functional block diagram features bias current range 4ma to 200 ma monitor photo diode current 50ua to 1200ua closed loop control of average power laser fail and laser degrade alarms automatic laser shutdown, als full current parameter monitoring 5 v operation -40'c to 85'c temperature range 5mm x5mm 32 pin lfcsp package applications fiber optic communication 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 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 which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of analog devices. continuous wave laser average power controller 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 photo- diode (mpd) current and hence 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. rev. pre may 2002 adn2830 preliminary technical data preliminary technical data vc c vcc gnd gnd aset ld mpd a l s pavcap gnd v c c g n d pset f a i l i m p d m o n d e g r a d e i b m o n control impd ibias r pset gnd m o d e a
adn2830 specifications parameter min typ max units conditions/comments laser bias (ibias) output current ibias 4 200 ma compliance voltage 1.2 vcc v ibias during als 0.1 ma als response time 10 ? ?2? rev. pre may 2002 notes: 1 temperature range is as follows: -40? to +85? 2 icc for power calculation is the typical icc given. specifications subject to change without notice (v cc = 5v +/-10%. all specifications t min to t max unless otherwise noted 1 . typical values as specified at 25?) preliminary technical data absolute maximum ratings (t a = +25? unless otherwise noted) v cc to gnd................................................................... 7v operating temperature range industrial .................................................-40? to +85? storage temperature range................-65? to +150? junction temperature (t j max)...........................+150? model temperature range package description adn2830acp-32 -40c to +85c 32-lead lfcsp ADN2830ACP-32-RL7 -40c to +85c 32-lead lfcsp ADN2830ACP-32-RL -40c to +85c 32-lead lfcsp
rev. pre may 2002 ?3? adn2830 preliminary technical data pin function description 32 lead lfcsp pin no. pin name function 1 gnd test pin. tie to gnd 2 aset alarm current threshold setting pin 3 nc no connect 4 pset average optical power set pin 5 impd monitor photo diode input 6 impdmon mirrored current from monitor photo diode 7 gnd4 supply ground 8 vcc4 supply voltage 9 pavcap average power loop capacitor. 10 pavcap average power loop capacitor. 11 vcc1 supply voltage 12 vcc5 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=stand-alone, high=parallel current booster. 18 degrade degrade alarm output, open collector 19 fail fail alarm output, open collector 20 als automatic laser shutdown 21 vcc3 supply voltage 22 gnd3 supply ground 23 ibmon bias current monitor output 24 ibmon bias current monitor output 25 vcc2 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. pre may 2002 ?4? adn2830 preliminary technical data general laser diodes have current-in to light-out transfer functions as shown in figure 2. 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. figure 3. laser transfer function control a monitor photo diode, mpd, is required to control the ld. 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. average power is set using the pset pin. potentiometers are connected between these pins and ground. the potentiom- eter, r pset , is used to change the average power. pset is kept 1.23v above gnd. the ratios of current-in-to-current-out are given by the following formulae: r pset = 1.23v ( ) i av where i av is average mpd current. note that i pset will change from device to device. however the control loop will determine actual values. it is not required to know exact values for li or mpd optical cou- pling. loop bandwidth selection capactitor values greater than 22nf 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 an insulation resistance greater than 100g or a time constant of 1000sec, 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 200:1 to the fail alarm threshold. the degrade alarm will be raised at 90% of this level. example: i fail = 50ma s o i degrade = 45ma i aset = ibia strip = 50ma = 250 a 200 200 **r aset = 1.23 v = 1.23 = 4.92 k i aset 250 a the laser degrade alarm, degrade, is provided to give a warning of imminent laser failure if the laser diode degrades further or environmental conditions continue to stress the ld, eg. increasing temperature. the laser fail alarm, fail, is activated when: - the aset threshold is reached. - the als pin is set high. this shuts off the modulation and bias currents to the ld, 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 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. 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 allows the user operate more than one adn2830 in parallel current boosting mode to achieve up to 400ma of bias current. when using the parrallel boosting mode one device is run as the master, the other the slave. the mode pin on the master is tied to als, the mode pin on the slave is tied high (see figure 8 for reference circuit). alarm interfaces a 30k internal pull up resistor is employed to pull the digital high value of the alarm outputs to vcc. however, the adn2830 has a feature which allows the user to externally wire resistors in parallel with the 30k pull-up resistors thus enabling the user to interface to non vcc levels. non vcc alarm output levels must be below the vcc used for the adn2830. **note: the smallest valid value for r aset is 1.2k , as this corresponds to the i bias maximum of 200ma . ibias ith required optical power o p t i c a l p o w e r current current p i li = p i
rev. pre may 2002 ?5? adn2830 preliminary technical data 18 16 32 vcc5 24 nc nc ibias nc gnd2 gnd2 vcc1 gnd1 vcc2 gnd2 nc 100n f gnd vcc 10uf degrad e fail ibi as vcc pa v ca p pavcap i b m o n i b m o n g n d 3 v c c 3 a l s f a i l d e g r a d e m o d e g n d a s e t n c p s e t i m p d i m p d m o n g n d 4 v c c 4 nc vcc ld mpd place 10 0nf cap closetopin8 1uf figure 7. test circuit, stand-alone mode, impd input not used. power consumption the adn2830 die temperature must be kept below 125 o c. the oja is 32 o c/w when soldered in a four layer p.c.b. the lfcsp package has an exposed paddle and as such needs to be soldered to the p.c.b to achieve this thermal performance. tdie = tambient + o j a . p icc = iccmin p = vcc.icc + (ibias.vbias_pin)
rev. pre may 2002 ?6? adn2830 preliminary technical data figure 8. test circuit, second adn2830 used in parallel current boosting mode to achieve 400ma max ibias. 1 8 16 32 24 nc nc ibias nc gnd2 gnd2 vcc1 gnd1 vcc2 gnd2 nc 100nf gnd vc c 10uf degrade fai l ibias vcc pa vcap pavcap i b m o n i b m o n g n d 3 v c c 3 a l s f a i l d e g r a d e m o d e g n d a s e t n c p s e t i m p d i m p d m o n g n d 4 v c c 4 nc vc c ld mpd place 100nf cap closetopin8 1 8 16 32 24 nc nc ibias nc gnd2 gn d2 vcc1 gn d1 vcc2 gnd2 nc ibias pavcap pa vc ap i b m o n i b m o n g n d 3 v c c 3 a l s f a i l d e g r a d e m o d e g n d a s e t n c p s e t i m p d i m p d m o n g n d 4 v c c 4 nc 100nf vcc5 vcc5
rev. pre may 2002 ?7? adn2830 preliminary technical data * for digital control, replace rpset with a digital pot from analog devices. adn2850 10-bit resolution, 50ppm/ ? c tc, eeprom ad5242 8-bit resolution, 50ppm/ ? c tc * total current to laser = ibias + ibias*r1/r2 * for best accuracy, size r1 to have maximum voltage drop across it within the headroom constraints. * for 250ma extra ibias (450ma total) from amp1, use ad8591 amplifier. * for 350ma extra ibias (550ma total) from amp1, use analog devices ssm2211 amplifier. figure 9. the adn2830 configured with current multiplier. 1 8 16 32 vcc5 24 nc nc ibias nc gnd2 gnd2 vcc1 gnd1 vcc2 gnd2 nc 100nf gnd vcc 10uf degrade fail ibias vcc pavcap pavcap i b m o n i b m o n g n d 3 v c c 3 a l s f a i l d e g r a d e m o d e g n d a s e t n c p s e t i m p d i m p d m o n g n d 4 v c c 4 nc vcc ld place 100nf cap closetopin8 + - r1 r2 adn2830 vcc mpd
rev. pre may 2002 ?8? adn2830 preliminary technical data figure 9. the adn2830 configured as average power controller (bias current sourced).. 1 8 16 32 vcc5 24 nc nc ibias nc gnd2 gnd2 vcc1 gnd1 vcc2 gnd2 nc 100nf gnd vcc 10uf degrade fail ibias vcc pavcap pavcap i b m o n i b m o n g n d 3 v c c 3 a l s f a i l d e g r a d e m o d e g n d a s e t n c p s e t i m p d i m p d m o n g n d 4 v c c 4 nc vcc ld place 100nf cap closetopin8 + - r1 r2 adn2830 ad820 vcc vcc mpd vcc current gain = r1 r2
rev. pre may 2002 ?9? adn2830 preliminary technical data outline dimensions dimensions shown in mm. 32-lead (5x5) lfcsp (exposed paddle) exposed paddle should be soldered to the most negative supply of the adn2830 rotated 180 o bottom view 5.00 bsc 4.75 bsc side view 0 . 9 0.5 bsc 0.23 3.45 max 3 . 4 5 m a x 1 top view 5 . 0 b s c 0.40 figure 11. the adn2830 configured as a controlled current source by feeding back the bias monitor current to rpset. 1 8 16 32 vcc5 24 nc nc ibias nc gnd2 gnd2 vcc1 gnd1 vcc2 gnd2 nc 100nf gnd vcc 10uf degrade fail ibias vcc pavcap pavcap i b m o n i b m o n g n d 3 v c c 3 a l s f a i l d e g r a d e m o d e g n d a s e t n c p s e t i m p d i m p d m o n g n d 4 v c c 4 nc vcc ld place 100nf cap closetopin8 adn2830
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