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rev. 0 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. a ADN2830 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 ?analog devices, inc., 2002 continuous wave laser functional block diagram gnd gnd pav cap v cc mpd ibmon impdmon als fa i l degrade v cc gnd control gnd impd r pset ibias gnd r aset mode v cc ld pset aset 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 ?0 c to +85 c temperature range 5 mm 5 mm 32-lead lfcsp package applications fiber optic communication 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. r pset is set at 1.23/i av , where i av 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). 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. a verage power controller
rev. 0 e2e ADN2830especifications parameter min typ max unit conditions/comments laser bias (bias) output current ibias 4 200 ma compliance voltage 1.2 v cc v ibias during als 40 () () () ? () ( ? ) = + ( = ) )
rev. 0 ADN2830 e3e absolute maximum ratings 1 (t a = 25 ) + + ( ) ( ) () + + + ()
rev. 0 ADN2830 e4e pin configuration pin 1 indicator top view 16 nc 15 nc 14 gnd1 13 nc v cc 2 25 nc 26 gnd2 27 24 ibmon 12 v cc 5 11 10 pavcap 9 pavcap gnd 1 aset 2 nc 3 pset 4 impd 5 impdmon 6 gnd4 7 v cc 4 8 ibias 28 gnd2 29 gnd2 30 ibias 31 nc 32 23 ibmon 22 gnd3 21 v cc 3 20 als 19 fail 18 degrade 17 mode ADN2830 v cc 1 nc = no connect pin function descriptions pin no. mnemonic function 1g nd supply ground 2 aset alarm current threshold setting pin 3n cn o connect 4 pset average optical power set pin 5 impd monitor photodiode input 6i mpdmon mirrored current from monitor photodiode 7 gnd4 supply ground 8v cc 4 supply voltage 9 pavcap average power loop capacitor 10 pavcap average power loop capacitor 11 v cc 1 supply voltage 12 v cc 5 supply voltage 13 nc no connect 14 gnd1 supply ground 15 nc no connect 16 nc no connect 17 mode mode select: tied to als = standalone, high = parallel current booster 18 degrade degrade alarm output, open collector 19 fail fail alarm output, open collector 20 als automatic laser shutdown 21 v cc 3 supply voltage 22 gnd3 supply ground 23 ibmon bias current monitor output 24 ibmon bias current monitor output 25 v cc 2 supply voltage 26 nc no connect 27 gnd2 supply ground 28 ibias laser diode bias current 29 gnd2 supply ground 30 gnd2 supply ground 31 ibias laser diode bias current 32 nc no connect
rev. 0 ADN2830 ? general laser diodes have current-in to light-out transfer functions as shown in figure 1. two key characteristics of this transfer func- tion are the threshold current, i th , and slope in the linear region beyond the threshold current, referred to as slope efficiency (li). p i li = p i i th current p av optical power 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 th e power, continuously adjusting the bias current in response to the laser? changing threshold current and light to current (li) slope (slope efficiency). the ADN2830 uses automatic power control (apc) to main- tain a constant power over time and temperature. the average power is controlled by the r pset resistor connected between the pset pin and ground. the pset pin is kept 1.23 v above gnd. as a result, the r pset resistor can be calculated using the following formula. r v i pset av = 123 . where i av is average mpd current. note the i pset will change from device to device. it is not re- quired 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 leak- age multilayer ceramic with an insulation resistance greater than 100 g ? or a time constant of 1000 sec, whichever is less. 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. example: imani ma fail degrade === 50 1 45 , i i n ma a aset biastrip = == 200 50 200 250 * r v ia k aset aset == = 123 123 250 492 .. . ? 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 tem- perature. the laser fail alarm, fail, is activated when: ? he aset threshold is reached ? he 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 aset current. monitor currents ibmon and impdmon are current controlled current sources from v cc . they mirror the bias and mpd current for increased monitoring functionality. an external resistor to gnd gives a voltage proportional to the current monitored. 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 this is the only time that 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 the 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, the mode pin on the slave is tied high (see figure 3 for reference circuit). alarm interfaces a 30 k internal pull-up resistor is employed to pull the digital high value of the alarm outputs to v cc . however, the ADN2830 has a feature that allows the user to externally wire resistors, in parallel with the 30 k pull-up resistors thus enabling the user to interface to non-v cc levels. non-v cc alarm output levels must be below the v cc used for the ADN2830. * the smallest value for r aset is 1.2 k ? , as this corresponds to the i bias maximum of n 200 ma.
rev. 0 ADN2830 ? power consumption the ADN2830 die temperature must be kept below 125 c. the j a is 32 c/w when soldered in a four-layer pcb. the lfcsp package has an exposed paddle and as such needs to be soldered to the pcb to achieve this thermal performance. tt p die ambient ja =+ ii cc ccmin = pv i i v cc cc bias bias pin =+ () _ gnd aset nc pset impd impdmon gnd4 v cc 4 nc nc gnd1 nc v cc 5 v cc 1 pav cap pav cap v cc 2 nc gnd2 ibias gnd2 gnd2 ibias nc ibmon ibmon gnd3 v cc 3 als f ail degrade mode 18 16 24 32 nc = no connect mpd ld v cc v cc f ail degrade 1 f 100nf 10 f v cc gnd place 100nf cap close to pin 8 figure 2. test circuit, standalone mode, impd input not used
rev. 0 ADN2830 e7e gnd aset nc pset impd impdmon gnd4 v cc 4 nc nc gnd1 nc v cc 5 v cc 1 pav cap pav cap v cc 2 nc gnd2 ibias gnd2 gnd2 ibias nc ibmon ibmon gnd3 v cc 3 als f ail degrade mode 18 16 24 32 nc = no connect mpd ld v cc v cc f ail degrade 100nf 10 f v cc gnd place 100nf cap close to pin 8 100nf gnd aset nc pset impd impdmon gnd4 v cc 4 nc nc gnd1 nc v cc 5 v cc 1 pav cap pav cap v cc 2 nc gnd2 ibias gnd2 gnd2 ibias nc ibmon ibmon gnd3 v cc 3 als f ail degrade mode 18 16 24 32 nc = no connect figure 3. test circuit, second ADN2830 used in parallel current boosting mode to achieve 400 ma max ibias
rev. 0 ADN2830 e8e gnd aset nc pset impd impdmon gnd4 v cc 4 nc nc gnd1 nc v cc 5 v cc 1 pav cap pav cap v cc 2 nc gnd2 ibias gnd2 gnd2 ibias nc ibmon ibmon gnd3 v cc 3 als f ail degrade mode 18 16 24 32 nc = no connect mpd ld v cc v cc f ail degrade 100nf 10 f v cc gnd place 100nf cap close to pin 8 ADN2830 r1 r2 v cc notes 1.for digital control, replace r pset 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 gnd aset nc pset impd impdmon gnd4 v cc 4 nc nc gnd1 nc v cc 5 v cc 1 pav cap pav cap v cc 2 nc gnd2 ibias gnd2 gnd2 ibias nc ibmon ibmon gnd3 v cc 3 als f ail degrade mode 18 16 24 32 nc = no connect v cc v cc f ail degrade 100nf 10 f v cc gnd place 100nf cap close to pin 8 ADN2830 r1 v cc ad820 mpd v cc ld v cc r2 current gain = r1 r2 figure 5. the ADN2830 configured as average power controller (bias current sourced)
rev. 0 ADN2830 e9e gnd aset nc pset impd impdmon gnd4 v cc 4 nc nc gnd1 nc v cc 5 v cc 1 pav cap pav cap v cc 2 nc gnd2 ibias gnd2 gnd2 ibias nc ibmon ibmon gnd3 v cc 3 als f ail degrade mode 18 16 24 32 nc = no connect v cc f ail degrade 100nf 10 f v cc gnd place 100nf cap close to pin 8 ADN2830 ld v cc figure 6. the ADN2830 configured as a controlled current source by feeding back the bias monitor current to r pset
rev. 0 ADN2830 e10e outline dimensions 32-lead (5 mm 5 mm) lfcsp (exposed paddle) (cp-32) dimensions shown in millimeters compliant to jedec standards mo-220-vhhd-2 0.30 0.23 0.18 12 max 0.25 ref seating plane 0.05 max 0.02 nom coplanarity 0.70 max 0.65 nom 1.00 0.90 0.80 1 32 8 9 25 24 16 17 bottom view 0.50 0.40 0.30 3.50 ref 0.50 bsc pin 1 indicator top view 5.00 bsc sq 4.75 bsc sq sq 2.25 1.70 0.75 pin 1 indicator 0.60 max 0.60 max
e11e
e12e c03020e0e8/02(0) printed in u.s.a.

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