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Atmega32u4 has 7 VCC pins. Can I connect 1 of the 7 VCC pins to the power supply to power the MCU, and use the rest of the VCC pins (6 of them) on the MCU to power other peripherals, such as LEDs?

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    \$\begingroup\$ These are for power input, not output. Please use these as intended, even if it might seem to work. \$\endgroup\$
    – Eugene Sh.
    Sep 19, 2017 at 19:43
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    \$\begingroup\$ Even if they are connected internally, you could be overloading the internal bonding wires and/or be providing poorer supply than expected by the IC (than if powering every pin with proper bypassing). \$\endgroup\$
    – Wesley Lee
    Sep 19, 2017 at 19:44

2 Answers 2

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Not sure where you see 7. The datasheet shows 2 AVCC, 2 VCC, 1 UVCC and 1 VUSB.

The 2 AVCC are used to power the Analog circuitry, and not connecting them, and not filtering it, would mean shitty analog to digital or digital to analog conversions. If you don't need the ADC or DAC features it's not mandatory.

The VCC powers the digital circuitry. You should connect both. YMMV if you don't. Drawing too much power cab cause issues then.

The UVCC is for powering the USB circuitry. Again if you don't use it...

VBUS is actually an input that connects to USB power, for sensing when a usb cable is connected.

And there is the GND pins. All should be connected. Technically one tends to be AGND but still, connect it.

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  • \$\begingroup\$ +1 for right answer, with a small correction: the input pin is named VBUS, not VUSB. \$\endgroup\$ Sep 19, 2017 at 20:49
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    \$\begingroup\$ I'm not sure if I misunderstood the answer "If you don't need the ADC or DAC features it's not mandatory". However, while filtering is not mandatory if you don't use ADC and comparator, connecting AVCC to VCC is mandatory, to power up the port shared with analog functions (Section 2.2.17: AVCC is the supply voltage pin (input) for all the A/D Converter channels. If the ADC is not used, it should be externally connected to VCC. If the ADC is used, it should be connected to VCC through a low-pass filter.). \$\endgroup\$
    – next-hack
    Sep 20, 2017 at 6:14
  • \$\begingroup\$ @next-hack should is not must. There's another question on here specifically about AVCC in avrs that answers this. \$\endgroup\$
    – Passerby
    Sep 20, 2017 at 12:37
  • \$\begingroup\$ @Passerby On other parts of the datasheet (24.1), they make it clear: "The ADC has a separate analog supply voltage pin, AVCC. AVCC must not differ more than ± 0.3V from VCC.". This is repeated also on the limiting values in the table 29.7. And also in all the schematics (also during programming: note 2 of figure 28.10) So that "should" is actually a "must" (ok, you don't have to connect it to the same VCC source, but to another source with -at the end of the day- the same voltage value of VCC). \$\endgroup\$
    – next-hack
    Sep 20, 2017 at 12:49
  • \$\begingroup\$ Instead, as you said, UVCC can be left open in some cases (Fig. 21.6). \$\endgroup\$
    – next-hack
    Sep 20, 2017 at 12:53
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Yes you need to supply power to each Vcc pin and NO you can't feed power through the chip to other devices, LEDs etc.

The multiple VCC pins provide proper power distribution around the wafer. If you only use one a) it may not work, and b) that one pin may not be able to carry the max current and the bonding wire may burn out.

If you attempt to use the other Vcc pins as power routing, you are routing ALL the power through the chip. That just makes things worse. Further, any switching of those devices would cause current spikes in the Micro.

Addition: You ALSO need to add decoupling capacitors close to each of those Vcc pins.

Addition 2: You did not ask, but the same goes for all the ground pins.

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    \$\begingroup\$ OPs wording is poor. "No." applies for the question on the body, but not on the title. May be confusing for some readers. \$\endgroup\$
    – Wesley Lee
    Sep 19, 2017 at 19:46
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    \$\begingroup\$ With a little correction: if VBUS is on the OP's list, it shouldn't be "provided" from local power supply; it should be connected to USB connector, to sense the cable connect event.. \$\endgroup\$ Sep 19, 2017 at 21:01

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