0
\$\begingroup\$

I purchased a couple of AP63356QZV-7 switching regulators for testing and I have not been able to get a stable 5 V. Instead, I have observed square waves that can peak to approximately 3.5 to 5 V.

The test board I have assembled has the component values recommended in the datasheet to get 5 V at the output. Screenshot of the schematic. The highlighted section shows the parts used in this test.

The Vin is 12 V and the load current ~2.3 A. I changed the load current to ~2 mA and have not seen much of a difference.

I have tried resoldering the components and have had no change in the output.

Here is a picture of the voltage at the load:

Image of Vout with the Oscilliscope

Any ideas on what can be causing this issue?

EDIT Here is a schematic of the exact circuit setup. I added a few bridges to have different options such as using external compensation. The 6.8 μH inductor I used in the circuit is the NRS8040T6R8NJGJ.

enter image description here

\$\endgroup\$
6
  • 2
    \$\begingroup\$ Could you add a picture of the circuit setup? \$\endgroup\$
    – Big6
    Jul 7, 2022 at 1:08
  • \$\begingroup\$ Did you put the two 22 µF capacitors for C2 in series or in parallel? \$\endgroup\$
    – ocrdu
    Jul 7, 2022 at 7:56
  • \$\begingroup\$ Can you add a link to the datasheet for your inductor? \$\endgroup\$
    – John D
    Jul 7, 2022 at 14:30
  • \$\begingroup\$ In my application I use the soft start feature of this chip with a capacitor of 100 nF between EN pin and GND. It is worth a test. \$\endgroup\$
    – Jens
    Jul 7, 2022 at 15:28
  • \$\begingroup\$ Have you measured other signals like the sw-node to check if the chip is remotely working as expected? \$\endgroup\$ Jul 7, 2022 at 18:31

1 Answer 1

0
\$\begingroup\$

This converter senses current through the built-in high side MOSFET, and shuts down if the current exceeds 5 amperes for 512 cycles. It stays off for 8192 cycles, then restarts. This is what you are seeing as your device attempts to start repeatedly. Even when lightly loaded, current must be supplied to the output capacitors to charge them up. As a test, you might try removing or reducing the output capacitors while running with a light load to limit the pulse current.

The culprit may be the current rating of the inductor. It is likely saturating and hitting the current limit at every set of start-up pulses. For a 2.3-A supply, I suggest an inductor with a 5VDC rating.

Good luck!

\$\endgroup\$
2
  • \$\begingroup\$ I use the same circuit with a much worse inductor with 120 mohm and Isat 1.8A without a problem, but using a soft start capacitor. The output voltage is up before the end of the soft start. The bad coil was chosen because I need only 500 mA load current. \$\endgroup\$
    – Jens
    Jul 8, 2022 at 14:07
  • \$\begingroup\$ Thanks for all the help from everyone! Turns out that it was a manufacturing error. The switch and the Vout planes were shorted together. \$\endgroup\$ Jul 8, 2022 at 21:48

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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