a Continuous Wave Laser Average Power Controller ADN2830 FEATURES Bias Current Range 4 mA to 200 mA Monitor Photodiode Current 50 A to 1200 A Closed-Loop Control of Average Power Laser FAIL and Laser DEGRADE Alarms Automatic Laser Shutdown, ALS Full Current Parameter Monitoring 5 V Operation –40C to +85C Temperature Range 5 mm 5 mm 32-Lead LFCSP Package GENERAL DESCRIPTION The ADN2830 provides closed-loop control of the average optical power of a continuous wave (CW) laser diode (LD) after initial factory setup. The control loop adjusts the laser IBIAS to maintain a constant back facet monitor photodiode (MPD) current and thus a constant laser optical power. The external PSET resistor is adjusted during factory setup to set the desired optical power. RPSET is set at 1.23/IAV, where IAV is the MPD current corresponding to the desired optical power. Programmable alarms are provided for laser fail (end of life) and laser degrade (impending fail). APPLICATIONS Fiber Optic Communication To provide monitoring of the MPD current, the MPD can be connected to the IMPD pin. In this case, the MPD current is mirrored to the IMPDMON pin to provide a monitor and internally to the PSET pin to close the control loop. By closing the feedback using IBMON rather than an MPD connected to PSET, the device is configured to control a constant current in the laser rather than a constant optical output power. FUNCTIONAL BLOCK DIAGRAM VCC IBMON IMPDMON ALS FAIL DEGRADE MPD MODE VCC GND VCC LD IMPD GND IBIAS CONTROL PSET ASET RPSET RASET GND GND PAVCAP GND REV. A Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective companies. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 www.analog.com Fax: 781/326-8703 © 2003 Analog Devices, Inc. All rights reserved. V 10%. All specifications T ADN2830–SPECIFICATIONS (VTypical= 5values as specified at 25C.) CC Parameter LASER BIAS (BIAS) Output Current IBIAS Compliance Voltage IBIAS during ALS ALS Response Time MONITOR PD (IMPD) Current Input Voltage POWER SET INPUT (PSET) Capacitance Input Current Voltage Min Typ 4 1.2 Unit 200 mA V µA µs 40 10 50 1.15 ALARM SET (ASET) Allowable Resistance Range Voltage Hysteresis 1.2 1.15 LOGIC INPUTS (ALS, MODE) VIH VIL 2.4 ALARM OUTPUTS (Internal 30 kΩ Pull-Up) VOH VOL 2.4 IBMON IMPDMON IBMON, Division Ratio IMPDMON Division Ratio Compliance Voltage 0 SUPPLY ICC2 VCC 4.5 1.23 1.23 5 1200 1.6 µA V 80 1200 1.35 pF µA V 13 1.35 kΩ V % 0.8 V V 0.4 V V VCC – 1.2 A/A A/A V 5.5 mA V 100 1 25 5.0 to TMAX, unless otherwise noted1. Max VCC 50 MIN Conditions/Comments IBIAS = 0 NOTES 1 Temperature range: –40°C to +85°C. 2 ICC for power calculation is the typical I CC given. Specifications subject to change without notice. –2– REV. A ADN2830 ABSOLUTE MAXIMUM RATINGS 1 (TA = 25°C, unless otherwise noted.) VCC to GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 V Digital Inputs (ALS, Mode) . . . . . . . . . –0.3 V to VCC + 0.3 V Operating Temperature Range Industrial . . . . . . . . . . . . . . . . . . . . . . . . . . –40°C to +85°C Storage Temperature Range . . . . . . . . . . –65°C to +150°C Junction Temperature (TJ Max ) . . . . . . . . . . . . . . . . . 150°C θJA Thermal Impedance2 . . . . . . . . . . . . . . . . . . . . 32°C/W 32-Lead LFCSP Package, Power Dissipation . . . . . . . . . . . . . . (TJ Max – TA)/θJA mW Lead Temperature (Soldering 10 sec) . . . . . . . . . . . . . . 300°C NOTES 1 Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those listed in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. 2 θJA is defined when the part is soldered onto a 4-layer board. ORDERING GUIDE Model Temperature Range Package Description ADN2830ACP32 ADN2830ACP32-REEL7 ADN2830ACP32-REEL –40°C to +85°C –40°C to +85°C –40°C to +85°C 32-Lead LFCSP 32-Lead LFCSP 32-Lead LFCSP CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the ADN2830 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. REV. A –3– WARNING! ESD SENSITIVE DEVICE ADN2830 24 IBMON 23 IBMON 22 GND3 21 VCC3 20 ALS 19 FAIL 18 DEGRADE 17 MODE PIN CONFIGURATION VCC2 25 NC 26 GND2 27 IBIAS 28 GND2 29 GND2 30 IBIAS 31 NC 32 ADN2830 TOP VIEW GND 1 ASET 2 NC 3 PSET 4 IMPD 5 IMPDMON 6 GND4 7 VCC4 8 PIN 1 INDICATOR 16 NC 15 NC 14 GND1 13 NC 12 VCC5 11 VCC1 10 PAVCAP 9 PAVCAP NC = NO CONNECT PIN FUNCTION DESCRIPTIONS Pin No. Mnemonic Function 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 GND ASET NC PSET IMPD IMPDMON GND4 VCC4 PAVCAP PAVCAP VCC1 VCC5 NC GND1 NC NC MODE DEGRADE FAIL ALS VCC3 GND3 IBMON IBMON VCC2 NC GND2 IBIAS GND2 GND2 IBIAS NC Supply Ground Alarm Current Threshold Set Pin No Connect Average Optical Power Set Pin Monitor Photodiode Input Mirrored Current from Monitor Photodiode—Current Source Supply Ground Supply Voltage Average Power Loop Capacitor Average Power Loop Capacitor Supply Voltage Supply Voltage No Connect Supply Ground No Connect No Connect Mode Select: Tied to ALS = Standalone, High = Parallel Current Booster DEGRADE Alarm Output FAIL Alarm Output Automatic Laser Shutdown Supply Voltage Supply Ground Bias Current Monitor Output—Current Source Bias Current Monitor Output—Current Source Supply Voltage No Connect Supply Ground Laser Diode Bias Current Supply Ground Supply Ground Laser Diode Bias Current No Connect –4– REV. A ADN2830 Example: GENERAL Laser diodes have current-in to light-out transfer functions as shown in Figure 1. Two key characteristics of this transfer function are the threshold current, ITH, and slope in the linear region beyond the threshold current, referred to as slope efficiency (LI). IFAIL = 50 mA , N = 1∴ IDEGRADE = 45 mA I ASET = IBIASTRIP 50 mA = = 250 µA 200 N × 200 OPTICAL POWER *RASET = ⌬P PAV ⌬I ITH LI = ⌬P ⌬I 1.23V 1.23 = = 4.92 kΩ I ASET 250 µA The laser degrade alarm, DEGRADE, gives a warning of imminent laser failure if the laser diode degrades further or environmental conditions continue to stress the laser diode, e.g., increasing temperature. The laser fail alarm, FAIL, is activated when: CURRENT • • Figure 1. Laser Transfer Function CONTROL A monitor photodiode (MPD) is required to control the laser diode. The MPD current is fed into the ADN2830 to control the power, continuously adjusting the bias current in response to the laser’s changing threshold current and light to current (LI) slope (slope efficiency). The ADN2830 uses automatic power control (APC) to maintain a constant power over time and temperature. The average power is controlled by the RPSET resistor connected between the PSET pin and ground. The PSET pin is kept 1.23 V above GND. For an initial setup, the RPSET resistor can be calculated using the following formula. 1.23 V RPSET = I AV where IAV is average MPD current. Note the IPSET will change from device to device. It is not required to know exact values for LI and MPD optical coupling. LOOP BANDWIDTH SELECTION Capacitor values greater than 22 nF are used to set the actual loop bandwidth. This capacitor is placed between the PAVCAP pin and ground. It is important that the capacitor is a low leakage multilayer ceramic with an insulation resistance greater than 100 GΩ or a time constant of 1000 sec, whichever is less. The ASET threshold is reached. The ALS pin is set high. This shuts off the modulation and bias currents to the laser diode, resulting in the MPD current dropping to zero. DEGRADE will only be raised when the bias current exceeds 90% of the ASET current. MONITOR CURRENTS IBMON and IMPDMON are current controlled current sources from VCC. They mirror the bias and MPD current for increased monitoring functionality. An external resistor to GND gives a voltage proportional to the current monitored. If the IMPDMON function is not used, the IMPD pin must be grounded and the monitor photodiode must be tied directly to the PSET pin. AUTOMATIC LASER SHUTDOWN When ALS is logic high, the bias current is turned off. Correct operation of ALS can be confirmed by the fail alarm being raised when ALS is asserted. Note that this is the only time DEGRADE will be low while FAIL is high. MODE The MODE feature on the ADN2830 allows the user to operate more than one ADN2830 in parallel current boosting mode to achieve up to N ⫻ 200 mA of bias current (N is the number of ADN2830s in parallel). When using parallel boosting mode, one device is run as the master, the other as the slave. The MODE pin on the master is tied to ALS and the MODE pin on the slave is tied high (see Figure 3 for reference circuit). ALARM INTERFACES ALARMS The ADN2830 has two active high alarms, DEGRADE and FAIL. A resistor between ground and the ASET pin is used to set the current at which these alarms are raised. The current through the ASET resistor is a ratio of (N ⫻ 200):1 to the FAIL alarm threshold (N is the number of ADN2830s in parallel). The DEGRADE alarm will be raised at 90% of this level. The FAIL and DEGRADE outputs have an internal 30 kΩ pull-up resistor that is used to pull the digital high value to VCC. However, the alarm output may be overdriven with an external resistor allowing the alarm interfacing to non-VCC levels. Non-VCC alarm output levels must be below the VCC used for the ADN2830. *The smallest value for R ASET is 1.2 kΩ, as this corresponds to the IBIAS maximum of N ⫻ 200 mA. REV. A –5– ADN2830 POWER CONSUMPTION The ADN2830 die temperature must be kept below 125°C. The exposed paddle should be connected in such a manner that it is at the same potential as the ADN2830 ground pins. Power consumption can be calculated using the following formulas. TDIE = TAMBIENT + θ JA × P ICC = ICCMIN ( P = VCC × ICC + IBIAS × VBIAS _ PIN ) VCC FAIL DEGRADE VCC VCC2 MODE DEGRADE ALS FAIL VCC3 GND3 IBMON LD IBMON 24 16 NC NC NC GND2 GND1 IBIAS NC ADN2830 GND2 VCC5 VCC1 IBIAS PAVCAP 1 VCC VCC4 100nF 8 NC = NO CONNECT 1F PAVCAP GND4 IMPD PSET NC 32 ASET NC IMPDMON GND2 GND MPD 10F GND PLACE 100nF CAP CLOSE TO PIN 8 Figure 2. Test Circuit, Standalone Mode, IMPD Input Not Used –6– REV. A ADN2830 VCC FAIL DEGRADE VCC VCC2 MODE DEGRADE ALS FAIL VCC3 GND3 IBMON IBMON 24 LD MPD 16 NC NC NC GND2 GND1 IBIAS NC ADN2830 GND2 VCC5 VCC1 IBIAS PAVCAP VCC PAVCAP 100nF VCC4 GND4 IMPD PSET NC GND 32 ASET NC IMPDMON GND2 1 100nF 10F GND 8 PLACE 100nF CAP CLOSE TO PIN 8 NC = NO CONNECT VCC2 MODE DEGRADE FAIL ALS VCC3 GND3 IBMON IBMON 24 16 NC NC NC GND1 GND2 IBIAS NC ADN2830 GND2 VCC5 VCC1 IBIAS PAVCAP VCC4 PAVCAP GND4 IMPD PSET NC GND ASET NC 32 IMPDMON GND2 1 8 NC = NO CONNECT Figure 3. Test Circuit, Second ADN2830 Used in Parallel Current Boosting Mode to Achieve 400 mA Max IBIAS REV. A –7– ADN2830 VCC FAIL DEGRADE VCC VCC VCC2 MODE DEGRADE ALS FAIL VCC3 GND3 IBMON IBMON 24 LD MPD 16 NC NC R2 R1 NC GND2 GND1 IBIAS NC ADN2830 GND2 VCC5 VCC1 IBIAS PAVCAP VCC PAVCAP 100nF VCC4 GND4 IMPD PSET NC GND 32 ASET NC IMPDMON GND2 1 10F GND 8 NC = NO CONNECT PLACE 100nF CAP CLOSE TO PIN 8 NOTES 1.FOR DIGITAL CONTROL, REPLACE RPSET WITH A DIGITAL POTENTIOMETER FROM ANALOG DEVICES: ADN2850 10-BIT RESOLUTION, 35 ppm/C TC, EEPROM; AD5242 8-BIT RESOLUTION, 30 ppm/C TC. 2.TOTAL CURRENT TO LASER = IBIAS + IBIAS R1/R2. 3.FOR BEST ACCURACY, SIZE R1 TO HAVE A MAXIMUM VOLTAGE DROP ACROSS IT WITHIN THE HEADROOM CONSTRAINTS. 4.FOR 250 mA EXTRA IBIAS (450 mA TOTAL) FROM AMP1, USE AD8591 AMPLIFIER. AMP1 IS THE OPERATIONAL AMPLIFIER SHOWN IN THIS FIGURE. 5.FOR 350 mA EXTRA IBIAS (550 mA TOTAL) FROM AMP1, USE ANALOG DEVICES’ SSM2211 AMPLIFIER. AMP1 IS THE OPERATIONAL AMPLIFIER SHOWN IN THIS FIGURE. Figure 4. The ADN2830 Configured with Current Multiplier VCC FAIL DEGRADE VCC2 R2 MODE DEGRADE FAIL ALS VCC3 VCC GND3 24 IBMON VCC R1 R2 IBMON CURRENT GAIN = NC R1 NC GND2 GND1 IBIAS VCC NC ADN2830 GND2 VCC5 GND2 VCC1 IBIAS PAVCAP 1 VCC PAVCAP 100nF VCC4 GND4 IMPD PSET GND MPD NC 32 VCC ASET NC IMPDMON AD820 LD 16 NC 8 10F GND PLACE 100nF CAP CLOSE TO PIN 8 NC = NO CONNECT Figure 5. The ADN2830 Configured as Average Power Controller (Bias Current Sourced) –8– REV. A ADN2830 VCC FAIL DEGRADE VCC LD VCC2 MODE DEGRADE ALS FAIL VCC3 GND3 IBMON IBMON 24 16 NC NC NC GND2 GND1 IBIAS NC ADN2830 GND2 VCC5 VCC1 IBIAS PAVCAP VCC PAVCAP 1 100nF VCC4 GND4 IMPD PSET NC GND 32 ASET NC IMPDMON GND2 8 10F GND PLACE 100nF CAP CLOSE TO PIN 8 NC = NO CONNECT Figure 6. The ADN2830 Configured as a Controlled Current Source by Feeding Back the Bias Monitor Current to RPSET REV. A –9– ADN2830 OUTLINE DIMENSIONS 32-Lead Frame Chip Scale Package [LFCSP] (CP-32) Dimensions shown in millimeters 5.00 BSC SQ 0.60 MAX 25 24 PIN 1 INDICATOR 3.25 3.10 SQ 2.95 BOTTOM VIEW 0.50 0.40 0.30 12 MAX 32 1 0.50 BSC 4.75 BSC SQ TOP VIEW 1.00 0.90 0.80 PIN 1 INDICATOR 0.60 MAX 17 16 9 8 0.25 MIN 3.50 REF 0.80 MAX 0.65 NOM 0.05 MAX 0.02 NOM SEATING PLANE 0.30 0.23 0.18 0.20 REF COPLANARITY 0.08 COMPLIANT TO JEDEC STANDARDS MO-220-VHHD-2 Revision History Location Page 6/03—Data Sheet changed from REV. 0 to REV. A. Changes to ABSOLUTE MAXIMUM RATINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Updated OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 –10– REV. A –11– –12– C03020–0–6/03(A)