Hello,
I’m working on a custom PCB integrating a Quectel EC25-EU (LGA) module with a Raspberry Pi Compute Module 5 (CM5) running Raspberry Pi OS Bookworm (64-bit). I’m using the USB interface to communicate with the EC25.
Problem:
The EC25 is correctly detected via USB after asserting the PWRKEY pin low for 500 ms, but after about 2 minutes it disconnects automatically. Below is the relevant dmesg log showing the disconnection event.
Hardware Setup:
- USB_BOOT: Initially left floating. It was at 1.8V, likely putting the module in forced download mode. I added a 10kΩ pull-down to GND, and the module started appearing in lsusb.
- USB_VBUS: Not connected in this design.
- USB_D+ / D-: Connected directly to CM5’s USB.
- PWRKEY: Controlled via GPIO3 using an N-MOSFET (FDN337N). Pulled LOW for 500 ms. After the pulse, PWRKEY stabilizes at 0.8V. The initial voltage in pwrkey is 0V before the turn on.
- STATUS, NET_MODE and VDD_EXT: Show 1.8V after power-up (seems OK).
Questions:
- Why might the EC25 disconnect from USB after 2 minutes?
- Could this be related to USB suspend, power-saving modes, or the missing USB_VBUS connection?
- Is there any AT command to keep the USB interface alive or disable automatic suspend?
- Could this be related to the schematic circuit to control the pwrkey pin?
Thanks in advance for your help!