Powering the Raspberry Pi; a Case Study

Since its launch in 2012, the Raspberry Pi has become a bit of a phenomenon. Initially conceived to introduce schoolchildren to programming, the pocket-sized, Linux-based computer quickly became the best selling computer ever to be designed in the UK with over 20 million unit sales to date. From the classroom, the computer has moved into the home for control applications and even into industrial area in commercial usage. There have been many designs using the Raspberry Pi by both hackers and professionals, and the board has one of the most vibrant communities in the electronics industry.

There have been several variations of the board, and the latest version, the Raspberry Pi 3B+ is the most powerful and complex of them all. Of course, as we all know, a complex board needs a complex power supply, and the Raspberry Pi 3B+ is no different in that respect. The board required six voltage rails – two 3.3V rails with one being “quiet” for audio, 1.8V, two 1.2V rails with one for the CPU and one for memory and the last rail being a 5V master supply that would be used to drop the voltage down to those needed by other rails, as well as being used to supply the downstream USB ports. The CPU supply voltage also had to have the ability to be raised or lowered depending on the CPU workload and the input voltage would be supplied through a single micro USB connector.

It wasn’t just the electrical specifications that were demanding, the power solution for the Raspberry Pi 3B+ would have to be small enough to fit in the traditional credit card sized form- factor of the board with the other components and without disturbing their operation. Possibly the toughest task of all would be to keep the solution within the pre-set cost budget that would be suitable for an educational board.

The designers of the Raspberry Pi turned to Exar, who have since been bought by MaxLinear, for a solution. MaxLinear managed to accomplish the task and provided the solution in a single small QFN chip in under a year. It was a major achievement as the previous iteration of the Raspberry Pi had problems with power and tended to overheat. They’ve told the full story of the task and how they solved it in a new blog you can read here - https://www.raspberrypi.org/blog/pi-power-supply-chip/.

PSD