19-2356; Rev 0; 3/02 MAX3996 Evaluation Kit Features ♦ Drives Common-Anode Lasers The output of the electrical evaluation section is interfaced to an SMA connector that can be connected to a 50Ω terminated oscilloscope. The output of the optical evaluation section is configured for attachment to a laser/monitor diode. ♦ LED Fault Indicator ♦ Fully Assembled and Tested ♦ Adjustable Laser Bias Current ♦ Adjustable Laser Modulation Current ♦ Adjustable Laser Modulation Temperature Coefficient ♦ Configured for Electrical Operation; No Laser Necessary Component Suppliers Ordering Information SUPPLIER AVX PHONE 803-946-0690 FAX 803-626-3123 PART TEMP RANGE Coilcraft 847-639-6400 847-639-1469 MAX3996EVKIT 0°C to +70°C Murata 814-237-1431 814-238-0490 Zetex 516-543-7100 516-864-7630 PINPACKAGE 20 QFN TOP MARK — Component List DESIGNATION QTY C1 1 C2, C3, C7, C9, C10, C15, C16, C21, C26, C44, C48, C49 12 C4, C24 2 DESCRIPTION 0.1µF ±10% 10V ceramic capacitor (0402) 0.01µF ±10% ceramic capacitors (0402) DESIGNATION QTY DESCRIPTION L2, L3, L6 3 Ferrite beads Murata BLM18HG102SN-1 Q1, Q7 2 Transistors Zetex FMMT591A NPN Q3 1 Transistor Zetex FMMT491A PNP R1 1 10kΩ variable resistor 10µF ±10% tantalum capacitors AVX TAJC106K016 R2, R16 2 0Ω resistors (0402) R3 1 Open, user-supplied 1 Open, user-supplied* R4 1 4.3kΩ ±5% resistor (0402) C33 1 0.01µF ±10% ceramic capacitor (0603) R5 1 1kΩ ±5% resistor (0402) 1.8kΩ ±5% resistor (0402) D1 1 LED, T1 Package D2 1 Open, user-supplied laser J1, J2, J3 3 SMA connectors (edge mount) R15 1 511Ω ±1% resistor (0402) J4 1 1 × 3-pin header (0.1in centers) R17 1 24.9Ω ±1% resistor (0402)* J5, J8, J9 3 Test points R19 1 49.9Ω ±1% resistor (0402) JU7 1 Shunt R27 1 24.9Ω ±1% resistor (0402)** L1, L7 2 Ferrite beads Murata BLM18HG601SN-1 R39 1 1kΩ ±5% resistor (0603) R40 1 10Ω ±5% resistor (0603) C18 R6 1 R7, R14 2 100kΩ variable resistors R8 1 50kΩ variable resistor ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 Evaluates: MAX3996 General Description The MAX3996 evaluation kit (EV kit) is an assembled demonstration board that provides both optical and electrical evaluation of the MAX3996 2.5Gbps laser driver. Evaluates: MAX3996 MAX3996 Evaluation Kit Component List (continued) DESIGNATION QTY TP1-TP6, TP11, TP12 8 DESCRIPTION Test points U1 1 MAX3996CGP (20-QFN) U6 1 MAX4322EUK-T (5-SOT23) None 1 MAX3996 EV kit circuit board, rev B None 1 MAX3996 data sheet *These components are part of the compensation network, which reduces overshoot and ringing. Parasitic series inductance introduces a zero into the laser’s frequency response. R17 and C18 add a pole to cancel this zero. Starting values for most coaxial lasers is R17 = 24.9Ω in series with C18 = 2pF. These values should be experimentally adjusted until the output waveform is optimized. **For electrical evaluation only. Quick Start Electrical Evaluation In the electrical configuration, a test circuit is included to emulate a semiconductor laser with a monitor photodiode. Monitor diode current is provided by Q7, which is controlled by an operational amplifier (U6). The test circuit consisting of U6 and Q7 applies the simulated monitor diode current (the laser bias current divided by a factor of 100) to the MD pin of the MAX3996. To ensure proper operation in the electrical configuration, set up the evaluation board as follows: 1) Ensure that SP9 and SP10 are shorted in order to use the photodiode emulator circuitry. Ensure that SP1 is open. 2) Make sure nothing is installed in the laser socket (Figure 1). 3) Ensure that R27 is installed. 4) Confirm that C18 is open. 5) Set potentiometers R1 and R14 (RSET = R1 + R14) to midscale by turning their screws clockwise at least 30 revolutions or until they faintly click, and then counterclockwise for 15 revolutions. This sets the regulation point for the simulated photodiode current to 1.12V/(5kΩ + 50kΩ) = 20.4µA. The photodiode emulator circuit regulates the DC bias current into Q7 to 100 ✕ 20.4µA ≈ 2mA. until it clicks faintly (30 full revolutions in the 0Ω to 50kΩ range of the multiturn potentiometer). This minimizes the modulation current. 7) Set the potentiometer R7 (RTC) to maximum resistance by turning the screw counterclockwise until it clicks faintly (30 revolutions in the 0Ω to 100kΩ range of the multiturn potentiometer). This minimizes the temperature coefficient (tempco) of the modulation current. 8) Place jumpers across pin 2 (TX_DISABLE) and pin 3 (GND) of J4 (pin 1 is the square pad). This enables the output. 9) Attach a high-speed oscilloscope with 50Ω inputs to J1 (OUT+) through a 50Ω characteristic impedance cable. 10) Apply a differential input signal to J2 (IN+) and J3 (IN-). Set the differential amplitude between 200mVP-P and 2200mVP-P. Note that the differential amplitude is twice the single-ended amplitude. 11) Apply a power-supply voltage of either 3.3V or 5V between J8 (VCC) and J9 (GND). Set the current limit to 300mA. 12) Apply 5V between J5 (5V) and J9 (GND). Set the current limit to 100mA. This provides power to the photodiode feedback emulator. 13) Adjust R8 (RMODSET) until the desired laser modulation current is achieved. IMOD = Signal Amplitude (V) 25Ω Optical Evaluation For optical evaluation of the MAX3996, configure the evaluation kit as follows: 1) Open SP9 and SP10 and short SP1. This disconnects the photodiode emulator circuitry and attaches the bias to the laser. 2) Remove R27. 3) Connect a laser to the board (Figure 1). 4) Set potentiometers R1 and R14 (RSET = R1 + R14) to midscale by turning the screws clockwise at least 30 revolutions or until they click faintly, and then counterclockwise 15 revolutions. This sets the regulation point for the photodiode current to 1.12V/(5kΩ + 50kΩ) = 20.4µA. The resulting laser bias current depends on the relationship between laser power and photodiode output current. 6) Set the potentiometer R8 (RMODSET) to maximum resistance by turning the screw counterclockwise 2 _______________________________________________________________________________________ MAX3996 Evaluation Kit 5) Set the potentiometer R8 (RMODSET) to maximum resistance by turning the screw counterclockwise until it clicks faintly (30 full revolutions in the 0Ω to 50kΩ range of the multiturn potentiometer). This minimizes the modulation current. 6) Set the potentiometer R7 (RTC) to maximum resistance by turning the screw counterclockwise until it clicks faintly (30 revolutions in the 0Ω to 100kΩ range of the multiturn potentiometer). This minimizes the temperature coefficient (tempco) of the modulation current. 7) Attach a 50Ω SMA terminator to J1 (OUT+). This balances the load on the differential outputs of the MAX3966. 8) Place jumpers across pin 2 (TX_DISABLE) and pin 3 (GND) of J4 (pin 1 is the square pad). This enables the output. 9) Apply a differential input signal to J2 (IN+) and J3 (IN-). Set the differential amplitude between 200mVP-P and 2200mVP-P. Note that the differential amplitude is twice the single-ended amplitude. 10) Apply a power-supply voltage of either 3.3V or 5V between J8 (VCC) and J9 (GND). Set the current limit to 300mA. 11) Adjust R1 and R14 (R SET = R1 + R14) until the desired laser bias current is achieved. Turning the R1 and R14 potentiometer screws clockwise increases the laser bias current. 12) Adjust R8 (RMODSET) until the desired modulation current is achieved. Turning the R8 potentiometer screw clockwise increases the laser modulation current. 13) Look at the “eye” output on an oscilloscope. Laser overshoot and ringing can be improved by appropriate selection of R17 and C18, as described in the Design Procedure section of the MAX3996 data sheet. Adjustment and Control Descriptions (see Quick Start first) COMPONENT NAME FUNCTION C21 CPORDLY Removing C21 floats PORDLY pin and minimizes the power-on reset time. Refer to the Design Procedures section of the MAX3996 data sheet. D1 Fault Indicator The LED is illuminated when a fault condition has occurred. The fault condition can be cleared by removing and then reinstalling the jumper at J4. J4 TX_DISABLE R1, R14 RSET The series combination of potentiometers R1 and R14 sets the desired laser DC-current bias point. They set the resistance from MD to ground. Turn the potentiometer screws clockwise to increase average power (decrease the resistance). R7 RTC Potentiometer R7 (RTC), in conjunction with potentiometer R8 (RMODSET), sets the tempco of the laser modulation current. Turn the potentiometer screw clockwise (decrease the resistance) to increase the tempco. R8 RMODSET Potentiometer R8 (RMODSET), in conjunction with potentiometer R7 (RTC), sets the peak-topeak amplitude of the laser modulation current. Turn the potentiometer screw clockwise (decrease the resistance) to increase the modulation amplitude. SP1, SP9, SP10 Open SP1, short SP9, and short SP10 with a solder bridge for electrical evaluation. Short SP1, open SP9, and open SP10 for optical evaluation. Placing a jumper across pin 1 (VCC) and pin 2 (TX_DISABLE) of J4 disables the output (active high). Place a jumper across pin 2 (TX_DISABLE) and pin 3 (GND) of J4 to enable the outputs (pin 1 is the square pad). _______________________________________________________________________________________ 3 Evaluates: MAX3996 WARNING: Consult your laser data sheet to ensure that 20µA of photodiode monitor current does not correspond to excessive laser power. Evaluates: MAX3996 MAX3996 Evaluation Kit 5V LASER SOCKET 4 VCC 1 1: VCC 3 2: LASER CATHODE 3: VCC WITH SHUTDOWN GND 2 4: PHOTODIODE ANODE MAX3996 Figure 1. Optical Connection Diagram 4 _______________________________________________________________________________________ Q3 FMMT491A J1 TP3 FAULT INDICATOR R15 511Ω R4 4.3kΩ VCC2 J9 J8 D1 LED OUT+ GND VCC 5V J4 R7 100kΩ TP11 C16 0.01µF C24 10µF C4 10µF VCC2 RTC R19 49.9Ω L7 L1 RMODSET C26 0.01µF C3 0.01µF 5 4 3 2 1 C7 0.01µF VC C2 C21 0.01µF R8 50kΩ TP12 L3 VCC2 VCC1 VCC TP2 IN+ J3 IN- 9 J2 8 GND OUT+ 17 C10 0.01µF 7 6 IN- MAX3996 U1 OUT- 18 L6 C9 0.01µF IN+ VCC PORDLY TX_DISABLE GND FAULT TC 19 20 C49 0.01µF MODSET VCC2 C15 0.01µF C18 OPEN R17 24.9Ω VCC2 BIAS 10 R2 0Ω MON1 MON2 COMP MD C48 0.01µF 11 12 13 14 15 VCC2 SHDNDRV VCC 16 R16 0Ω C1 0.1µF R5 1kΩ R3 OPEN TP1 SP1 L2 R27 24.9Ω TP4 TP5 BIAS MD C2 0.01µF R1 10kΩ RSET LASER SP10 SP9 R6 1.8kΩ R14 100kΩ TP6 Q7 FMMT591A BIAS PHOTODIODE FEEDBACK EMULATOR U6 Q1 FMMT591A D2 OPEN TP13 VCC1 VCC2 R40 10Ω VCC2 C33 0.01µF PHOTODIODE MAX4322 R39 1kΩ VCC2 MD C44 0.01µF Evaluates: MAX3996 J5 MAX3996 Evaluation Kit Figure 2. MAX3996 EV Kit Schematic _______________________________________________________________________________________ 5 Evaluates: MAX3996 MAX3996 Evaluation Kit Figure 3. MAX3996 EV Kit Component Placement Guide— Component Side 6 Figure 4. MAX3996 EV Kit PC Board Layout—Component Side _______________________________________________________________________________________ MAX3996 Evaluation Kit Evaluates: MAX3996 Figure 5. MAX3996 EV Kit PC Board Layout—Ground Plane Figure 6. MAX3996 EV Kit PC Board Layout—Power Plane Figure 7. MAX3996 EV Kit PC Board Layout—Solder Side Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 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