Network Hardware User Manual

UC864-E Hardware User Guide

1vv0300766a Rev.1 - 31/01/08

An example of linear regulator with 5V input is:

5.2.1.2 + 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 UC864-E.

• 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.

• 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. The same

consideration has to be applied to the voltage peaks that in a Car Application could rise to 100V.

• 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.

• A spike protection diode should be inserted close to the power input for Car applications, in order

to clean the supply from spikes.

• A protection diode should be inserted close to the power input, in order to save UC864-E from

power polarity inversion. This can be the same diode as for spike protection.