SC14CVMDECT datasheet(47/57 Pages) DIALOG

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Datasheet

Revision 3.0

28-Jul-2015

CFR0011-120-00-FM Rev 5

47 of 57

SC14CVMDECT SF

Cordless Voice Module

FINAL

For an FP hardware design the following hardware

parts will be needed besides the SC14CVMDECT SF:

• Supply voltage

• Battery charge

• LED and buttons

• Audio:

• Headset

• External PCM device.

For a PP hardware design the following hardware parts

will be needed besides the SC14CVMDECT SF:

• Power

• Battery Charger

• Audio:

• Microphone

• Earpiece

• Speaker

• Headset

8.3.2 PCB Design Guidelines

• Because of the presence of the digital radio fre-

quency burst with 100 Hz time division periods (TDD

noise), supply ripple and RF radiation, special atten-

tion is needed for the power supply and ground PCB

layout.

• Power supply considerations

Both high and low frequency bypassing of the supply

line connections should be provided and placed as

close as possible to the SC14CVMDECT SF. In

order to get the best overall performance for both FP

and PP applications, a number of considerations for

the PCB has to be taken into account.

• Make angle breaks on long supply lines to avoid

resonance frequencies in respect to DECT fre-

quencies. Maximum 8 cm before an angle break

is recommended.

• Supply lines should be placed as far as possible

away from sensitive audio circuits. If it is neces-

sary to cross supply lines and audio lines, it

should be done with right angles between supply

and audio lines/circuits (microphone, ear-speaker,

speakerphone, etc.)

• Ground plane considerations

In order to achieve the best audio performance

and to avoid the influence of power supply noise,

RF radiation, TDD noise and other noise sources,

it is important that the audio circuits on both FP

and PP applications boards are connected to the

VREFM pin (analog ground: AGND, see Figure

38) on the SC14CVMDECT SF with separate nets

in the layout.

It is advised to provide the following audio circuits

with separate ground nets connected to the

VREFM pin:

• Microphone(s)

• Headset microphone and speaker

• Speakerphone (signal grounds)

Depending on the layout it may also be necessary to

bypass a number of the audio signals listed above to

avoid humming, noise from RF radiation and TDD

noise with. It is also important to choose a microphone

of appropriate quality with a high RF immunity (with

built-in capacitor).

• ESD performance

Besides TDD noise, the ESD performance is impor-

tant for the end-application. In order to achieve a

high ESD performance supply lines should be

placed with a large distance from charging terminals,

display, headset connector and other electrical ter-

minals with direct contact to the ESD source.

On a two-layer PCB application it is important to

keep a simulated one layer ground. With a stable

ground ESD and TDD noise performance will always

improve.

• Clearance around test patterns

Pin number 81 to 88 are used for production test

purposes. In order to avoid any interference or dis-

turbance the area around these signal pins must be

kept clear of any signal and/or GND. The recom-

mended clearance is at least 1 mm as shown in Fig-

ure 36.

Figure 36: Clearance around test patterns

Test

pattern

0.9mm

1.0mm

GND Pattern

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