Usim Operation - Sierra Wireless MC5725 Hardware Integration Manual

Note: For interface design
requirements, refer to:
(2G) 3GPP TS 51.010-1, section
27.17, or
(3G) ETSI TS 102 230 V5.5.0,
section 5.2
Rev 1.9.1 Feb.09
In the event of a discrepancy in values between this guide and the Product Specification Document (PSD), the PSD takes precedence.

USIM operation

When designing the remote USIM interface, you must make
sure that the USIM signal integrity is not compromised. Some
design recommendations include:
The total impedance of the VCC and GND connections to
•
the USIM, measured at the module connector, should be
less than 1 Ω to minimize voltage drop (includes any trace
impedance and lumped element components — inductors,
filters, etc.).
Note: The MC87xx is designed for use with either a 1.8 V or 3 V
USIM.
• Position the USIM connector no more than 10 cm from the
module. If a longer distance is required because of the
design of the host device, a shielded wire assembly is
recommended—connect one end as close as possible to the
USIM connector and the other end as close as possible to
the module connector. The shielded assembly may help
shield the USIM interface from system noise.
Reduce crosstalk on the XIM_data line to reduce the risk of
•
failures during GCF approval testing.
Avoid routing the XIM_CLK and XIM_DATA lines in
•
parallel over distances greater than 2 cm—cross‐coupling of
these lines can cause failures.
Keep USIM signals as short as possible, and keep very low
•
capacitance traces on the XIM_DATA and XIM_CLK signals
to minimize signal rise time—signal rise time must be <1 μs.
High capacitance increases signal rise time, potentially
causing your device to fail certification tests.
• Add external pull‐up resistors (15 kΩ — 30 kΩ), if required,
between the SIM_IO and SIM_VCC lines to optimize the
signal rise time.
• 3GPP has stringent requirements for I/O rise time (<1 μs),
signal level limits, and noise immunity—consider this
carefully when developing your PCB layout.
• The VCC line should be decoupled close to the USIM
socket.
• USIM is specified to run up to 5 MHz (USIM clock rate).
Take note of this speed in the placement and routing of the
USIM signals and connectors.
• You must decide if, and how much, additional ESD
protection and series resistors are suitable for your product.
The MC87xx already includes additional ESD protection.
Adding more protection (additional circuits) than is
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Host / Module Interfaces
67