User guide

UC864-E/G/WD/WDU Hardware User Guide

1vv0300766a Rev.4

- 03/02/09

WCDMA 775 WCDMA data channel

HSDPA 825 HSDPA data channel

GSM TX and RX mode with GPS ON full

power mode*

GSM Voice 410 GSM voice channel

GPRS Class12 880 GPRS data channel

EDGE Class12 650 EDGE data channel

* except external active GPS antenna

In GSM/GPRS mode, RF transmission is not continuous and it is packed into bursts

at a base frequency of about 216 Hz, and the relative current peaks can be as high

as about 2A. Therefore the power supply has to be designed in order to withstand

these current peaks without big voltage drops; this means that both the electrical

design and the board layout must be designed for this current flow. If the layout of the

PCB is not well designed, a strong noise floor is generated on the ground; this will

reflect on all the audio paths producing an audible annoying noise at 216 Hz; if the

voltage drops during the peak, current absorption is too much. The device may even

shut down as a consequence of the supply voltage drop.

5.2. 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

5.2.1. Electrical Design Guidelines

The electrical design of the power supply depends strongly on 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

TIP:

The electrical design for the Power supply must be made ensuring that it will be

capable of a peak current output of at least 2A.