Mar 8 at 2:33
  • 1
    \$\begingroup\$ 15V is the Recommended Operating Condition. But the Absolute Max is 17V so you're OK. If running that close to the edge makes you nervous, better to just change to a 12V wall wart rather than inserting components to drop down the 15V. \$\endgroup\$ – td127 Mar 9 at 3:32
  • 1
    \$\begingroup\$ The TPS62120 is pretty wimpy, limited to not much more than 50mA – is that enough? If so, you’re using very little power, less than a watt overall, so any wall wart from 9V to 15V will suffice. If your loads need more than 50mA you’ll need to find a beefier regulator. \$\endgroup\$ – td127 Mar 10 at 2:02

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.