I am going to use ST DALC112S1 (http://www.st.com/web/en/resource/technical/document/datasheet/CD00001317.pdf) to protect the SIM card connection between uBlox Leon G100 and the SIM card holder (VSIM, VRST, SIM_IO, SIM_CLK lines) against ESD.
This DALC112S1 has REF1 connected to the anodes and REF2 to the cathodes and it is clear that REF1 shall be a GND in this case (I have one GND for the whole circuit) but I don’t know if I should connect the REF2 to VSIM or better to a circuit Vcc (VSIM < Vcc(3.8V)).
Connecting it to VSIM is hazardous to Leon as there are no capacitors to absorb the voltage peak if it occurs. The circuit Vcc has lots of them but on the other hand there is a small risk that the whole circuit gets damaged with the ESD on the SIM. So, what is the usual way to do it?