Integration Manual

LISA-U series - System Integration Manual
3G.G2-HW-10002-A3 Preliminary Design-In
Page 114 of 160
 If DC decoupling is required, a large capacitor needs to be used, typically in the microFarad range,
depending on the load impedance, in order to not increase the lower cut-off frequency of its High-Pass RC
filter response
2.2.1.5 Module grounding
Good connection of the module with application board solid ground layer is required for correct RF
performance. It significantly reduces EMC issues and provides a thermal heat sink for the module.
 Connect each GND pin with application board solid GND layer. It is strongly recommended that each GND
pad surrounding VCC pins have one or more dedicated via down to the application board solid ground layer
 The shielding metal tabs are connected to GND, and are a fundamental part of electrical grounding and
thermal heat-sink. Connect them to board solid ground layer, by soldering them on the baseboard using
PCB plated through holes connected to GND net
 If the application board is a multilayer PCB, then it is required to connect together each GND area with
complete via stack down to main board ground layer
 It is recommended to implement one layer of the application board as ground plane
 Good grounding of GND pads will also ensure thermal heat sink. This is critical during call connection, when
the real network commands the module to transmit at maximum power: proper grounding helps prevent
module overheating
2.2.1.6 Other sensitive pins
A few other pins on the LISA-U series modules requires careful layout.
 RTC supply (V_BCKP): avoid injecting noise on this voltage domain as it may affect the stability of sleep
oscillator
 Power-On (PWR_ON): is the digital input to switch-on the LISA-U series modules. Ensure that the voltage
level is well defined during operation and no transient noise is coupled on this line, otherwise the module
might detect a spurious power-on request
2.2.1.7 High-speed digital pins
The following high speed digital pins require careful layout:
 Serial Peripheral Interface (SPI): can be used for high speed data transfer (UMTS/HSPA) between the
LISA-U series modules and the host processor, with a data rate up to 26 Mb/s (see Section 1.9.3). The
high-speed data rate is carried by signals SPI_SCLK, SPI_MISO and SPI_MOSI, while SPI_SRDY and
SPI_MRDY behave as handshake signals with relatively low activity
 Digital Clock Output (CODEC_CLK): can be used to provide a 26 MHz or 13 MHz digital clock to an
external audio codec
Follow these hints for high speed digital pins layout:
 High-speed signals become sources of digital noise, route away from RF and other sensitive analog signals
Keep routing short and minimize parasitic capacitance to preserve digital signal integrity