Recently, I designed a custom carrier board for Raspberry Pi CM4. Most design requests that I received these days were for Raspberry Pi CM5. Hence this was probably the only CM4 design request that I’ve received in this year 2025.
After my design is completed, my client ordered PCBA prototyping from JLCPCB, and started testing. As I expected, the prototype testing unveiled a few design issues related to power supply and some IO ports. Those issues were specifically related to the custom IO features used in this board. But he found a very interesting problem while testing with Raspberry Pi CM4 Lite. The CM4 Lite was not booting from SD card, which has Raspberry OS pre-flashed and tested on the official Raspberry Pi IO board.
By comparing the board’s schematics with the schematics of the official Raspberry Pi CM4 IO board, he found the difference between my design and the official design. He added a 10kΩ pull-up resistor by hand soldering and it solved the board with Raspberry Pi CM4 Lite booting from SD card.
After knowing this from my client, I surveyed what made this problem. First of all, I used my recent CM5 carrier board design resources for designing this CM4 carrier boards. But as I made my base design resource compatible with both CM4 and CM5, I didn’t care about it much while designing. I’ve tested my boards before using both CM4 and CM5 and they were all working good. But it was because I only tested with eMMC version of CM4 and CM5, and never tried with Lite compute modules.
By comparing the schematics of official IO boards for Raspberry Pi CM4 and CM5, I found that CM4 IO board had a 10kΩ pull-up resistor on SD_PWR_ON pin and CM4 IO board had not.
Next, I tried to search similar issues on Raspberry Pi Forum, but I could not find similar problem reported.
I then read the CM4 datasheet adn CM5 datasheet for SD card part, and found the difference in it. It was a little surprising to me, because I was expecting some difference between CM4 and CM5’s SD card power pull-up configuration. But both datasheet were explaining the need of pull-up resistor on SD_PWR_ON pin.
So, as per datasheet, not only CM4 Lite, but also CM5 Lite won’t be booting from SD card on my custom carrier boards and the official CM4/CM5 IO boards. I and my client didn’t have a CM5 Lite modeul te test at this time of writing. Hence, we could not evaluate.
Why does not the official CM5 IO board have pull-up resistor on SD_PWR_ON pin? I could not know. Maybe Raspberry Pi CM5 have no plan to release the Lite model? I stopped further researching here and left as an open question.
Thank you for reading.
