Integration Manual

TOBY-L2 and MPCI-L2 series - System Integration Manual
UBX-13004618 - R26 Design-in
Page 82 of 162
2.2.1.9 Guidelines for VCC or 3.3Vaux supply layout design
Good connection of the module VCC or 3.3Vaux pins with DC supply source is required for correct RF
performance. Guidelines are summarized in the following list:
 All the available VCC / 3.3Vaux pins must be connected to the DC source
 VCC / 3.3Vaux connection must be as wide as possible and as short as possible
 Any series component with Equivalent Series Resistance (ESR) greater than few milliohms must be avoided
 VCC / 3.3Vaux connection must be routed through a PCB area separated from RF lines / parts, sensitive analog
signals and sensitive functional units: it is good practice to interpose at least one layer of PCB ground between
the VCC / 3.3Vaux track and other signal routing
 Coupling between VCC / 3.3Vaux and digital lines, especially USB, must be avoided.
 The tank bypass capacitor with low ESR for current spikes smoothing described in section 2.2.1.6 should be
placed close to the VCC / 3.3Vaux pins. If the main DC source is a switching DC-DC converter, place the large
capacitor close to the DC-DC output and minimize VCC / 3.3Vaux track length. Otherwise consider using
separate capacitors for DC-DC converter and module tank capacitor
 The bypass capacitors in the pF range described in Figure 37 and Table 25 should be placed as close as possible
to the VCC / 3.3Vaux pins. This is highly recommended if the application device integrates an internal antenna
 Since VCC / 3.3Vaux input provide the supply to RF Power Amplifiers, voltage ripple at high frequency may
result in unwanted spurious modulation of transmitter RF signal. This is more likely to happen with switching
DC-DC converters, in which case it is better to select the highest operating frequency for the switcher and
add a large L-C filter before connecting to the TOBY-L2 and MPCI-L2 series modules in the worst case
 If VCC / 3.3Vaux is protected by transient voltage suppressor to ensure that the voltage maximum ratings are
not exceeded, place the protecting device along the path from the DC source toward the module, preferably
closer to the DC source (otherwise protection functionality may be compromised)
2.2.1.10 Guidelines for grounding layout design
Good connection of the module GND pins 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 VCC supply current flows back to main DC source through GND as ground current: provide adequate
return path with suitable uninterrupted ground plane to main DC source
 It is recommended to implement one layer of the application board as ground plane as wide as possible
 If the application board is a multilayer PCB, then all the board layers should be filled with GND plane as much
as possible and each GND area should be connected together with complete via stack down to the main
ground layer of the board. Use as many vias as possible to connect the ground planes
 Provide a dense line of vias at the edges of each ground area, in particular along RF and high speed lines
 If the whole application device is composed by more than one PCB, then it is required to provide a good and
solid ground connection between the GND areas of all the different PCBs
 Good grounding of GND pads also ensures thermal heat sink. This is critical during connection, when the real
network commands the module to transmit at maximum power: proper grounding helps prevent module
overheating.