UICC

nRF9151 Hardware Design Guidelines

The Universal Integrated Circuit Card (UICC) interface is used to communicate with a Universal Subscriber Identity Module (USIM) or Embedded SIM (eSIM). The UICC interface is commonly known as the Subscriber Identity Module (SIM) card interface. It consists of SIM_RST (pin 16), SIM_DET (pin 26), SIM_CLK (pin 18), SIM_IO (pin 17), and SIM_1V8 (pin 19).

nRF9151 supports UICC Class C interface with 1.8 V nominal voltage as described in ETSI TS102 221. If needed, support for higher supply voltage classes must be built with external components, including an external power supply and level shifters towards the UICC interface of the Long-Term Evolution (LTE) modem.

The LTE modem controls the following physical interfaces towards the UICC and implements the transport protocol over the ISO/IEC 7816-3 interface:

  • SIM_1V8 (power supply): LTE modem driven
  • SIM_CLK (clock signal): LTE modem driven
  • SIM_RST (reset signal): LTE modem driven
  • SIM_I/O (input/output serial data): Bi-directional
  • SIM_DET (reserved for card detection, not in use)

Features

If the device has a user-accessible slot for a UICC, consider its Electrostatic Discharge (ESD) sensitivity. The nRF9151-internal ESD protection is intended for a 1.5 kV Human Body Model (HBM) level. External ESD/EMI filtering is recommended between the UICC card slot and nRF9151.

Several ESD/EMI filtering options are available. A commonly used option is a dedicated integrated component, such as STM EMIF03-SIM02M8 or TI TPD3F303. Typically, an integrated ESD filter consists of low pass filters and ESD diodes in a small SMD package. Another option is discrete ESD protection which takes more space on the PCB but can be more flexible for certain applications and a lower-cost solution.

Discrete ESD protection can consist of the following components:

  • Bypass capacitors in the range of ≤ 22 pF to SIM_RST, SIM_CLK, SIM_IO, and SIM_1V8.
    • A separate supply capacitor ranging from 100 nF to 220 nF connected to SIM_1V8 can be considered.
  • Low capacitance type ESD diodes to SIM_RST, SIM_CLK, SIM_IO, and SIM_1V8.
    • Multichannel ESD diodes are commonly used and recommended.
    • Some multichannel diode components incorporate EMI filtering. This type is recommended if the product integrates an LTE antenna, or if an external antenna is located close to the SIM holder.

The electrical specifications for all UICC signals that should be verified in product design and in the prototyping phase are defined in ETSI TS 102 221, chapter Electrical specifications of the UICC. For more information, see nRF9151 Hardware Verification Guidelines.

PCB layout design

When designing the PCB layout, consider the following recommendations for the UICC interface:

  • If the product integrates a Global Navigation Satellite System (GNSS), LTE, or DECT NR+ antenna, avoid placing the SIM card holder close to the antenna due to the risk of digital noise coupling from the SIM application to the antenna.
  • Place the UICC application as close to nRF9151 as possible to minimize the routing length. Long routing reduces signal integrity in the UICC interface and increases the risk of radiated noise.
  • Use the same application board ground plane for the UICC application and nRF9151's GND to guarantee low impedance ground connection between nRF9151 and the UICC application.
  • Avoid routing the UICC interface close or adjacent to sensitive RF routings, such as GNSS or ANT.
  • Place the ESD and EMI components or discrete components as close as possible to the UICC application's pins SIM_RST, SIM_CLK, SIM_IO, and SIM_1V8 to optimize their performance.
  • For debugging purposes, consider test points in SIM_RST, SIM_CLK, and SIM_IO.