User's Manual

GE/GC864-QUAD V2 and GE864-GPS Hardware User Guide
1vv0300915 Rev.2 – 2011-06-15
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights
Reserved. Page 38 of 97
The GSM system is made in a way that the RF transmission is
not continuous, else it is packed into bursts at a base
frequency of about 216 Hz, the relative current peaks can be
as high as about 2A. Therefore the power supply has to be
designed in order to withstand with these current peaks
without big voltage drops; this means that both the electrical
design and the board layout must be designed for this current
flow.
If the layout of the PCB is not well designed a strong noise
floor is generated on the ground and the supply; this will
reflect on all the audio paths producing an audible annoying
noise at 216 Hz; if the voltage drop during the peak current
absorption is too much, then the device may even shutdown as a
consequence of the supply voltage drop.
TIP:
The electrical design for the Power supply should be made
ensuring it will be capable of a peak current output of at
least 2A.
6.3. General Design Rules
The principal guidelines for the Power Supply Design embrace
three different design steps:
• the electrical design
• the thermal design
• the PCB layout.
6.3.1. Electrical Design Guidelines
The electrical design of the power supply depends strongly
from the power source where this power is drained. We will
distinguish them into three categories:
• +5V input (typically PC internal regulator output)
• +12V input (typically automotive)
• Battery
6.3.1.1. +5V input Source Power Supply Design Guidelines
• The desired output for the power supply is 3.8V, hence
there is no big difference between the input source
and the desired output. A linear regulator can be
used. A switching power supply will not be suited
because of the low drop out requirements.