Integration Manual

TSD-19090601 - R15 Contents Page 73 of 143
noise rejection in the band centered on the Self-Resonant Frequency of the pF capacitors. This is highly
recommended if the application device integrates an internal antenna.
 Since VCC input provides the supply to the RF Power Amplifiers, any voltage ripple at high frequency
may result in unwanted spurious modulation of the 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-L3 series modules in the worst
case.
 Shielding of switching DC-DC converter circuit, or at least the use of shielded inductors for the switching
DC-DC converter, may be considered since all switching power supplies may potentially generate
interfering signals as a result of high-frequency high-power switching.
 If the VCC is protected by a 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 close to the DC source, otherwise protection functionality may be affected.
2.2.1.11 Guidelines for grounding layout design
A clean connection of the module GND pins with the 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 the application board solid GND layer. It is strongly recommended that
each GND pad surrounding the VCC pins has one or more dedicated via down to the application board
solid ground layer.
 The VCC supply current flows back to the main DC source through GND as the ground current: provide
an adequate return path with suitable uninterrupted ground plane to the main DC source.
 It is recommended to design one layer of the application PCB as a 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 a complete via stack down to
the main ground layer of the board.
 If the whole application device is composed of more than one PCB, then it is required to provide a good
and solid ground connection between the GND areas of all the multiple PCBs.
 Good grounding of the GND pads also ensures the thermal heat sink. This is critical during connection,
when the real network commands the module to transmit at maximum power: correct grounding helps
prevent module overheating.
2.2.2 Generic digital interfaces supply output (V_INT)
2.2.2.1 Guidelines for V_INT circuit design
TOBY-L3 series provide the V_INT generic digital interfaces 1.8 V supply output, which can be mainly used
to:
 Indicate when the module is switched on (as described in sections 1.6.1, 1.6.2)