User's Guide

UC864-E-AUTO / AWS-AUTO Hardware User Guide
1vv0300795 Rev.11 – 2010/11/18
Reproduction forbidden without Telit Communications S.p.A’s. written authorization - All Rights Reserved. Page 24 of 78
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 three categories:
• +5V input (typically PC internal regulator output)
• +12V input (typically automotive)
• battery
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 UC864-E-AUTO / AWS-
AUTO, 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 UC864-E-AUTO / AWS-AUTO from power polarity inversion.