Easyduino STM32F103

ESP32

The most popular WiFi Microcontroller

Schematic

KiCad Schematic symbols, footprints and 3D Models were obtained from their KiCad Github repository

Gerbers

Specs

• Input Voltage: 5V-15V(External Source 5V Pin) 5V (USB) or 3.3V (3.3V Pin). ONLY USE ONE VOLTAGE INPUT AT A TIME
• Output Current at 3.3V : 1 A (External Source) 500mA (USB)
• No Polarity Protection (External Source)
• Overcurrent Protection: None

References

ESP32 WROOM 32E

Decoupling capacitors

• ESP32 Wroom 32 E datasheet p24 -> 3.3V pin needs one 22uF and one 100nF capacitors

Enable pin (EN)

• ESP32 Devkit sch -> EN pin 10k resistor and 100nF capacitor

Thermal Pad

• ESP32 Wroom 32 E datasheet p26 -> GND Thermal needs vias between pads. Needed vias are too small for my manufacturer. I will use bigger vias

Automatic Bootloader

• ESP32 Devkit sch -> Automatic Bootloader.

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 -> VBUS will be tied to REGIN. 1uF and 100 nF will be added.
• CP2102 datasheet p15 -> ESD Supression Diode for all three inputs of USB
• CP2102 datasheet p15 and p19 -> 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. I will not use this as a voltage provider for the ciruit. I will use the AMS1117-3.3
• CP2102 datasheet p15 -> RST pulled up via 4.7k and SUSPEND~ pulled down via 10k.

AMS1117-3.3V

• AMS1117 Datasheet p1 -> 3.3V/1A Output with 5-15V Input
• AMS1117 Datasheet p4 -> 22uF tantalum capacitor on input and output.

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