Hey guys I'm trying to learn how to design PCB's. This is a design that I recently did for a servo module. What should I improve on?

Hi everyone!

I am building a CR Box, inspired by many designs on the r/crboxes subreddit.

This is my first ESP32-based design. I did the layout on 2 layers because I haven't used many components, and the highest intended signal frequency is the 25 kHz fan PWM (apart from the buck converter). I have tried my best to keep the bottom GND plane as intact as possible.

The fans are divided into two groups, A and B, to control the speed of the two fan groups separately. The ESP32 controls two MOSFETs using PWM, and each MOSFET is connected to the PWM pins of five fans. I added these 2 little MOSFETs to protect the ESP32 pins because, as far as I understand, the fans have an internal pull-up on their PWM pins, which can be as high as 5.25V. I added a "smart mode" switch, which, when OFF, lets me control the fans manually using the potentiometer. When the switch is ON, the controller will receive data from an air quality sensor and adjust the speed based on that. In addition, I connected each tachometer pin to the ESP32 to monitor the RPM of each fan and detect if one stops spinning.

For the power supply, the input voltage is 12 V. I added a P-channel MOSFET for reverse-polarity protection and a buck converter to step down the 12 V to 3.3 V to power the ESP32.

I designed the controller to support up to 10 fans. Each fan I am planning to use draws up to 0.35 A, giving 3.5 A in total. So I used a copper pour for the 12 V rail and wide traces towards the fan headers.

The PCB will be mechanically supported by the switch, potentiometer, and four M3 screws.

I’ve attached 3D renders of the board, the schematics, and the complete PCB layout.

I'd really appreciate any comments or advice on the design. I'm especially interested in feedback on how I control the fan speeds using PWM. Does the overall layout look okay? Are there any other issues or things you would change before I manufacture the PCB?

Thank you! 😊

System Architecture Overview

This schematic details an externally powered USB-C hub featuring DisplayPort Alternate Mode, dual USB-A downstream ports, and Gigabit Ethernet capability. The design is bound by a strict operational constraint: the hub must be powered externally and must not deliver power to the host device (phone) under any circumstances.

Functional Subsystems

1. USB-C Interface and DisplayPort Alt-Mode

• Protocol & Switching Control: USB-C Power Delivery (PD) and Alternate Mode negotiation are handled by the LDR6023SS controller. High-speed signal routing for DisplayPort Alt-Mode is multiplexed via the HD3SS460 switch.
• Power Isolation Topology: To enforce strict isolation, the host phone's VBUS line (usbc_VBUS) powers only the LDR6023SS. There is no electrical path connecting the hub's main power rails back to the phone's VBUS line, eliminating any possibility of back-powering the host.

1. Downstream Connectivity and Hub Expansion

• USB-A Ports: The TUSB8044ARGCR hub controller expands the upstream data connection into downstream interfaces, managing two physical USB-A 3.1 Gen 1 ports.
• Gigabit Ethernet: One of the downstream USB 3.1 channels from the TUSB8044A interfaces directly with a LAN7800 USB 3.1-to-Ethernet bridge to provide a dedicated 1Gbps network connection.

1. Power Generation

• External Power Supply: Except for the host-powered LDR6023SS, all internal subsystems (including the 3.3V, 2.5V, 1.2V, and 1.1V rails) are derived strictly from an external power block
• mux- HD3SS460- https://www.ti.com/lit/ds/symlink/hd3ss460.pdf?ts=1793132125218&ref_url=https%253A%252F%252Fwww.google.com%252F
• PD_negotiator- LDR6023ss- http://usbtech.net/upload/portal/20210129/713dd1a429631eed99f86d1b3961ad7d.pdf
• usb_hub- TUSB8044ARGCR- https://www.ti.com/lit/ds/symlink/tusb8044a.pdf?ts=1793125680672&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTUSB8044A
• ethernet- LAN7800/Y9X- https://ww1.microchip.com/downloads/aemDocuments/documents/UNG/ProductDocuments/DataSheets/LAN7800-Data-Sheet-DS00001992.pdf

I am trying to get my toes in the water of PCB design, and came up with this board to connect two TMC5240s to an STM32F7 to drive stepper motors. Board is simple for now, but will eventually have other versions with the drivers and stm on board.