LE910Cx mPCIe Hardware Design Guide
1VV0301510 Rev. 13 Page 24 of 73 2021-07-07
The area to which the thermal pad is attached to on the application board must be
designed as a large ground pad (with solder mask exposed).
4.3.3. Power Supply PCB Layout Guidelines
The GSM system is made in a way that the RF transmission is not continuous, otherwise
it is packed into bursts at a base frequency of about 216 Hz, and the relative current peaks
can be as high as about 2.4A. Therefore the power supply must be designed in such a way
to withstand with these current peaks without large voltage drops; this means that both
the electrical design and the board layout must be designed for this current flow. If the
voltage drop during the peak current absorption is too much, then the device may even
shutdown as a consequence of the drop in the supply voltage.
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 performance
of the power supply.
• The Bypass low ESR capacitor must be placed close to the Telit LE910Cx-mPCIe
power input pads or if the power supply is of the switching type it can be placed
near the inductor to cut the ripple provided the PCB trace from the capacitor to
the LE910Cx-MPCIE is wide enough to ensure a dropless connection even during
an 1A 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 a 1A current peak is absorbed.
: The average consumption during transmissions depends on
the power level at which the device is requested to transmit by the
network. The average current consumption therefore varies
significantly.
: The electrical design for the Power supply should be made
ensuring it will be capable of a peak current output of at least 2.4 A.
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