SAA5265 Просмотр технического описания (PDF) - Philips Electronics

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SAA5265

10 and 1 page intelligent teletext decoders

Philips Electronics 

Philips Semiconductors

10 and 1 page intelligent teletext decoders

Preliminary specification

SAA5264; SAA5265

EMC GUIDELINES

Optimization of circuit return paths and minimization of

common mode emission will be assisted by using a double

sided Printed Circuit Board (PCB) with low inductance

ground plane.

On a single-sided PCB a local ground plane under the

whole IC should be present as shown in Fig.3. This should

have the widest possible connection between the PCB

ground and bulk electrolytic decoupling capacitor.

Preferably, the PCB local ground plane connection should

not be connected to other grounds on route to the PCB

ground. Do not use wire links. Wire links cause ground

inductance which increases ground bounce.

The supply pins can be decoupled at the ground pin plane

below the IC. This is easily achieved by using surface

mount capacitors, which, at high frequency, are more

effective than components with leads.

Using a device socket would increase the area and

therefore increase the inductance of the external bypass

loop.

To provide a high-impedance to any high frequency

signals on the VDD supplies to the IC, a ferrite bead or

inductor can be connected in series with the supply line

close to the decoupling capacitor. To prevent signal

radiation, pull-up resistors of signal outputs should not be

connected to the VDD supply on the IC side of the ferrite

bead or inductor.

OSCGND should only be connected to the crystal load

capacitors and not to any other ground connection.

Distances to physical connections of associated active

devices should be as short as possible.

PCB output tracks should have close proximity, mutually

coupled, ground return paths.

handbook, full pagewidth

other

GND

connections

under-IC GND plane

GND connection

note: no wire links

GND +3.3 V

electrolytic decoupling capacitor (2 µF)

ferrite beads

SM decoupling capacitors (10 to 100 nF)

under-IC GND plane

VSSC

VSSA

IC

MBK979

2000 Jan 27

Fig.3 Power supply connections for EMC.

15

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