MAX3795EVKIT

19-0031; Rev 0, 11/04 M A X 3 7 9 5 Ev a l u a t i o n K i t The MAX3795 evaluation kit (EV kit) is an assembled demonstration board that provides complete optical and electrical evaluation of the MAX3795 VCSEL driver. The output of the EV kit is interfaced to an SMA connector that can be connected to a 50W terminated oscilloscope. A site for a common cathode VCSEL is provided to allow optical testing. _________________________ Fe a t u r e s Fully Assembled and Tested Single +3.3V Power Supply Operation Allows Optical and Electrical Evaluation _______________Or d e r i n g I n f o r m a t i o n PART TEMP RANGE MAX3795EVKIT -40°C to +85°C IC-PACKAGE 24 Thin QFN ______________________________________________________________ Co m p o n e n t L i s t DESIGNATION C1, C2, C4-C9, C11-C13, C15C17 QTY C3 1 C10 1 C14 1 C18 1 C19, C20 2 D1 1 D2 1 J1-J7 7 JU1-JU7, JU10, JU12-JU13 JU14 None 14 DESCRIPTION 0.01mF –10% ceramic capacitor (0402) 0.047mF –10% ceramic capacitor (0402) OPEN 10mF ceramic capacitor (0805) 10mF –10% tantalum capacitor, case B OPEN* VCSEL laser and photodiode* LED, red T1 package SMA connectors, tab contact, Johnson 142-0701851 11 2-pin header, 0.1in centers 1 12 3-pin header, 0.1in centers Shunts Ferrite Bead, Murata BLM18HD102SN1 (0603) 1.2mH inductor (1008LS) Coilcraft 1008CS-122XKBC NPN transistor (SOT23) Zetex FMMT491A L1-L3 3 L4 1 Q1, Q2 2 DESIGNATION QTY R1, R15 2 R2 1 R14 1 R16 1 DESCRIPTION 50kW variable resistor Bourns 3296W 10kW variable resistor Bourns 3296W 20kW variable resistor Bourns 3296W 500kW variable resistor Bourns 3296W 402W –1% resistor (0402) 2.49kW –1% resistor (0402) 499W –1% resistor (0402 10.0kW –1% resistor (0402) OPEN* 4.75kW –1% resistor (0402) 49.9W –1% resistor (0402) 10W –1% resistor (0402) 1.0kW –1% resistor (0402) 1.0kW –1% resistor (0402) 15kW –1% resistor (0402) 1.69kW –1% resistor (0402) 806W –1% resistor (0402) R3 1 R4 1 R5, R12 2 R6, R13, R28 3 R7, R10 2 R8 1 R9, R11 2 R26 1 R27 1 R34 1 R35 1 R36 1 R51, R53, R56-57 4 TP1-TP3, TP5 TP6-9, TP11-12, 15 Test Point TP13-15, TP2021 U1 1 MAX3795ETG (24 QFN) U2 1 MAX495 (8 SO) *These components are not supplied but can be populated if the user wants to test a VCSEL. __________________________________________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. Ev a l u a t e s : M A X 3 7 9 5 _______________ Ge n e r a l De s c r i p t i o n M A X 3 7 9 5 Ev a l u a t i o n K i t __________________Co m p on e n t Ev a l u a t e s : M A X 3 7 9 5 SUPPLIER Su p p l i e r s PHONE FAX AVX 803-946-0690 803-626-3123 Coilcraft 847-639-6400 847-639-1469 Murata 814-237-1431 814-238-0490 Zetex 516-543-7100 516-864-7630 Note: Please indicate that you are using the MAX3795 when contacting these component suppliers. ________________________Qu i c k St a r t 9) Apply a differential input signal (250mVP-P to 2400mVP-P) between SMA connectors J5 and J7 (IN+ and IN-). 10) Attach a high-speed oscilloscope with a 50W input to the SMA connector J6 (OUT). 11) Connect a +3.3V supply between TP20 (VCC) and TP21 (GND). Set the current limit to about 200mA. Adjust the power supply until the voltage between TP11 and ground is +3.3V. 12) Adjust R1 (RPWRSET) until desired laser bias current is achieved. El e c t r i c a l Ev a l u a t i o n In the electrical configuration, an automatic power control (APC) test circuit is included to emulate a semiconductor laser with a monitor photodiode. Monitor diode current is provided by transistor Q1, which is controlled by an operational amplifier (U2). The APC test circuit, consisting of U2 and Q1, applies the simulated monitor diode current to the MD pin of the MAX3795. To ensure proper operation in the electrical configuration, set up the evaluation board as follows: 1) 2) 3) 5) 6) 7) 8) Adjust R15, the RBIASSET potentiometer, for 2.5kW resistance between TP14 (BIASSET) and ground. Adjust R1, the RPWRSET potentiometer, for 10kW resistance between TP2 (REF) and TP12 (MD). Remove JU12 or Adjust R14, the RPEAKSET potentiometer, for 20kW resistance between TP15 (PEAKSET) and ground, to disable peaking. Adjust R16, the RTC potentiometer, for 0W resistance between TP7 (TC1) and TP8 (TC2), to disable temperature compensation. Adjust R2, the RMODSET potentiometer, for 10kW resistance between TP9 (MODSET) and ground. VJU 5 49.9W 13) The MD and BIAS currents can be monitored at TP1 (VPWRMON) and TP3 (VBIASMON) using the equations below: Place shunts on JU4, JU5, JU6, JU7, JU10, JU13 and JU14 (Refer to Table 1 for details). Remove shunts JU1 and JU2 (Refer to table 1 for detail). To enable the outputs, connect TX_DISABLE to GND by placing a shunt on JU3. Note: When performing the following resistance checks auto ranging DMMS may forward bias the on-chip ESD protection and cause inaccurate measurements. To avoid this manually set the DMM to a high range. 4) IBIAS = IMD = VPWRMON 2 * RPWRSET IBIAS = 9 * VBIASMON 402W Note: If the voltage at TP1 exceeds VPMTH (typical 0.8V) or TP3 exceeds VBMTH (typical 0.8V), the FAULT signal will be asserted and latched. 14) Adjust R2 until the desired laser modulation current is achieved. IMOD = Signal Amplitude ( V ) 50W 15) If peaking is desired, Install JU12. Adjust R14 (RPEAKSET) until the desired amount of peaking is achieved. Op t i c a l Ev a l u a t i o n For optical evaluation of the MAX3795, configure the evaluation kit as follows: 1) 2) Place shunts on JU2, JU6, JU7, JU13 and JU14 (Refer to Table 1 for details). Remove components L2 and C9. Remove the shunts from JU1, JU4 and JU5. 2 _________________________________________________________________________________________ M A X 3 7 9 5 Ev a l u a t i o n K i t 3) 5) Note: When performing the following resistance checks auto ranging DMMS may forward bias the on-chip ESD protection and cause inaccurate measurements. To avoid this manually set the DMM to a high range. 6) 7) 8) 9) 10) 11) 12) 13) Adjust R15, the RBIASSET potentiometer, for 2.5kW resistance between TP14 (BIASSET) and ground. Adjust R1, the RPWRSET potentiometer, for 10kW resistance between TP2 (REF) and TP12 (MD). Open JU12 or adjust R14, the RPEAKSET potentiometer, for 20kW resistance between TP10 (PEAKSET) and ground, to disable peaking. Adjust R16, the RTC potentiometer, for 0W resistance between TP7 (TC1) and TP8 (TC2), to disable temperature compensation. Adjust R2, the RMODSET potentiometer, for 10kW resistance between TP9 (MODSET) and ground. Apply a differential input signal (250mVP-P to 2400mVP-P) between SMA connectors J5 and J7 (IN+ and IN-). Attach the VCSEL fiber connector to an optical/electrical converter. Connect a +3.3V supply between TP20 (VCC) and TP21 (GND). Set the current limit to 200mA. Adjust the power supply until the voltage between TP11 and ground is +3.3V. 14) Adjust R1 (RPWRSET) until desired average optical power is achieved. 15) The MD and BIAS currents can be monitored at TP1 (VPWRMON) and TP3 (VBIASMON) using the equations below: IMD = VPWRMON 2 * RPWRSET IBIAS = 9 * VBIASMON 402W Note: If the voltage at TP1 exceeds VPMTH (typical 0.8V) or TP3 exceeds VBMTH (typical 0.8V), the FAULT signal will be asserted and latched. 16) Adjust R2 (RMODSET) until the desired optical amplitude is achieved. Optical amplitude can be observed on an oscilloscope connected to an optical/electrical converter. VCSEL overshoot and ringing may be improved by appropriate selection of R10 and C10. 16) The falling edge of the optical waveform may improve with peaking. Install JU12 and adjust R14 (RPEAKSET) until the desired amount of peaking is achieved. ___________________________________________Maxim Integrated Products 3 Ev a l u a t e s : M A X 3 7 9 5 4) Install a 0W resistor at R7 to connect the anode of the VCSEL to the output. To enable the outputs, connect TX_DISABLE to GND by placing a shunt on JU3. Connect a common cathode VCSEL as shown in figure 1. Keep leads short to reduce reflection. Ev a l u a t e s : M A X 3 7 9 5 M A X 3 7 9 5 Ev a l u a t i o n K i t Table 1. Adjustment and Control Descriptions (see Quick Start) COMPONENT JU1 JU2 NAME COMP PHOTODIODE JU3 TX_DISABLE JU4 IPD JU5 APC_OPEN JU6 JU7 JU10 FAULT SQUELCH VCCEXT D2 Fault Indicator R1 R2 R14 R15 RPWRSET RMODSET RPEAKSET RBIASSET R16 RTC FUNCTION Enables/disables the APC circuit. Remove shunt to enable APC circuit. Installing a shunt will connect the photodiode of the VCSEL to the MD pin. Used when a VCSEL is installed. Enables/disables the output currents. Install a shunt to enable output currents. Determines the gain of the photodiode emulator. When JU4 is open the gain is 0.02 A/A. When JU4 is shunted the gain is 0.12 A/A. Installing a shunt connects the electrical output of the part to the emulation circuit. Installing a shunt enables the external fault indicator circuit. Installing a shunt enables the squelch function. Installing a shunt provides power to the emulation and fault indicator circuits. LED is illuminated when a fault condition has occurred (Refer to the Detailed Description section of the MAX3740 data sheet). Adjusts transmit optical power to be maintained by the APC loop. Adjusts the laser modulation current. Adjusts the peaking for the falling edge of the VCSEL. In closed-loop configuration it adjusts the maximum bias current available to the APC. In open-loop configuration it adjusts the bias level of the output. Adjusts the temperature compensation of the modulation current. 4 _________________________________________________________________________________________ M A X 3 7 9 5 Ev a l u a t i o n K i t VCC1 L3 BLM18HD102SN1
JU10 VCCEXT VCCEXT TP20 VCC C14 10 F C16 0.01 F C15 0.01 F

C18 10 F
Ev a l u a t e s : M A X 3 7 9 5 TP11 NOISEGEN L4 1 H C17 0.01 F

TP21 GND TP12 JU2 PHOTODIODE R56 800 C12 0.01 F VCCEXT
R1 50k PWRSET C1 0.01 F VCC1 J2 CALOUT+ JU1 COMP R35 15k TP1 PWRMON IN+ 4 IN- VCC VCC1 R13 10k Q2 FMMT491A JU6 FAULT 7 R8 4.7k BIASMON VCC MD COMP OUTEP* SQUELCH C4 0.01 F 8 9 10 11 GND TP7 TC1 R27 1.0k TP8 TC2 VCC1 TP14 BIASSET JU13 C7 0.01 F 16 C20 R15 50k BIASSET
15 14 J6 OUT C8 0.01 F C9 0.1 F

13 C11 0.01 F
R9 49.9 R7 OPEN SB1 SHORT TP9 MODSET C19 OPEN JU14 R26 10 R36 1.69k C10 OPEN R10 OPEN 800 TP5 FAULT R57 800 17 12 R51 R16 500k TC
R12 499 18 OPEN OUT+ FAULT VCCEXT D2 FAULT BIAS U1 MAX3795 TC1 5 JU7 SQUELCH 6 R11 49.9 JU5 APC_OPEN L1 BLM18HD102SN1 VCC
VCC1 R6 10k L2 BLM18HD102SN1 BIASSET TX_DISABLE 3 JU4 IPD R4 2.49k 19 PEAKSET C13 0.01 F 20 MODSET J5 IN+ GND 21 GND 1 2
22 TC2 C5 0.01 F 23 PWRMON 24 JU3 TX_DISABLE 2 4 MAX495 R3 350 3 U2
REF J4 CALOUT- 6 R5 499 TP3 BIASMON C3 0.047 F
J7 IN- Q1 FMMT491A
TP2 REF C2 0.01 F J3 CALIN- 7 C6 0.01 F
J1 CALIN+ R28 10k 2 4 1 3 D1 VCSEL PHOTODIODE R34 1.0k R53 800 JU12 TP15 PEAKSET R14 20k PEAKSET R2 10k MODSET *EP - EXPOSED PAD IS CONNECTED TO GND Figure 1. MAX3795 EV Kit Schematic ___________________________________________Maxim Integrated Products 5 Ev a l u a t e s : M A X 3 7 9 5 M A X 3 7 9 5 Ev a l u a t i o n K i t Figure 2. MAX3795 EV Kit PC Component Placement Guide—Component Side Figure 5. MAX3795 EV Kit PC Board Layout— Power Plane Figure 3. MAX3795 EV Kit PC Board Layout— Component Side Figure 6. MAX3795 EV Kit PC Board Layout— Solder Side Figure 4. MAX3795 EV Kit PC Board Layout— Ground Plane 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___________________6  2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products