User's Manual

LE940B6 Hardware User Guide

1VV0301331 Rev. 1.8 - 2017-03-15

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Figure 12: Example of Linear Regulator with 5V Input

6.2.1.2. + 12V Input Source Power Supply – Design Guidelines

• The desired output for the power supply is 3.8V. Due to the big difference between the input

source and the desired output, a linear regulator is unsuitable and must not be used. A

switching power supply is preferable because of its better efficiency, especially with the

2A peak current load expected when working with the LE940B6.

• When using a switching regulator, a 500-kHz or higher 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 selection of the frequency and switching design is related to the application

to be developed due to the fact that the switching frequency can also generate EMC

interference.

• For car batteries (lead-acid accumulators) the input voltage can rise up to 15.8V. 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 to cut the current

absorption peaks. A 100μF tantalum capacitor is usually suitable on VBATT & VBATT_PA

power lines.

• Make sure that the low ESR capacitor on the power supply output (usually a tantalum one) is

rated at least 10V.

• For automotive applications, a spike protection diode must be inserted close to the power

input to clean the supply of spikes.

• A protection diode must be inserted close to the power input to protect the LE940B6 module

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