User's Manual

Telit GM862-QUAD/-QUAD-PY

Hardware User Guide

1vv0300692, Rev. ISSUE#0, - 04/10/2005

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 100μF 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: