User's Guide

HE863 Family Hardware User Guide
1vv0300891 Rev.5
- 2011-03-18
Reproduction forbidden without Telit Communications S.p.A’s. written authorization - All Rights
Reserved. Page 40 of 89
6.2. 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
6.2.1. Electrical Design Guidelines
The electrical design of the power supply depends strongly on
the power source where this power is drained. We will
distinguish them into two categories:
 +5V input (typically PC internal regulator output)
 +12V input (typically automotive)
6.2.1.1. + 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 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 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 HE863 Family, 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 HE863 Family from power
polarity inversion.