Telit Communications S.p.A. GC864Q2 ユーザーズマニュアル

GC864 Hardware User Guide

1vv0300874 Rev.0 – 2010-01-25

Page 25 of 64

6.2.1.2.

+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 especially with the 2A
peak current load represented by the GC864-QUAD V2 / GC864-DUAL V2.

• 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 that the switching frequency
could also generate EMC interferences.

• As far as car PB battery, the input voltage can rise up to 15.8V. 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
typically used.

• Make sure the low ESR capacitor on the power supply output (usually a

tantalum one) is rated at least 10V.

• As far as 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 can be inserted close to the power input, in order to

save the GC864-QUAD V2 / GC864-DUAL V2 from power polarity inversion.
This can be the same diode used for spike protection.