Telit Wireless Solutions CE910-DC, Руководство пользователя по оборудованию

Страница: 31 / 67

An example of a linear regulator with 5V input:

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 suitable and must not be
used. A switching power supply would be preferable because of its better efficiency,
especially with the 1A peak current load represented by CE910.

When using a switching regulator, a 500 kHz 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 must 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 tantalum capacitor is usually suited for this.

Make sure the low ESR capacitor on the power supply output (usually a tantalum one) is
rated at least 10V.

For car applications a spike protection diode must be inserted close to the power input in
order to clean the supply from spikes.

A protection diode must be inserted close to the power input in order to save the CE910
from power polarity inversion. This can be the same diode as for spike protection.