User's Manual

GE864
GE864GE864
GE864-
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-QUAD Automotive V2 Hardware User Guide
QUAD Automotive V2 Hardware User GuideQUAD Automotive V2 Hardware User Guide
QUAD Automotive V2 Hardware User Guide
1vv0300840 Rev.3 2010-04-08
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved page 30 of 71
6.3.3.
6.3.3.6.3.3.
6.3.3. Power Supply PCB layout Guidelines
Power Supply PCB layout GuidelinesPower Supply PCB layout Guidelines
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 performances.
• The Bypass low ESR capacitor must be placed close to the Telit GE864-QUAD
Automotive V2 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 GE864-QUAD Automotive V2 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
216 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 GE864-QUAD Automotive V2, then this noise is not so disturbing and
power supply layout design can be more forgiving.
• The PCB traces to the GE864-QUAD Automotive V2 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.