on resistance of bus switch not acceptable, at least not for Vcc
As can be seen from the IDTQS3244 data sheet, the ON resistance is higher tham 16 ohms in case of a 3.3V power input (VCC_PHONE).
This causes significant voltage drop over the switch, resulting in way too low supply voltage arriving at the SIM card.
It seems like we really need to re-think the switching concept. A short-time fix might be to supply power from the SIMTRACE to the sim, rather than passing it through. However, even for the CLK/IO/RST signals the 16Ohms might cause significant signal degradation.
#1 Updated by tsaitgaist over 7 years ago
- Resolution set to fixed
the bus switch has been changed : a type CB3Q (CB3Q3244) it now used instead of the QS3244.
It has a Ron of ~5 Ohms and always <=9 Ohms.
change made in git 13b6eff33a7c0d41c47080f26fdedd18db1c1c45
The VCC_PONE/SIM is now on a separate circuit. VCC_SIM can either be powered by VCC_PHONE (sniff,mitm) using the power switch (FPF2005), or can be powered (card reader mode) by the second output of the new LDO (AP7332 replaces TPS73633)
change made in git bcd3695c1a47c07dc073762b33afec24caf2a939