ASDL-3023 datasheet(18/26 Pages) LITEON

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Appendix B: PCB Layout Suggestion

TheeffectsofEMIandpowersupplynoisecanpotentially

reducethesensitivityofthereceiver,resultinginreduced

linkdistance.ThePCBlayoutplayedanimportantroleto

obtainagoodPSRRandEMimmunityresultingingood

electricalperformance.Thingstonote:

1. The ground plane should be continuous under the

part,butshouldnotextendundertheshieldtrace.

2. Theshieldtraceisawide,lowinductancetraceback

tothesystemground.CX1,CX2,CX3,CX4andCX5are

optionalsupplyfiltercapacitors;theymaybeleftoutif

acleanpowersupplyisused.

3. VLED can be connected to either unfiltered or

unregulated power supply. The bypass capacitors

should be connection before the current limiting

resistor R2 respectively. In a noisy environment,

including capacitor CX3and CX4 can enhance supply

rejection.CX3thatisgenerallyaceramiccapacitorof

lowinductanceprovidingawidefrequencyresponse

whileCX4istantalumcapacitorofbigvolumeandfast

frequency response.The use of a tantalum capacitor

ismorecriticalontheVLEDline,whichcarriesahigh

current.

4. VCC pin can be connected to either unfiltered or

unregulated power supply.The Resistor, R1 together

withthecapacitors,CX1andCX2actsasthelowpass

filter.

5. IOVCC is connected to the ASIC voltage supply or

theVCCsupply.Thecapacitor,CX5actsasthebypass

capacitor.

6. Preferably a multi-layered board should be used

to provide sufficient ground plane. Use the layer

underneath and near the transceiver module as Vcc,

and sandwich that layer between ground connected

board layers. The diagram below demonstrate an

exampleofa4layerboard:

• TopLayer:

Connectthemetalshieldand

modulegroundpintobottom

groundlayer;

Placethebypasscapacitorswithin

0.5cmfromtheVCCandground

pinofthemodule.

• Layer2:

Criticalgroundplanezone.3

cminalldirectionaroundthe

module.Connecttoaclean,

noiselessgroundnode(eg

bottomlayer).

• Layer3:

Keepdatabusawayfromcritical

groundplanezone.

• Bottomlayer:

Groundlayer.Groundnoise<75

mVp-p.Shouldbeseparatedfrom

groundusedbynoisysources.

Theareaunderneaththemoduleatthesecondlayer,and

3cminalldirectionaroundthemoduleisdefinedasthe

criticalgroundplanezone.Thegroundplaneshouldbe

maximizedinthiszone.RefertoapplicationnoteAN1114

ortheAvagoTechnologiesIrDADataLinkDesignGuide

fordetails.Thelayoutbelowisbasedona2-layerPCB.

Top Layer

Bottom Layer

Layer 3

Top Layer

Layer 2

Bottom Layer (GND)

Noise sources to be placed as far away from the transceiver as possible

Legend: ground via

CX3

CX4

CX1

CX2

CX5

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