Telit Wireless Solutions GL865 V3, Руководство пользователя

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HW User Guide
1vv0301018 Rev. 15 Page 29 of 72 2019-01-07
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 V3/V3.1
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 V3/V3.1 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 V3/V3.1, then this
noise is not so disturbing and power supply layout design can be more forgiving.
• The PCB traces to the GL865 V3/V3.1 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.