August 2004 M9999-081304 [email protected]or (408) 955-1690 1:2 Differential PECL/LVPECL/ECL Fanout Buffer SY89311U Evaluation Board General Description The SY89311U evaluation board is designed for convenient setup and quick evaluation of the SY89311U. It allows the user to evaluate the part over the full voltage range of the part. The evaluation board standard configuration is AC- coupled for direct interface to a 50Ω compatible oscilloscope without split supplies. For applications that require a DC-coupled configuration, step-by-step instructions for modifying the board are included. The board is fully assembled and tested and is accompanied with all necessary documentation. Data sheets and support documentation can be found on Micrel’s web site at www.micrel.com. Features • SY89311U • Single +2.5V, +3.3V or +5V power supply • AC-coupled configuration for ease-of-use • I/O Interface Includes on-board termination • Fully assembled and tested • Can be reconfigured for DC-coupled operation Related Documentation • SY89311U, 2.5V/3.3V/5V 1:2 Differential PECL/LVPECL/ECL Fanout Buffer Data Sheet ____________________________________________________________________________________ Evaluation Board
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General DescriptionThe SY89311U evaluation board is designed forconvenient setup and quick evaluation of theSY89311U. It allows the user to evaluate the partover the full voltage range of the part.The evaluation board standard configuration is AC-coupled for direct interface to a 50Ω compatibleoscilloscope without split supplies. For applicationsthat require a DC-coupled configuration, step-by-stepinstructions for modifying the board are included.The board is fully assembled and tested and isaccompanied with all necessary documentation.Data sheets and support documentation can be foundon Micrel’s web site at www.micrel.com.
Features• SY89311U• Single +2.5V, +3.3V or +5V power supply• AC-coupled configuration for ease-of-use• I/O Interface Includes on-board termination• Fully assembled and tested• Can be reconfigured for DC-coupled operation
Related Documentation• SY89311U, 2.5V/3.3V/5V 1:2 Differential
Evaluation Board DescriptionThe SY89311U evaluation board is initially configuredfor +3.3V operation. The board can be easily modifiedfor +2.5V or +5V operation.The default configuration for the board is the AC-coupled configuration and all boards are shipped withthis configuration. The choice between twoconfigurations offers the user flexibility in selecting theboard that is right for his particular application.AC-Coupled Evaluation BoardThe AC-coupled configuration is suited to mostcustomer applications and is preferred by the majorityof users because of its ease-of-use. It requires only asingle power supply and offers the most flexibility ininterfacing to a variety of signal sources.The DC-bias levels and AC-coupling capacitors aresupplied on-board for each input, making itunnecessary to vary the offset voltage or change anycomponents on the board as the power supplyvoltage varies over the +3.3V +10% operating range.The user needs only to supply a minimum inputvoltage swing and the bias voltage will automaticallyadjust the input to the correct level as the powersupply voltage varies.To modify the +3.3V AC-coupled evaluation boardinto a +2.5V or +5V AC-coupled evaluation board,resistor values for R9, R10, R11 and R12 at theinputs and R2, R4, R6 and R8 at the outputs need tobe changed as shown in the following table.
VCC R2-R8 R9/R11 R10/R12
2.5V 82Ω 104Ω 96Ω
3.3V 82Ω 82Ω 130Ω
5.0V 180Ω 68Ω 192Ω
Table 1. Resistor Values
DC-Coupled Evaluation BoardFor DC-coupled operation, the board can be modifiedto use two power supplies in a “split-supplyconfiguration.” The term split-supply simply meansthe +3.3V supply is split into a +2V and –1.3V, the+2.5V supply is split into a +2V and –0.5V, or for a+5V supply it is split into a +2V and –3V power supplyconfiguration. This effectively offsets the board by+2V. The +2V offset in this two-power supplyconfiguration then provides the correct terminationsfor the device by setting the Ground potential on theboard to be exactly 2 volts below the VCC supply. TheVEE voltage is then set to the appropriate negativevoltage so the device power pins still see a full 2.5V,3.3V or 5V potential between VCC and VEE.Step-by-step instructions for modifying an AC-coupledevaluation board for DC-coupled operation aresupplied in the “Modifying your AC-Coupled Board forDC-Coupled Operation” section.
AC-Coupled Evaluation Board SetupSetting Up the AC-coupled Evaluation BoardThe following steps describe the procedure for settingup the evaluation board:
1. Set the voltage setting for a DC supply to beeither 3.3V or 5.0V depending on yourapplication and turn off the supply.
2. Connect the GND terminal to the negativeside of a DC power supply. This is the 0Vground potential.
3. Connect the VCC terminal to the positive sideof a DC power supply
4. Turn on the power supply and verify that thepower supply current is <100mA.
5. Turn off the power supply.6. Using a differential signal source set the
amplitude of each side of the differential pairto be 800mV (1600mV measureddifferentially). Set the offset to be a positivevalue, the value of this offset is not critical,as the AC-coupled inputs will beautomatically biased to the correct offset.Turn off or disable the outputs of the signalsource.
7. Using equal length 50Ω impedance coaxialcables, connect the signal source to theinputs on the evaluation board (SMA2 andSMA3).
8. Using equal length 50Ω impedance coaxialcables, connect the outputs of the evaluationboard (SMA1, SMA2, SMA3 and SMA4) tothe oscilloscope or other measurementdevice that has an internal 50Ω termination.
9. Turn on the power and verify the current is<100mA.
10. Enable the signal source and monitor theoutputs.
Evaluation Board LayoutPC Board LayoutThe evaluation boards are constructed with Rogers4003 material and are coplanar in design fabricatedto minimize noise, achieve high bandwidth andminimize crosstalk.
Modifying DC-Coupled Outputsfor AC-Coupled OperationWhen DC-coupling is NecessaryFor applications where AC-coupling is notappropriate, the board can be reconfigured for DC-coupled operation. An example where DC-coupling isrequired is if the input data or clock can be disabled.This would result in a DC-signal at the inputs and theon-board biasing resistors (R9, R10, R11 and R12)would apply the same level to both the true andcomplement inputs. Since these inputs are differentialthis would result in an intermediate non-differentialstate at the inputs and the outputs would be in anindeterminate condition. Reconfiguring the board forDC-coupled operation and using two power suppliescan avoid this condition.Reconfiguring an AC-Coupled Board into a DC-Coupled BoardThe following procedure details the steps forconverting an AC-coupled board to a DC-coupledboard:
2. Add in resistors R17 and R18 as shown inthe loading diagram.
3. Replace capacitors C1, C2, C3 and C4, C5and C6 with 0Ω resistors.
4. Remove the soldered-wire shorting barbetween J2 (VEE) and the ground plane.
5. Install components J2, C11 and C12. Theselocations should look like the components inJ3, C9 and C10.
6. For easy identification, remove the solderdot from the adjacent AC-coupled silkscreenlabel on the front of the board and add asolder dot to the DC-coupled.
Setting Up the DC-coupled Evaluation BoardThe follow steps describe the procedure for setting upthe DC-coupled evaluation board:
1. Set the voltage for DC supply number 1 tobe 2.0V and connect it to J3 (VCC).
2. Set the voltage for DC supply number 2 tobe –1.3V (for 3.3V operation), –0.5V (for2.5V operation) or –3.0V (for 5.0V operation)and connect it to J3 (VEE).
3. Connect the negative side of power supply 1to the positive side of power supply 2. Thisis the 0V ground potential for the board.
4. Turn off the power supplies and connect theGND terminal on the board to the negativeside of a DC power supply 1 and the positiveside of DC power supply 2
5. Turn on the power supply and verify that thepower supply current is <100mA. Using avoltmeter.
6. Turn off the power supply.7. Disable the outputs of the differential signal
source and set the VOH = VCC–1.0V and theVOL = VCC–1.75V) as shown in the followingtable.
8. Using equal length 50Ω impedance coaxialcables, connect the signal source to theinputs on the evaluation board (SMA6 andSMA7).
9. Using equal length 50Ω impedance coaxialcables, connect the outputs of the evaluationboard (SMA1, SMA2, SMA3 and SMA4) tothe oscilloscope or other measurementdevice that has an internal 50Ω termination.
10. Turn on the power and verify the current is<100mA.
11. Enable the signal source and monitor theoutputs.
Application Hints and NotesFor application notes on high speed termination onPECL and LVPECL products, clock synthesizerproducts, SONET jitter measurement, and other HighBandwidth product go to Micrel Semiconductorswebsite at http://www.micrel.com/. Once in Micrel’swebsite, follow the steps below:
1. Click on “Product Info”.2. In the Applications Information Box, choose
“Application Hints and Application Notes.
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