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This document is the sole and exclusive property of WAVECOM. Not to be distributed or divulged
without prior written agreement.
WM_PRJ_Q24NG_PTS_002-001 June
2006
3.1.3
PCB routing constraints
3.1.3.1 Power supply routing Constraints
•
A ground plane must be provided on the PCB. This plane must not
be parceled out.
•
Attention shall be paid to the power supply tracks and to the ground
plane which supply the module. The tracks and the plane used must
support current peaks.
•
Since the maximum peak current can reach 1.5A MAX, Wavecom
strongly recommends a large width for the layout of the power
supply signal (to avoid voltage loss between the external power
supply and the module supply. Filtering capacitors, near the module
power supply, could also be added (refer to section 3.1.3.3).
•
The routing must be done in such a way that the total impedance
line is
≤
10 m
Ω
@ 217 Hz. This impedance must include the via
impedances.
•
Same care shall be taken when routing the ground supply.
•
If these design rules are not followed, phase error (peak) and power
loss could occur.
3.1.3.2 Application ground plane and shielding connection
The grounding connection is done through the shielding
the four legs
have to be soldered to the ground plane (
see Wavecom recommendation
for lead free soldering in Section 6.3).
A ground plane must be available on the application board to provide
efficient connection to the Q24NG shielding.
Best shielding performance will be achieved if the application ground plane
is a complete layer of the application PCB:
•
To ensure a good shielding of the module, a complete ground plane
layer must be available, with no trade-off. Connections between
other ground planes shall be made with vias.
•
Without this ground plane, external Tx spurious or Rx blockings
could appear.
Warning:
It is strongly recommended to avoid routing any signals under the Q24NG.
3.1.3.3 Decoupling of power supply signals
Decoupling capacitors on VBATT and VDD lines are embedded in the
module. So it should not be necessary to add decoupling capacitors close
to the module.
However, in case of EMI/RFI problem, some signals like VBATT and charge
line (CHG_IN) may require some EMI/RFI decoupling: parallel 33 pF
capacitor close to the module or a serial ferrite bead (or both to get better
results).
