Telit Wireless Solutions HE910-EU V2, Руководство пользователя по оборудованию

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conducted to the ground plane under the HE910 V2; you must ensure that your application
can dissipate heat.
In the WCDMA/HSPA mode, since HE910 V2 emits RF signals continuously during
transmission, you must pay special attention how to dissipate the heat generated.
The current consumption will be up to about 640mA in HSPA (630mA in WCDMA)
continuously at the maximum TX output power (23dBm). Thus, you must arrange the PCB
area as large as possible under HE910 V2 which you will mount. You must mount HE910 V2
on the large ground area of your application board and make many ground vias to dissipate
the heat.
The peak current consumption in the GSM mode is higher than that in WCDMA. However,
considering the heat sink is more important in case of WCDMA.
As mentioned before, a GSM signal is bursty, thus, the temperature drift is more insensible
than WCDMA. Consequently, if you prescribe the heat dissipation in the WCDMA mode,
you don’t need to think more about the GSM mode.
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 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 HE910 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 if the PCB trace from the capacitor to
HE910 V2 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 no voltage drops to 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 (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 audio interface but only uses the data feature of
the Telit HE910 V2, then this noise is not so disturbing and power supply layout
design can be more forgiving.

The PCB traces to HE910 V2 and the Bypass capacitor must be wide enough to
ensure no significant voltage drops to occur when the 2A current peaks are
absorbed. This is a must for the same above-mentioned reasons. Try to keep this
trace as short as possible.