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I'm trying to debug a hardware issue where I am only seeing the feedback voltage on the output of a regulator that is part of a PMIC. The voltage divider that goes into the feedback pin have the correct resistor values. The inductor is properly placed onto the board and the switching frequency looks comparable to the datasheet. I'm thinking that the PMIC isn't properly placed on the board (it's a 48 pin QFN), but the switching pin and feedback pin on the part look like they're properly soldered. Should I use a heat gun and try to reflow the QFN part? Any other ideas? What about replacing the feedback resistors even though they're the appropriate values? I would hope that the issue would be something easy that is going over my head.

Any help is appreciated.

Part I'm referring to is the ADP5052ACPZ-R7, Regulator #4

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  • \$\begingroup\$ Can you check the continuity of the lower feedback divider to be sure it's connected? Maybe replace and re-solder it as well. \$\endgroup\$ – John D Apr 30 '18 at 17:07
  • \$\begingroup\$ How about the ground pin (PGND4)? \$\endgroup\$ – WhatRoughBeast Apr 30 '18 at 17:23
  • \$\begingroup\$ What device and what feedback resistor values? \$\endgroup\$ – Andy aka Apr 30 '18 at 17:34
  • \$\begingroup\$ Measure the voltages at each end of both feedback resistors using a fine probe on the top of the end caps. Measure the resistance from the feedback pin to ground and Vout with probes in both directions (power off, and output cap discharged, of course). See if anything looks anomalous. \$\endgroup\$ – Spehro Pefhany Apr 30 '18 at 17:48
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I would expect Pgnd4 pin has no contact to the board. If this is the not the case then compare shunt R voltage with FB4 input to read either 2.5 correctly or divided down from low output (fault). 2.5V is what you expect at FB when the output is correct.

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Issue was resolved. We reflowed the feedback resistors and now the device is regulating to the appropriate voltage level. Looks like the lower feedback resistor was not properly soldered during assembly (more specifically, PGND4). Thanks for any pointers.

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