Hi everyone,
I am working on a custom IoT board using the Quectel EC25-EUX mPCIe module. We are currently facing a SIM card detection issue and would appreciate some technical insight.
During the power-up sequence with a SIM card inserted, we observe the following behavior on the USIM_VDD line:
- It rises to 1.8V.
- It then switches to 3.0V.
- Finally, it drops to 0V and stays there.
The module fails to detect the SIM card. It appears the LTE module attempts to handshake with the SIM, but after failing to receive a valid response, it shuts down the interface to save power or prevent errors.
What we have checked:
- Physical connections of the SIM slot.
- The power-up sequence matches the Quectel Hardware Design guide.
- We suspect a communication timeout or a hardware mismatch in our schematic.
Requested Help: Could you please review our attached SIM interface schematic? Are there specific decoupling capacitor values or ESD protection placements (like GND plane issues) that could be causing this handshake failure?
Any advice on AT commands (e.g., AT+CPIN? or AT+QSIMDET) to debug the physical status would also be helpful.
Regards
