GL865-DUAL V3 Hardware User Guide
1vv0301018 Rev.5 – 2013-08-05
Reproduction forbidden without written authorization from Telit Communications S.p.A. - All Rights Reserved.
Page 30 of 76
Mod. 0805 2011-07 Rev.2
6.3.3.
Power Supply PCB layout Guidelines
As seen on the electrical design guidelines the power supply shall have a low ESR capacitor
on the output to cut the current peaks and a protection diode on the input to protect the supply
from spikes and polarity inversion. The placement of these components is crucial for the
correct working of the circuitry. A misplaced component can be useless or can even decrease
the power supply performance.
•
The Bypass low ESR capacitor must be placed close to the Telit GL865-DUAL V3
power input pads or in the case the power supply is a switching type it can be placed
close to the inductor to cut the ripple provided the PCB trace from the capacitor to the
GL865-DUAL V3 is wide enough to ensure a dropless connection even during the 2A
current peaks.
•
The protection diode must be placed close to the input connector where the power
source is drained.
•
The PCB traces from the input connector to the power regulator IC must be wide
enough to ensure no voltage drops occur when the 2A current peaks are absorbed.
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 approx. 217 Hz that
will reflect on all the components connected to that supply, 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 doesn't have audio
interface but only uses the data feature of the Telit GL865-DUAL V3, then this noise
is not so disturbing and power supply layout design can be more forgiving.
•
The PCB traces to the GL865-DUAL V3 and the Bypass capacitor must be wide
enough to ensure no significant voltage drops occur when the 2A current peaks are
absorbed. This is for the same reason as previous point. 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 (100-500 kHz
usually).
•
The use of a good common ground plane is suggested.
•
The placement of the power supply on the board should be done in such 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 should be kept separate from noise sensitive lines such
as microphone/earphone cables.