User's Manual

LE910 V2 HARDWARE USER GUIDE 1VV0301200 Rev.2 Preliminary • 2015-08-04 24 of 81
Reproduction forbidden without Telit Communications PLC written authorization – All Rights Reserved
4.3.1.2 + 12V input Source Power Supply Design Guidelines
The desired output for the power supply is 3.8V, hence due to the big difference between the input source
and the desired output, a linear regulator is not suited and shall not be used. A switching power supply will
be preferable because of its better efficiency.
When using a switching regulator, a 500kHz or more switching frequency regulator is preferable because
of its smaller inductor size and its faster transient response. This allows the regulator to respond quickly
to the current peaks absorption.
In any case the frequency and Switching design selection is related to the application to be developed due
to the fact the switching frequency could also generate EMC interferences.
For car PB battery the input voltage can rise up to 15,8V and this should be kept in mind when choosing
components: all components in the power supply must withstand this voltage.
A Bypass low ESR capacitor of adequate capacity must be provided in order to cut the current absorption
peaks, a 100μF capacitor is usually suited.
Make sure the low ESR capacitor on the power supply output is rated at least 10V.
For Car applications a spike protection diode should be inserted close to the power input, in order to clean
the supply from spikes.
An example of switching regulator with 12V input is in the below schematic: