Sierra Wireless AirPrime WP8548, Hardware Integration Manual, Page: 15 / 26

Routing Constraints and Recommendations
Rev 2 Feb.16 15 Specifications subject to change
Note: Figure 4-1 shows separate traces for VBAT_BB and VBAT_RF. If VBAT_BB and
VBAT_RF share a single power supply, these traces should be connected.
Note: For optimal decoupling, place the capacitors on the underside of the board, directly
under the pins.
• Filtering capacitors (100 nF to 1500

F) are recommended near the module’s
power supply.
• Attention should be paid to the ground trace or the ground plane on the appli-
cation board for the power supply that supplies the module. The ground trace
or ground plane, as well as the VBAT trace, must be able to support current
peaks.
• If the ground trace between the module and the power supply is a copper
plane, make sure it is a solid plane.
• Design routing to make sure total line impedance does not exceed
10 m

@ 217 Hz.
Ground Plane Connection
The AirPrime WP8548 module requires a solid, central ground plane (with solder
mask defined pads) located directly under the module. This will:
• Ensure high current signal returns
• Provide heat dissipation under higher operating temperatures
The ground plane should be connected (with vias) to the reference ground layer
of the application board.
UIM Interface
• The length of the tracks between the AirPrime WP8548 and the UIM socket
should be as short as possible. Maximum recommended length is 10cm.
• ESD protection is mandatory on the UIM lines unless:
· An ESIM is being used, or
· There is no physical access to the UIM
• The decoupling capacitor(s) should be placed as close as possible to the UIM
card connector for the UIM1_VCC signal.
RF Circuit
The RF signal must be routed on the application board using tracks with a 50

characteristic impedance.
The characteristic impedance depends on the dielectric, the track width and the
ground plane spacing.