User's Manual

GL865 Hardware User Guide

1vv0300910 Rev.1 – 2011-07-22

page 25 of 79

NOTE:

The electrical design for the Power supply should be made

ensuring it will be capable of a peak current output of at least

2 A.

6.3. General Design Rules

The principal guidelines for the Power Supply Design embrace

three different design steps:

• the electrical design

• the thermal design

• the PCB layout.

6.3.1. Electrical Design Guidelines

The electrical design of the power supply depends strongly from

the power source where this power is drained. We will

distinguish them into three categories:

• +5V input (typically PC internal regulator output)

• +12V input (typically automotive)

• Battery

6.3.1.1. + 5V input Source Power Supply Design Guidelines

The desired output for the power supply is 3.8V, hence there's

not a big difference between the input source and the desired

output and a linear regulator can be used. A switching power

supply will not be suited because of the low drop out

requirements.

When using a linear regulator, a proper heat sink shall be

provided in order to dissipate the power generated.

A Bypass low ESR capacitor of adequate capacity must be provided

in order to cut the current absorption peaks close to the GL865,

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.

A protection diode should be inserted close to the power input,

in order to save the GL865 from power polarity inversion.