Telit Wireless Solutions UC864 manual General Design Rules, Electrical Design Guidelines

UC864-E Hardware User Guide

1vv0300766a Rev.1 - 31/01/08

5.2General Design Rules

The principal guidelines for the Power Supply Design embrace three different design steps:

•The electrical design

•The thermal design

•The PCB layout.

5.2.1 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

5.2.1.1 + 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 UC864-E, 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 electrical circuit from power polarity inversion.

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