L
LE920 Hardware User Guide
1vv0301026 Rev.0 - draft4 – 2013-05-
Reproduction forbidden without written authorization from Telit Communications S.p.A. - All Rights Reserved.
Page 36 of 76
An example of linear regulator with 5V input is:
5.2.1.2.
+ 12V Input Source Power Supply Design Guidelines
x
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 must not be used. A switching power supply will be preferable because of its
better efficiency especially with the 2A peak current load represented by LE920.
x
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.
x
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.
x
For car PB battery the input voltage can rise up to 15.8V and this must be kept in
mind when choosing components: all components in the power supply must
withstand this voltage.
x
A Bypass low ESR capacitor of adequate capacity must be provided in order to
s usually suited for
this.
x
Make sure the low ESR capacitor on the power supply output (usually a tantalum
one) is rated at least 10V.
x
For Car applications a spike protection diode must be inserted close to the power
input, in order to clean the supply from spikes.
x
A protection diode must be inserted close to the power input, in order to save
LE920 from power polarity inversion. This can be the same diode as for spike
protection.
