Pico 2/RP235x: Differences between the A2 vs. A4 steppings

Raspberry Pi recently unveiled the A4 stepping of the RP235x microcontroller. This article explores some distinctions between the A2 and A4 versions, highlighting their impact on users and board designers.

What versions of the Pico 2 are available?

Raspberry Pi has recalled all RP2350 chips pre-A4 from authorized resellers. These chips will be utilized for Pico 2 board production until the supply is exhausted. Consequently, Pico 2 boards featuring the RP2350-A4 chip will not be available for several months.

What does this mean for designers using the Pico 2?

As a consequence, designers using Pico 2 should continue to design according to the A2 chip design recommendations. This includes using the workaround described in the document rp2350-datasheet, section "Appendix E: Errata, GPIO, RP2350-E9" in (https://pip.raspberrypi.com/categories/1214-rp2350)

Will this cause any issues long-term?

There is no downside to implementing the workaround for errata "E9" (For GPIO pads 0 through 47, Driving / pulling the pad input low with a low impedance source of 8.2 kΩ or less) on the future Pico 2 A4; one can design for A2 and switch later to A4 without impact on the design.

What about the GPIO voltage tolerances? Are they different between the A2 and the A4?

There is no functional difference in the RP235x 5V GPIO tolerance between the A2 stepping and the A4 stepping. The same GPIO circuitry was used for both, but only A4 was officially validated. This validation, although done only on A4, should also apply to A2 and A3 stepping (as it is the same circuitry).

As a consequence, Raspberry Pi is now convinced the chip's GPIO will tolerate +5V for the A2 to A4 steppings, as long as the RP235x is powered up before +5V is applied to the GPIO pins.