Raspberry Pi 4 Model: B !free! Full Schematic
Understanding the Raspberry Pi 4 Model B "Reduced" Schematic If you’ve ever looked for a "Full Schematic" of the Raspberry Pi 4 Model B
, you’ve likely hit a wall. Unlike early models, the Raspberry Pi Foundation now only releases Reduced Schematics. These official diagrams provide just enough detail for hardware designers and hobbyists to build add-ons without exposing proprietary design secrets. What’s Included in the Official Schematics?
The official documentation serves as a high-level technical reference for engineers. Key sections typically covered in these diagrams include:
Broadcom BCM2711 SoC: The brain of the board, a 64-bit quad-core processor @ 1.8GHz.
40-pin GPIO Header: Detailed pinout for interfacing with sensors and HATs.
USB-C Power Input: Wiring for the 5V DC power supply (minimum 3A recommended).
Dual Micro HDMI Ports: Pin configurations for the two 4Kp60 supported displays.
PoE Header: Dedicated pins for using a Power over Ethernet HAT.
AV Jack: The 4-pole stereo audio and composite video port layout. Why You Won't Find a "Full" Version
The Raspberry Pi Foundation has explicitly stated in community forums that full schematics—including all component values, traces, and internal layers—are unlikely to be released. This is largely due to the proprietary nature of certain parts of the board design and the Broadcom SoC. Where to Find More Technical Details
For those looking to dive deeper than the basic schematics, you can reference these authoritative technical documents:
Official Reduced Schematic (PDF): The most accurate starting point for hardware developers. Raspberry Pi 4 Model B Full Schematic
Raspberry Pi 4 Model B Datasheet: Includes electrical specifications, power requirements, and GPIO multiplexing modes.
Raspberry Pi 4 Product Brief: Provides physical specifications and mechanical dimensions in millimeters.
Pro Tip: If you are designing a custom PCB or carrier board, look into the Compute Module 4 (CM4) documentation. It is "loosely based" on the Pi 4 Model B
and often provides more granular interface data for industrial designers.
Are you planning to build a custom expansion board or just trying to troubleshoot a specific component on your Pi? Raspberry Pi 4 Model B specifications
Understanding the Raspberry Pi 4 Model B requires a deep dive into its hardware architecture. While a complete, 100% unrestricted schematic is rarely released for proprietary reasons, the official Reduced Schematics provided by Raspberry Pi Ltd. offer a comprehensive view of the board's core systems. Core Architecture and the BCM2711 SoC
At the heart of the Raspberry Pi 4 is the Broadcom BCM2711 System on Chip (SoC). Unlike previous generations, the Pi 4 separates many of its high-speed I/O functions from the main processor into specialized controllers.
Processor: Quad-core Cortex-A72 (ARM v8) 64-bit SoC running at 1.5GHz or 1.8GHz depending on the revision.
Memory Integration: The schematic reveals a dedicated high-speed bus connecting the SoC to LPDDR4-3200 SDRAM, which is available in 1GB, 2GB, 4GB, or 8GB configurations. Power Management and USB-C
One of the most critical sections of the schematic is the Power Management Integrated Circuit (PMIC). The Pi 4 uses the MaxLinear MXL7704.
USB-C Power Input: It requires a 5V / 3A DC input via USB-C. Understanding the Raspberry Pi 4 Model B Go
Voltage Regulation: The MXL7704 manages multiple power rails, including synchronous buck converters for the core SoC voltage and linear regulators for sensitive analog components.
Protection: The schematic shows circuitry for power-on-reset and over-voltage protection, ensuring the board handles power surges gracefully. High-Speed Connectivity and I/O
The Pi 4's schematic layout illustrates a significant shift in I/O handling compared to its predecessors.
USB 3.0 and PCI Express: For the first time, USB 3.0 is provided via a VIA VL805 PCIe to USB 3.0 controller. This bypasses the older shared USB/Ethernet bus, allowing for much higher throughput.
Dual Display Support: The schematic details two Micro-HDMI ports, each capable of driving 4K displays at 60fps.
Ethernet: True Gigabit Ethernet is implemented via the Broadcom BCM54213PE PHY, which connects directly to the SoC’s RGMII interface. The 40-Pin GPIO Header
The standard 40-pin GPIO header remains backwards compatible but adds new multiplexed functions.
New Interfaces: The Pi 4 schematic reveals additional UART, I2C, and SPI channels that can be mapped to various pins, giving developers more flexibility for complex hardware projects.
PoE Support: A dedicated 4-pin header is visible near the Ethernet port, specifically designed for use with the official PoE HAT. Where to Find the Files
For a complete visual inspection of the circuit paths, you can download the following official and community-sourced documents:
Official Reduced Schematics (PDF): The primary source for electrical diagrams. USB-C Input (J7): Do not confuse this with
Official Model B Datasheet: Provides the electrical specifications and pinout details.
Community Resources: Platforms like Geekworm Wiki and ResearchGate often host mirrored versions of these diagrams for easy access. Raspberry Pi 4 Model B specifications
Page 2-3: Power Distribution (The PMIC Core)
This is the most complex section. The Pi 4 requires multiple voltage rails: 3.3V, 1.8V, 1.1V (Core), 0.8V (DDR4), and 5V (USB/VGA).
Key Components on these pages:
- USB-C Input (J7): Do not confuse this with a standard USB-C schematic. The Pi 4 uses a novel configuration to negotiate 5.1V at 3A without full USB-PD logic.
- MxL7704: This chip manages sequencing. If your Pi 4 doesn't turn on, you diagnose here. Look for the
PWR_EN,3V3_EN, andRUN_PG(Power Good) signals. - PPTC Fuses: Note the F1 and F2 polyswitches on the 5V input. These are sacrificial resetting fuses.
2) SoC, DDR and memory interface
- SoC pinout: DDR, CPU core, and high-speed interfaces are routed with matched-impedance, differential pairs and tight length-matching as shown on the schematic and layout constraints.
- DDR4/LPDDR4 interface: The schematic exposes the memory devices, VDD/VDQ rails, and termination networks. Note the specific decoupling strategy and power-switching for VDDQ and VDDCore.
- Clocking: Dedicated oscillators and spread-spectrum clocking for PCIe/USB/GPU/CPU domains. Crystal selection and load capacitances are shown.
Practical notes:
- Adding or changing DDR components is nontrivial; preserve trace lengths and termination from the reference design.
- Use the provided testpoints for probing DQS/DQ timing only with differential scope probes and minimal loading.
3.5. Boot and Configuration
- EEPROM (SPI flash) – Winbond W25X40CL: Contains the bootloader and board configuration.
- Boot mode selection resistors: Determine whether to boot from SD card, EEPROM, or USB.
- Run (reset) button header – a rarely documented but useful hardware reset point.
3.2. Power Management IC (PMIC) – MxL7704
A dedicated section covers the MaxLinear MxL7704 PMIC. The schematic reveals:
- Four buck converters producing 1.8V, 3.3V, 1.2V (for LPDDR4), and 0.9V (core).
- Power-on reset (POR) timing and enable sequencing.
- Thermal monitoring connections and fault indicator outputs.
What is publicly available (official sources)
-
Reduced schematic (PDF) – Shows major power rails, HDMI, USB, Ethernet, GPIO, etc.
- Available from the official Raspberry Pi hardware documentation:
https://datasheets.raspberrypi.com/rpi4/raspberry-pi-4-schematics.pdf - This is not a full netlist-level schematic (e.g., no internal BCM2711 connections, no exact passives values in all cases).
- Available from the official Raspberry Pi hardware documentation:
-
Mechanical drawing – Board dimensions, mounting holes, connector locations.
-
BCM2711 ARM Peripherals datasheet – GPIO, I2C, SPI, PWM, etc. register-level info.
5. Connectivity Architecture
The Pi 4 Model B schematic showcases the distinct separation of high-speed data lanes via a PCIe-to-USB bridge.