User's Guide

HE863 Family Hardware User Guide
1vv0300891 Rev.5
- 2011-03-18
Reproduction forbidden without Telit Communications S.p.A’s. written authorization - All Rights
Reserved. Page 45 of 89
Note that this is not made in order to save power loss
but especially to avoid the voltage drops on the power
line at the current peaks frequency of 216 Hz that
will reflect on all the components connected to that
supply (also introducing the noise floor at the burst
base frequency.) For this reason while a voltage drop
of 300-400 mV may be acceptable from the power loss
point of view, the same voltage drop may not be
acceptable from the noise point of view. If your
application does not have audio interface but only
uses the data feature of the Telit HE863 Family, then
this noise is not so disturbing and power supply
layout design can be more forgiving.
 The PCB traces to HE863 Family and the Bypass
capacitor must be wide enough to ensure no significant
voltage drops to occur when the 2A current peaks are
absorbed. This is a must for the same above-mentioned
reasons. Try to keep this trace as short as possible.
 The PCB traces connecting the Switching output to the
inductor and the switching diode must be kept as short
as possible by placing the inductor and the diode very
close to the power switching IC (only for switching
power supply). This is done in order to reduce the
radiated field (noise) at the switching frequency
(usually 100-500 kHz).
 The use of a good common ground plane is suggested.
 The placement of the power supply on the board must be
done in a way to guarantee that the high current
return paths in the ground plane are not overlapped to
any noise sensitive circuitry as the microphone
amplifier/buffer or earphone amplifier.
 The power supply input cables must be kept separately
from noise sensitive lines such as microphone/earphone
cables.