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Telit GM862-QUAD/-QUAD-PY
Hardware User Guide
1vv0300692, Rev. ISSUE#0, - 04/10/2005
Reproduction forbidden without DAI Telecom written authorization – All Right reserved – Right of modification reserved
page 11 of 69
3.2.1.2 + 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 GM862-QUAD.
•
When using a switching regulator, a 500Khz 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.
•
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 100
μ
F 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.
•
For Car applications a spike protection diode should be inserted close to the power input, in
order to clean the supply from spikes.
•
A protection diode should be inserted close to the power input, in order to save the GM862-
QUAD from power polarity inversion. This can be the same diode as for spike protection.
An example of switching regulator with 12V input is: