LE910C1
Hardware User Guide
1VV0301298 Rev. 1.08 - 2017-11-14
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Telit Confidential Information, provided under NDA
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63 of 119
6.2.3.
Power Supply PCB Layout Guidelines
As seen in the electrical design guidelines, the power supply must 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
operation 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 LE910C1 power input pads, or if
the power supply is of a switching type, it can be placed close to the inductor to cut the
ripple, as long as the PCB trace from the capacitor to LE910C1 is wide enough to ensure a
drop-less 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 that no voltage drops occur during the 2A current peaks.
Note that this is not done 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 an audio interface but only uses the data feature of the
LE910C1, this noise is not so disturbing, and the power supply layout design can be more
forgiving.
•
The PCB traces to LE910C1 and the bypass capacitor must be wide enough to ensure that
no significant voltage drops occur when the 2A current peaks are absorbed. This is needed
for the same above-mentioned reasons. Try to keep these traces 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 the switching power supply). This is done to reduce the
radiated field (noise) at the switching frequency (usually 100-500 kHz).
•
Use a good common ground plane.
•
Place the power supply on the board in a way to guarantee that the high current return
paths in the ground plane do not overlap any noise sensitive circuitry, such as the
microphone amplifier/buffer or earphone amplifier.
•
The power supply input cables must be kept separate from noise sensitive lines, such as
microphone/earphone cables.
