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| 19-2356; Rev 0; 3/02 MAX3996 Evaluation Kit 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. The output of the electrical evaluation section is interfaced to an SMA connector that can be connected to a 50 terminated oscilloscope. The output of the optical evaluation section is configured for attachment to a laser/monitor diode. o Drives Common-Anode Lasers o Fully Assembled and Tested o LED Fault Indicator o Adjustable Laser Bias Current o Adjustable Laser Modulation Current o Adjustable Laser Modulation Temperature Coefficient o Configured for Electrical Operation; No Laser Necessary Features Evaluates: MAX3996 Component Suppliers SUPPLIER AVX Coilcraft Murata Zetex PHONE 803-946-0690 847-639-6400 814-237-1431 516-543-7100 FAX 803-626-3123 847-639-1469 814-238-0490 516-864-7630 PART MAX3996EVKIT Ordering Information TEMP RANGE 0C to +70C PINPACKAGE 20 QFN TOP MARK -- Component List DESIGNATION C1 C2, C3, C7, C9, C10, C15, C16, C21, C26, C44, C48, C49 C4, C24 C18 C33 D1 D2 J1, J2, J3 J4 J5, J8, J9 JU7 L1, L7 QTY 1 DESCRIPTION 0.1F 10% 10V ceramic capacitor (0402) DESIGNATION L2, L3, L6 Q1, Q7 12 0.01F 10% ceramic capacitors (0402) 10F 10% tantalum capacitors AVX TAJC106K016 Open, user-supplied* 0.01F 10% ceramic capacitor (0603) LED, T1 Package Open, user-supplied laser SMA connectors (edge mount) 1 x 3-pin header (0.1in centers) Test points Shunt Ferrite beads Murata BLM18HG601SN-1 Q3 R1 R2, R16 R3 R4 R5 R6 R7, R14 R8 R15 R17 R19 R27 R39 R40 QTY 3 2 1 1 2 1 1 1 1 2 1 1 1 1 1 1 1 DESCRIPTION Ferrite beads Murata BLM18HG102SN-1 Transistors Zetex FMMT591A NPN Transistor Zetex FMMT491A PNP 10k variable resistor 0 resistors (0402) Open, user-supplied 4.3k 5% resistor (0402) 1k 5% resistor (0402) 1.8k 5% resistor (0402) 100k variable resistors 50k variable resistor 511 1% resistor (0402) 24.9 1% resistor (0402)* 49.9 1% resistor (0402) 24.9 1% resistor (0402)** 1k 5% resistor (0603) 10 5% resistor (0603) 2 1 1 1 1 3 1 3 1 2 ________________________________________________________________ Maxim Integrated Products 1 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. MAX3996 Evaluation Kit Evaluates: MAX3996 Component List (continued) DESIGNATION TP1-TP6, TP11, TP12 U1 U6 None None QTY 8 1 1 1 1 DESCRIPTION Test points MAX3996CGP (20-QFN) MAX4322EUK-T (5-SOT23) MAX3996 EV kit circuit board, rev B MAX3996 data sheet until it clicks faintly (30 full revolutions in the 0 to 50k 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 0 to 100k 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 50 inputs to J1 (OUT+) through a 50 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) 25 *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 = 24.9 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/(5k + 50k) = 20.4A. The photodiode emulator circuit regulates the DC bias current into Q7 to 100 20.4A 2mA. 6) Set the potentiometer R8 (RMODSET) to maximum resistance by turning the screw counterclockwise 2 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/(5k + 50k) = 20.4A. The resulting laser bias current depends on the relationship between laser power and photodiode output current. _______________________________________________________________________________________ MAX3996 Evaluation Kit WARNING: Consult your laser data sheet to ensure that 20A of photodiode monitor current does not correspond to excessive laser power. 5) Set the potentiometer R8 (RMODSET) to maximum resistance by turning the screw counterclockwise until it clicks faintly (30 full revolutions in the 0 to 50k 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 0 to 100k range of the multiturn potentiometer). This minimizes the temperature coefficient (tempco) of the modulation current. 7) Attach a 50 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. Evaluates: MAX3996 Adjustment and Control Descriptions (see Quick Start first) COMPONENT C21 D1 NAME CPORDLY Fault Indicator TX_DISABLE FUNCTION Removing C21 floats PORDLY pin and minimizes the power-on reset time. Refer to the Design Procedures section of the MAX3996 data sheet. 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. 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). 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). 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. 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. Open SP1, short SP9, and short SP10 with a solder bridge for electrical evaluation. Short SP1, open SP9, and open SP10 for optical evaluation. J4 R1, R14 RSET R7 RTC R8 RMODSET SP1, SP9, SP10 _______________________________________________________________________________________ 3 MAX3996 Evaluation Kit Evaluates: MAX3996 5V LASER SOCKET VCC 1 GND 2 4 3 1: VCC 2: LASER CATHODE 3: VCC WITH SHUTDOWN 4: PHOTODIODE ANODE MAX3996 Figure 1. Optical Connection Diagram 4 _______________________________________________________________________________________ VCC1 L1 VCC2 C4 10F R17 24.9 VCC2 L7 C18 OPEN R16 0 TP6 R39 1k VCC2 C15 0.01F VCC2 L6 C16 0.01F U6 TP13 C48 0.01F SP9 MD R19 49.9 VCC2 L3 BIAS SP10 Q7 FMMT591A R40 10 R27 24.9 VCC1 C44 0.01F C24 10F C26 0.01F PHOTODIODE FEEDBACK EMULATOR VCC2 C3 0.01F J5 5V J8 VCC Figure 2. MAX3996 EV Kit Schematic MAX4322 C49 0.01F TP12 TP11 RTC R8 50k 20 TP1 15 TP5 R6 1.8k MODSET OUTOUT+ BIAS 14 VCC 1 TC VCC 19 18 17 16 R7 100k SP1 RMODSET L2 C2 0.01F BIAS Q1 FMMT591A C33 0.01F LASER D2 OPEN VCC2 PHOTODIODE 2 FAULT J9 GND J1 OUT+ D1 LED VCC2 R4 4.3k TP3 Q3 FMMT491A U1 SHDNDRV 13 3 GND MAX3996 MD MD 12 R15 511 4 TX_DISABLE VCC2 5 PORDLY VCC IN+ 7 8 6 VC C2 TP2 C9 0.01F IN+ J2 INC10 0.01F J3 INGND 9 J4 COMP FAULT INDICATOR C21 0.01F MON2 MON1 10 11 C1 0.1F R14 100k RSET R5 1k TP4 R1 10k Evaluates: MAX3996 _______________________________________________________________________________________ C7 0.01F R2 0 R3 OPEN MAX3996 Evaluation Kit 5 MAX3996 Evaluation Kit Evaluates: MAX3996 Figure 3. MAX3996 EV Kit Component Placement Guide-- Component Side Figure 4. MAX3996 EV Kit PC Board Layout--Component Side 6 _______________________________________________________________________________________ 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. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________ 7 (c) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. |
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