The TXS4558 is a complete dual-supply standby Smart Identity Module (SIM) card solution for interfacing wire-less baseband processors with two individual SIM subscriber cards to store data for mobile handset applications. It is a custom device which is used to extend a single SIM/UICC interface to be able to support two SIM’s/UICC’s.

The device complies with ISO/IEC Smart-Card Interface requirements as well as GSM and 3G mobile standards. It includes a high-speed level translator capable of supporting Class-B (2.95 V) and Class-C (1.8 V) interfaces, two low-dropout (LDO) voltage regulators that have output voltages that are selectable between 2.95-V Class-B and 1.8-V Class-C interfaces. Simple GPIO inputs are used to switch between the two SIM cards and to put it into different modes. The voltage-level translator has two supply voltage pins. VCC sets the reference for the baseband interface and can be operated from 1.65 V to 3.3 V. VSIM1 and VSIM2 are programmed to either 1.8 V or 2.95 V, each supplied by an independent internal LDO regulator. The integrated LDO accepts input battery voltages from 2.3 V to 5.5 V and outputs up to 50 mA to the B-side circuitry and external Class-B or Class-C SIM card.

The TXS4558 also incorporates shutdown sequence for the SIM card pins based on the ISO 7816-3 specification for SIM cards. The device also has 8kV HBM protection for the SIM card pins and standard 2kV HBM protection for all the other pins.