Good, low-cost USB-C power supplies and cables are surprisingly hard to find, say the engineers at the Raspberry Pi Foundation, so they worked with Ktec to develop a suitable 5V/3A power supply for the Raspberry Pi 4 that provides an extra 500mA of current, ensuring a full 1.2A for downstream USB devices, even under heavy CPU load.. The supply is priced at $8, and is available in UK (type G), European (type C), North American (type A) and Australian (type I) plug formats.
The 4pin Power-over-Ethernet (PoE) connector remains in the same location, so the Raspberry Pi 4 remains compatible with the current PoE Hardware Attached on Top (HAT). This is a single-sided board that sits within the footprint of the Raspberry Pi and fits inside an official Raspberry Pi case. A small 25mm fan is pre-installed on the board to help with colling, and this is temperature-controlled over I2C via a small Atmel processor.
On the main board, MaxLinear's MxL7704 Universal PMIC is used to power the $35 Raspberry Pi 4, linking directly to Broadcom's BCM2711, a 1.5GHz quad-core 64-bit ARM Cortex-A72 CPU that provides three times the performance of the previous version.
It provides all key power rails required by the Raspberry Pi 4, including the low noise voltage rail used for audio circuitry. It also handles the unique power sequencing requirements of each rail with ease due to its convenient I2C programmability. The MxL7704’s I2C interface communicates with the computer’s SoC for dynamic voltage scaling, status monitoring, sequencing control and PGOOD routing. These features enable the Raspberry Pi 4 to save power by dynamically reducing the voltage to the SoC when the system is idle and boosting it when the processor is running at maximum speed.