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I've just had my first batch of PCB prototypes delivered from the manufacturer, and when I went to program them, the target voltage is reading too low. The device is based around an Atmel SAM L21 MCU, and I've attached a schematic for reference. The power supply is 3 AA batteries in series, connected to a Microchip MCP1711 3.3 LDO voltage regulator. In Atmel Studio, when I try to read the target voltage, it reads either 0.2v or 0.3v. I assume that because there is a voltage being read, that power is reaching the board, but I'm not sure why it's reading so low.

Does anyone have any suggestions as to what might be the problem? I've tested the batteries and the reading between them is reading around 4.5v, as it should be. Could this be a problem with the Atmel ICE programmer?

PCB schematic

Any suggestions would be great. Thanks guys!

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  • \$\begingroup\$ Have you checked to see if you have 3v3 present at the microcntroller and all the ICs?. I dont use the CAD program youve used, but I cant seem to spot the Vcc net anywhere on the regulators output. \$\endgroup\$ – Adil Malik Jan 24 '17 at 11:34
  • \$\begingroup\$ All VCC connections shown on the schematic are connected to a Power Plane on the board. edit Just realised the schematic shows a direct connection between VOUT on the voltage regulator and VDDIN on the microcontroller. VOUT actually goes to the power plane after the caps, and again from VDDIN on the microcontroller, to the power plane after the caps. (Hope that makes sense!) \$\endgroup\$ – Andy Mills Jan 24 '17 at 11:36
  • \$\begingroup\$ I am not familiar with this core but it might be worthwhile to double check that you have connected all of the VDDs that you need to and the voltage on Vout of your regulator. \$\endgroup\$ – RoyC Jan 24 '17 at 11:45
  • \$\begingroup\$ Maybe you can check the VDDCORE pin to see if the internal voltage is correct (VDD core is the output of the internal voltage regulator of the MCU). \$\endgroup\$ – Douwe66 Jan 24 '17 at 12:14
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    \$\begingroup\$ Not the battery nor the regulator is connected to a GND Symbol. This is not necessary if the layout editor knows that they have to be connected, but it smells like you forgot to connect battery minus to GND... \$\endgroup\$ – sweber Jan 24 '17 at 12:27
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It seems like you have used altium for you circuit. Usually the designators are used as numbers and the description of the pins is the description. As you currently did it, it is unclear wheter it is a net name or the designator of the pin.

Assuming from your comments, it is the pin designator, in which case you forgot to connect the ground of the battery to the rest of the circuit. As well as one of the ground pins of your microcontroller.

enter image description here

As a reference for you next circuit, this is the conventional way in altium to make your pin designators: It helps preventing confusion between net labels and pin designators.

enter image description here

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