GE865 Hardware User Guide
1vv0300799 Rev.9 – 27-07-2009
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved
page 26 of 70
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's not a big difference
between the input source and the desired output and a linear regulator can be used. A
switching power supply will not be suited because of the low drop out requirements.
•
When using a linear regulator, a proper heat sink shall be provided in order to dissipate
the power generated.
•
A Bypass low ESR capacitor of adequate capacity must be provided in order to cut the
current absorption peaks close to the GE865, a 100
μ
F tantalum capacitor is usually
suited.
•
Make sure the low ESR capacitor on the power supply output (usually a tantalum one)
is rated at least 10V.
•
A protection diode should be inserted close to the power input, in order to save the
GE865 from power polarity inversion.
