User's Manual
LE910 V2 HARDWARE USER GUIDE 1VV0301200 Rev.2 Preliminary • 2015-08-04 27 of 81
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4.3.1.5 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 on the input to protect the supply from spikes The placement of this component 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 LE910 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 LE910 V2 is wide enough to ensure a dropless connection even during
an 0.8 A current peak.
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 an 2 A current peak is absorbed (worst case of GSM mode).
The PCB traces to the LE910 V2 and the Bypass capacitor must be wide enough to ensure no significant
voltage drops occur. This is for the same reason as previous point. Try to keep this trace as short as
possible.
To reduce the EMI due to switching, it is important to keep very small the mesh involved; thus the input
capacitor, the output diode (if not embodied in the IC) and the regulator have to form a very small loop.This
is done in order to reduce the radiated field (noise) at the switching frequency (100-500 kHz usually).
A dedicated ground for the Switching regulator separated by the 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.
The insertion of EMI filter on VBATT pins is suggested in those designs where antenna is placed close to
battery or supply lines. A ferrite bead like Murata BLM18EG101TN1 or Taiyo Yuden P/N
FBMH1608HM101 can be used for this purpose.