User's Manual

CL865-DUAL Hardware User Guide
1vv0301104 Rev.1 – 2014-03-07
Reproduction forbidden without written authorization from Telit Communications S.p.A. - All Rights
Reserved. Page 26 of 70
Mod. 0805 2011-07 Rev.2
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 on the power source from which
this power is drained. We will distinguish them into three categories:
 +5V input (typically PC internal regulator output)
 +12V input (typically automotive)
 Battery
6.3.2. + 5V Input Source Power Supply Design Guidelines
 The desired output for the power supply is 3.8V, hence there is not a big
difference between the input source and the desired output so a linear regulator
can be used. A switching power supply will not be suitable because of the low
drop-out requirements.
 When using a linear regulator, a proper heat sink must 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 CL865. A 100μF 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 must be inserted close to the power input in order to save the
CL865 from power polarity inversion.