Power and cooling challenges of the Raspberry Pi 5

Power and cooling challenges of the Raspberry Pi 5

Technology News |
By Nick Flaherty

The higher performance of the Raspberry Pi 5 has led to significant changes in the design of the board.

The Raspberry Pi 5 board consumes significantly less power and runs significantly cooler than Raspberry Pi 4 when running an identical workload, but the higher performance means peak power consumption increases to around 12W, versus 8W for Raspberry Pi 4.

The BCM2712 at the heart of the Raspberry Pi 5 is a 2.4GHz quad-core 64-bit Arm Cortex-A76 CPU with 512KB per-core L2 caches, and a 2MB shared L3 cache, giving twice the performance of the previous 1.8GHz chip.

The BCM2712 and the RP1 I/O controller designed in-house by Raspberry Pi are supported by the Renesas DA9091 “Gilmour” power-management IC (PMIC). This integrates eight separate switch-mode power supplies to generate the various voltages required by the board, including a quad-phase core supply, capable of providing 20 amps of current to power the Cortex-A76 cores and other digital logic in BCM2712.

The DA9091 is the product of a multi-year co-development effort starting with Dialog Semiconductor in Edinburgh. “We were able to squeeze in two frequently requested features: a real-time clock (RTC), which can be powered by an external supercapacitor or a rechargeable lithium-manganese cell; and a PC-style power button, supporting hard and soft power-off and power-on events,” said Eben Upton, CEO of Raspberry Pi.

The new design has seen a pair of mounting holes added to the board for a heatsink, as well as JST connectors for the RTC battery (two pins), Arm debug and UART (three pins), and fan with PWM control and tacho feedback (four pins).

An updated case for Raspberry Pi 5, priced at $10, adds usability and thermal-management features with an integrated 2.79 (max) CFM fan, with fluid dynamic bearings selected for low noise and an extended operating lifetime. This connects to the four-pin JST connector on Raspberry Pi 5 to provide temperature‑controlled cooling. Air is drawn in through a 360‑degree slot under the lid, blown over a heatsink attached to the BCM2712 AP, and exhausted through connector apertures and vents in the base.

A $5 Active Cooler attaches to the board via two new mounting holes, and connects to the same four-pin JST connector as the case fan.

When using a standard 5V, 3A (15W) USB-C power adapter with Raspberry Pi 5, the USB current is limited to 600mA to ensure sufficient margin to support these workloads. This is lower than the 1.2A limit on Raspberry Pi 4, though generally still sufficient to drive mice, keyboards, and other low‑power peripherals.

For users who wish to drive high-power peripherals like hard drives and SSDs while retaining margin for peak workloads, a $12 USB-C power adapter which supports a 5V, 5A (25W) operating mode. If the Raspberry Pi 5 firmware detects this supply, it increases the USB current limit to 1.6A, providing 5W of extra power for downstream USB devices and 5W of extra on-board power budget: a boon for those of you who want to experiment with overclocking your Raspberry Pi 5.

Users have the option to override the current limit, specifying the higher value even when using a 3A adapter. In testing, Raspberry Pi 5 functions perfectly well with typical configurations of higher-power USB devices, and all but the most pathological workloads.

Power over Ethernet

From early 2024, Raspberry Pi will be offering a Power over Ethernet (PoE+) add on board, or HAT. This supports the new location for the four-pin PoE header and has an L-shaped form factor which allows it to sit inside the Raspberry Pi 5 case without interfering mechanically or disrupting airflow.

The PoE+ HAT integrates a planar transformer into the PCB layout  and uses an optimised flyback converter architecture to sustain high efficiency across the whole zero to 25W range of output powers.

M.2 HATs

The Raspberry Pi 5 board also exposes a single-lane PCI Express 2.0 interface on a 16-pin, 0.5mm pitch FPC connector on the left-hand side of the board.

From early 2024, a pair of mechanical adapter boards will convert between this connector and a subset of the M.2 standard, allowing NVMe SSDs and other M.2-format accessories to be attached. The first, which conforms to the standard HAT form factor, is intended for mounting larger devices. The second, which shares the L-shaped form factor of the new PoE+ HAT, supports mounting 2230- and 2242-format devices inside the Raspberry Pi 5 case.

The company has also sourced a Panasonic lithium manganese rechargeable coin cell with a pre-fitted two-pin JST plug and an adhesive mounting pad. This is priced at $5 and is suitable for powering the Raspberry Pi 5 real-time clock (RTC) when the main power supply is disconnected.

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