Easyduino/Atmega328p Arduino Nano

Easyduino Arduino Nano

The popular Nano version of the Arduino

Schematic

Gerbers

Specs

• Input Voltage: 5.5V-9V(External Source Vin) 5V (USB). Both can be used at the same time. Preferable to only power from one source
• Output Current: 250 mA (External Source) 500mA (USB)
• 3.3V Output Current: None (External Source) 100 mA (USB)
• No Polarity Protection (External Source)
• Overcurrent Protection: None (External Source) 1A (USB)
• 5V Autoselector: can take both USB and external source. A diode will avoid short circuit.
• External input Polarity Protection: None!!

References

Atmega 328p

Reset

• Atmega Hardware Design Considerations p7,p8 -> 10kR and 330R for switch. The 100nF capacitor is not used for Arduino (Produces errors with DTR)
• The 100nF capacitor on DTR (CP2102) is used for tricking the Atmega into Bootloader mode

Crystal

• Atmega Hardware Design Considerations p16 -> 22pf

AVCC

• Atmega328 Reference Manual p213 -> 10uH ferrite bead and 100nF.
• The Analog tracks aren't critical. I won't create an analog ground for these tracks.
• I also won't add the 10 uH ferrite

AREF

• Atmega Hardware Design Considerations p6 -> 100nF

USB-C

Filtering

• USB Hardware Design Guidelines for FTDI ICs p8 -> 10nF Cap + Ferrite Bead + 100nF Cap + 4.7uF Cap
• I disregarded such heavy filtering for the easier to implement 1uF and 100nF cap given in the CP2102 datasheet
• I added a polyfuse with Ihold=500mA and Itrip=1A.

Differential Pair

• USB needs 90 Ohm differential traces.

• According to JLCPCB impedance calculator, with a JLC7628 prepreg and 6mil (0.15mm) space between lines

• I have to use 9 mil tracks -> 0.2 mm

• I will use a very short trace for D+ D- (around 2mm)

• I have to place vias because of the pinout of USB C and CP2102. Some other people have done it with no problems

CP2102

• CP2102 datasheet p15 -> 1uF and 100nF for REGIN and VBUS
• CP2102 datasheet p15 -> 100nF for VDD output, 4.7 uF is optional for higher current circuits.
• CP2102 datasheet p23 -> The VDD or 3.3 output can only provide 100mA
• CP2102 datasheet p23 -> Logic levels go up to 3.3 V, but Atmega328p is able to understand them. Despite being 5V
• CP2102 datasheet p15 -> RST and SUSPEND resistors have not been placed. Might produce bad results due to noise

XC6206P

• XC6206 Torex Datasheet p1 -> 1uF ceramic capacitor on input and output. 7V Maximum operating Voltage
• XC6206 UWM Datasheet p2 -> 1uF ceramic capacitor on the input and output. 9V Maximum operating Voltage

5V autoselector

• If USB is present and no external input voltage. The USB will power the ATMEGA
• If USB is present and there is external input voltage. The external voltage will power the ATMEGA
• If USB is not present and there is external input voltage. The external voltage will power the ATMEGA. The 3.3V output won't work

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