User's Guide

UC864-E-AUTO / AWS-AUTO Hardware User Guide

1vv0300795 Rev.11 – 2010/11/18

An example of linear regulator with 5V input is:

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 must not be used. A switching power supply

will be preferable because of its better efficiency especially with the 2A

peak current load represented by UC864-E-AUTO / AWS-AUTO.

• 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 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.