5? features couples ac and dc signals 0.01% servo linearity wide bandwidth, >200 khz high gain stability, 0.005%/c low input-output capacitance low power consumption, < 15mw isolation test voltage, 5300 vac rms , 1 sec. internal insulation distance, >0.4 mm for vde underwriters lab file #e52744 vde app roval #0884 (optional with option 1, add -x001 suf?) il300g replaced by il300-x006 applications power supply feedback voltage/ current medical sensor isolation audio signal interfacing isolate process control transducers digital telephone isolation description the il300 linear optocoupler consists of an algaas irled irradiating an isolated feedback and an output pin photodiode in a bifurcated arrangement. the feed- back photodiode captures a percentage of the led's ?x and generates a control signal (ip 1 ) that can be used to servo the led drive current. this technique com- pensates for the led's non-linear, time, and temperature characteristics. the out- put pin photodiode produces an output signal (ip 2 ) that is linearly related to the servo optical ?x created by the led. the time and temperature stability of the input-output coupler gain (k3) is insured by using matched pin photodiodes that accurately track the output ?x of the led. a typical application circuit (figure 1) uses an operational ampli?r at the circuit input to drive the led. the feedback photodiode sources current to r1 con- nected to the inverting input of u1. the photocurrent, ip1, will be of a magnitude to satisfy the relationship of (ip1=v in /r1). description (continued) the magnitude of this current is directly proportional to the feedback transfer gain (k1) times the led drive current (v in /r1=k1 ?i f ). the op-amp will supply led cur- rent to force suf?ient photocurrent to keep the node voltage (vb) equal to va the output photodiode is connected to a non-inverting voltage follower ampli?r. the photodiode load resistor, r2, performs the current to voltage conversion. the output ampli?r voltage is the product of the output forward gain (k2) times the led current and photodiode load, r2 (v o =i f ?k2 ?r2). therefore, the overall transfer gain (v o /v in ) becomes the ratio of the product of the output forward gain (k2) times the photodiode load resistor (r2) to the product of the feedback transfer gain (k1) times the input resistor (r1). this reduces to v o /v in = (k2 ?r2)/(k1 ?r1). the overall transfer gain is completely independent of the led forward current. the il300 transfer gain (k3) is expressed as the ratio of the ouput gain (k2) to the feedback gain (k1). this shows that the circuit gain becomes the product of the il300 transfer gain times the ratio of the output to input resistors [v o / v in =k3 (r2/r1)]. figure 1. typical application circuit dimensions in inches (mm) 1 2 3 4 8 7 6 5 k2 k1 pin one i.d. . 268 (6.81) . 255 (6.48) 3 4 6 5 .390 (9.91) .379 (9.63) .045 (1.14) .030 (.76) 4 typ. .100 (2.54) typ. 10 typ. 3 ? .305 typ. (7.75) typ. .022 (.56) .018 (.46) .012 (.30) .008 (.20) .135 (3.43 ) .115 (2.92 ) 1 2 8 7 .150 (3.81) .130 (3.30) .040 (1.02) .030 (.76 ) 8 7 6 5 k1 v cc v cc 1 2 3 4 k2 v cc r1 v c r2 il300 vb va + - u1 vin lp 1 v cc - u2 + lp 2 v o ut + i f il300 linear optocoupler
5? il300 il300 terms ki?ervo gain the ratio of the input photodiode current (i p1 ) to the led cur- rent(i f ). i.e., k1 = i p1 / i f . k2?orward gain the ratio of the output photodiode current ( i p2 ) to the led current (i f ), i.e., k2 = i p2 / i f . k3?ransfer gain the transfer gain is the ratio of the forward gain to the servo gain, i.e., k3 = k2/k1. d k3?ransfer gain linearity the percent deviation of the transfer gain, as a function of led or temperature from a speci? transfer gain at a ?ed led current and temperature. photodiode a silicon diode operating as a current source. the output cur- rent is proportional to the incident optical ?x supplied by the led emitter. the diode is operated in the photovoltaic or pho- toconductive mode. in the photovoltaic mode the diode func- tions as a current source in parallel with a forward biased silicon diode. the magnitude of the output current and voltage is depen- dant upon the load resistor and the incident led optical ?x. when operated in the photoconductive mode the diode is connected to a bias supply which reverse biases the silicon diode. the magnitude of the output current is directly propor- tional to the led incident optical ?x. led (light emitting diode) an infrared emitter constructed of algaas that emits at 890 nm operates ef?iently with drive current from 500 m a to 40 ma. best linearity can be obtained at drive currents between 5 ma to 20 ma. its output ?x typically changes by ?.5%/ c over the above operational current range. absolute maximum ratings symbol min. max. unit emitter power dissipation (t a =25 c) p led 160 mw derate linearly from 25 c 2.13 mw/ c forward current lf 60 ma surge current (pulse width <10 m s) lpk 250 ma reverse voltage v r 5v thermal resistance rth 470 c/w junction temperature t j 100 c detector power dissipation p det 50 ma derate linearly from 25 c 0.65 mw/ c reverse voltage v r 50 v junction temperature t j 100 c thermal resistance rth 1500 c/w coupler total package dissipation at 25 c p t 210 mw derate linearly from 25 c 2.8 mw/ c storage temperature t s ?5 150 c operating temperature t op ?5 100 c isolation test voltage 5300 vac rms isolation resistance v io =500 v, t a =25 c v io =500 v, t a =100 c 10 12 10 11 w w
5? il300 characteristics (t a =25 c) symbol min. typ. max. unit test condition led emitter forward voltage v f 1.25 1.50 v i f =10 ma v f temperature coefficient d v f / d c -2.2 mv/ c reverse current i r 110 m av r =5 v junction capacitance c j 15 pf v f =0 v, f=1 mhz dynamic resistance d v f / d i f 6 w i f =10 ma switching time t r t f 1 1 m s m s d i f =2 ma, i fq =10 ma d i f =2 ma, i fq =10 ma detector dark current i d 125nav det =-15 v, i f =0 m a open circuit voltage v d 500 mv i f =10 ma short circuit current i sc 70 m ai f =10 ma junction capacitance c j 12 pf v f =0 v, f=1 mhz noise equivalent power nep 4 x 10 14 w/ ? hz v det =15 v coupled characteristics k1, servo gain (i p1 /i f ) k1 0.0050 0.007 0.011 i f =10 ma, v det =-15 v servo current, see note 1, 2 i p 170 m ai f =10 ma, v det =-15 v k2, forward gain (i p2 /i f ) k2 0.0036 0.007 0.011 i f =10 ma, v det =-15 v forward current i p 270 m ai f =10 ma, v det =-15 v k3, transfer gain (k2/k1) see note 1, 2 k3 0.56 1.00 1.65 k2/k1 i f =10 ma, v det =-15 v transfer gain linearity d k3 0.25 % i f =1 to 10 ma transfer gain linearity d k3 0.5 % i f =1 to 10 ma, t a =0 c to 75 c photoconductive operation frequency response bw (-3 db) 200 khz i fq =10 ma, mod= 4 ma, r l =50 w, phase response at 200 khz -45 deg. v det =-15 v rise time t r 1.75 m s fall time t f 1.75 m s package input-output capacitance c io 1pfv f =0 v, f=1 mhz common mode capacitance c cm 0.5 pf v f =0 v, f=1 mhz common mode rejection ratio cmrr 130 db f=60 hz, r l =2.2 k w notes 1. bin sorting: k3 (transfer gain) is sorted into bins that are 5%, as follows: bin a=0.557?.626 bin b=0.620?.696 bin c=0.690?.773 bin d=0.765?.859 bin e=0.851?.955 bin f=0.945?.061 bin g=1.051?.181 bin h=1.169?.311 bin i=1.297?.456 bin j=1.442?.618 k3=k2/k1. k3 is tested at i f =10 ma, v det =?5 v. 2. bin categories: all il300s are sorted into a k3 bin, indicated by an alpha character that is marked on the part. the bins range from ?? through ?? the il300 is shipped in tubes of 50 each. each tube contains only one category of k3. the category of the parts in the tube is marked on the tube label as well as on each individual part. 3. category options: standard il300 orders will be shipped from the categories that are available at the time of the order. any of the ten categories may be shipped. for customers requiring a narrower selection of bins, four different bin option parts are offered. il300-defg: order this part number to receive categories d,e,f,g only. il300-ef: order this part number to receive categories e, f only. il300-e: order this part number to receive category e only. il300-f: order this part number to receive category f only
5? il300 figure 2. led forward current vs. forward voltage figure 3. led forward current vs. forward voltage figure 4. servo photocurrent vs. led current and temperature figure 5. servo photocurrent vs. led current and temperaturefigure 1.4 1.3 1.2 1.1 1.0 0 5 10 15 20 25 30 35 vf - led forward voltage - v if - led current - ma 1.0 1.1 1.2 1.3 1.4 .1 1 10 100 vf - led forward voltage - v if - led current - ma 100 10 1 .1 0 50 100 150 200 250 300 0 c 25 c 50 c 75 c if - led current - ma ip1- servo photocurrent - a v d =?5 v .1 1 10 100 1 10 100 1000 0 c 25 c 50 c 75 c if - led current - ma ip1- servo photocureent - m a led current and temperature vd = -15v v d =?5 v figure 6. normalized servo photocurrent vs. led current and temperature figure 7. normalized servo photocurrent vs. led current and temperature figure 8. servo gain vs. led current and temperature figure 9. normalized servo gain vs. led current and temperature 25 20 15 10 5 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0 c 25 c 50 c 75 c if - led current - ma normalized photocurrent normalized to:ip1 @ i f =10 ma, t a =25 c, v d =?5 v 100 10 1 .1 .01 .1 1 10 0 c 25 c 50 c 75 c if - led current - ma ip1- normalized photocurrent normalized to ip1 @ i f =10 ma, t a =25 c, v d =?5 v 100 10 1 .1 0.0 0.2 0.4 0.6 0.8 1.0 1.2 if - led current - ma nk1- normalized servo gain 0 25 50 75 85 .1 1 10 100 0.0 0.2 0.4 0.6 0.8 1.0 1.2 if - led current - ma nk1- normalized servo gain 0 25 50 75 100 normalized to: i f =10 ma, t a =25 c
5? il300 figure 10. transfer gain vs. led current and temperature figure 11. normalized transfer gain vs. led current and temperature figure 12. amplitude response vs. frequency figure 13. amplitude and phase response vs. frequency 25 20 15 10 5 0 0.990 0.995 1.000 1.005 1.010 if - led current - ma k3 - transfer gain - (k2/k1) 0 c 25 c 50 c 75 c 0 5 10 15 20 25 0.990 0.995 1.000 1.005 1.010 if - led current - ma k3 - transfer gain - (k2/k1) 0 c 25 c 50 c 75 c normalized to i f =10 ma, t a =25 c 10 6 10 5 10 4 -20 -15 -10 -5 0 5 f - frequency - hz amplitude response - db i f =10 ma, mod= 2 ma (peak) r l =10 k w r l =1 k w 10 7 10 6 10 5 10 4 10 3 -20 -15 -10 -5 0 5 -180 -135 -90 -45 0 45 db phase f - frequency - hz amplitude response - db - phase response - i fq =10 ma mod= 4 ma t a =25 c rl=50 w figure 14. common mode rejection figure 15. photodiode junction capacitance vs. reverse voltage application considerations in applications such as monitoring the output voltage from a line powered switch mode power supply, measuring bioelectric signals, interfacing to industrial transducers, or making ?ating current measurements, a galvanically isolated, dc coupled interface is often essential. the il300 can be used to construct an ampli?r that will meet these needs. the il300 eliminates the problems of gain nonlinearity and drift induced by time and temperature, by monitoring led output ?x. a pin photodiode on the input side is optically coupled to the led and produces a current directly proportional to ?x falling on it . this photocurrent, when coupled to an ampli?r, provides the servo signal that controls the led drive current. the led ?x is also coupled to an output pin photodiode. the output photodiode current can be directly or ampli?d to sat- isfy the needs of succeeding circuits. isolated feedback ampli?r the il300 was designed to be the central element of dc cou- pled isolation ampli?rs. designing the il300 into an ampli?r that provides a feedback control signal for a line powered switch mode power is quite simple, as the following example will illustrate. see figure 17 for the basic structure of the switch mode supply using the siemens tda4918 push-pull switched power supply control chip. line isolation and insulation is provided by the high frequency transformer. the voltage monitor isolation will be provided by the il300. 10 100 1000 10000 100000 1000000 -130 -120 -110 -100 -90 -80 -70 -60 f - frequency - hz cmrr - rejection ratio - db 0 2 4 6 8 10 12 14 02 46810 voltage - v det capacitance - pf
5? il300 figure 16. isolated control ampli?r for best input offset compensation at u1, r2 will equal r3. the value of r1 can easily be calculated from the following. the value of r5 depends upon the il300 transfer gain (k3). k3 is targeted to be a unit gain device, however to minimize the part to part transfer gain variation, siemens offers k3 graded into % bins. r5 can determined using the following equa- tion, or if a unity gain amplifer is being designed (v moni- tor =v out , r1=0), the euation simpli?s to: + - voltag e monito r r1 r2 t o control input iso amp +1 r1 r2 v monitor v a --------------------------- 1 ? ? ?? = 20k w 30k w 5v 3v ------ -1 ? ?? = 5 r5 v out v monitor --------------------------- r3 r1 r2 + () r2k3 ------------------------------------ - = r5 r3 k3 ------- = the isolated ampli?r provides the pwm control signal which is derived from the output supply voltage. figure 16 more closely shows the basic function of the ampli?r. the control ampli?r consists of a voltage divider and a non- inverting unity gain stage. the tda4918 data sheet indicates that an input to the control ampli?r is a high quality operational ampli?r that typically requires a +3v signal. given this infor- mation, the ampli?r circuit topology shown in figure 18 is selected. the power supply voltage is scaled by r1 and r2 so that there is +3 v at the non-inverting input (va) of u1. this voltage is offset by the voltage developed by photocurrent ?wing through r3. this photocurrent is developed by the optical ?x created by current ?wing through the led. thus as the scaled monitor voltage (va) varies it will cause a change in the led current necessary to satisfy the differential voltage needed across r3 at the inverting input. the ?st step in the design procedure is to select the value of r3 given the led quiescent current (i fq ) and the servo gain (k1). for this design, i fq =12 ma. figure 4 shows the servo pho- tocurrent at i fq is found to be 100 m a. with this data r3 can be calculated. r3 v b i pl ------ 3v 100 m a ----------------- - = = 30k w = figure 17. switch mode power supply figure 18. dc coupled power supply feedback ampli?r switch xformer switch mode r egulato r tda4918 isolated f eedbac k control 110/ 2 20 m ai n dc output ac/dc r ectifie r ac/dc r ectifie r 8 7 6 5 100 pf 4 3 1 2 8 6 7 k1 v cc v cc 1 2 3 4 k2 v cc v monitor r1 20 k w r2 30 k w r3 30 k w r4 100 w v out to contro l input r5 30 k w il300 vb va + - u1 lm201
5? il300 table 1 gives the value of r5 given the production k3 bins . table 1. r5 selection the last step in the design is selecting the led current limiting resistor (r4). the output of the operational ampli?r is targeted to be 50% of the vcc, or 2.5 v. with an led quiescent current of 12 ma the typical led (v f ) is 1.3 v. given this and the opera- tional output voltage, r4 can be calculated. . the circuit was constructed with an lm201 differential opera- tional ampli?r using the resistors selected. the ampli?r was compensated with a 100 pf capacitor connected between pins 1 and 8. the dc transfer charateristics are shown in figure 19. the ampli?r was designed to have a gain of 0.6 and was mea- sured to be 0.6036. greater accurracy can be achieved by adding a balancing circuit, and potentiometer in the input divider, or at r5. the circuit shows exceptionally good gain lin- earity with an rms error of only 0.0133% over the input voltage range of 4 v? v in a servo mode; see figure 20. figure 19. transfer gain bins min. max. k3 typ. r5 resistor k w 1% k w a 0.560 0.623 0.59 50.85 51.1 b 0.623 0.693 0.66 45.45 45.3 c 0.693 0.769 0.73 41.1 41.2 d 0.769 0.855 0.81 37.04 37.4 e 0.855 0.950 0.93 32.26 32.4 f 0.950 1.056 1.00 30.00 30.0 g 1.056 1.175 1.11 27.03 27.0 h 1.175 1.304 1.24 24.19 24.0 i 1.304 1.449 1.37 21.90 22.0 j 1.449 1.610 1.53 19.61 19.4 r4 v opamp v f i fq -------------------------------- 2.5v 1.3v 12ma ------------------------------ 1 0 0 w = = = 6.0 5.5 5.0 4.5 4.0 2.25 2.50 2.75 3.00 3.25 3.50 3.75 vin - input voltage - v vout - ooutput voltage - v vout = 14.4 mv + 0.6036 x vin lm 201 ta = 25 c figure 20. linearity error vs. input voltage the ac characteristics are also quite impressive offering a -3 db bandwidth of 100 khz, with a -45 phase shift at 80 khz as shown in figure 21. figure 21. amplitude and phase power supply control the same procedure can be used to design isolation ampli?rs that accept biploar signals referenced to ground. these ampli? ers circuit con?urations are shown in figure 22. in order for the ampli?r to respond to a signal that swings above and below ground, the led must be prebiased from a separate source by using a voltage reference source (vref1). in these designs, r3 can be determined by the following equation. 6.0 5.5 5.0 4.5 4.0 -0.015 -0.010 -0.005 0.000 0.005 0.010 0.015 0.020 0.025 vin - input voltage - v linearity error - % lm201 10 3 10 4 10 5 10 6 -8 -6 -4 -2 0 2 -180 -135 -90 -45 0 45 db phase f - frequency - hz amplitude rresponse - db phase response - r3 v ref1 i p1 ------------ - v ref1 k1i fq --------------- = =
5? il300 these ampli?rs provide either an inverting or non-inverting transfer gain based upon the type of input and output ampli?r. table 2 shows the various con?urations along with the spe- ci? transfer gain equations. the offset column refers to the calculation of the output offset or vref2 necessary to provide a zero voltage output for a zero voltage input. the non-inverting input ampli?r requires the use of a bipolar supply, while the inverting input stage can be implemented with single supply operational ampli?rs that permit operation close to ground. for best results, place a buffer transistor between the led and output of the operational ampli?r when a cmos opamp is used or the led i fq drive is targeted to operate beyond 15 ma. finally the bandwidth is in?enced by the magnitude of the closed loop gain of the input and output ampli?rs. best band- widths result when the ampli?r gain is designed for unity. figure 22. non-inverting and inverting ampli?rs table 2. optolinear ampli?rs amp[i?r input output gain offset non-inverting inverting inverting non-inverting non-inverting inverting inverting non-inverting non-inverting inverting vcc 20pf 4 1 2 3 4 8 7 6 5 +vref2 r5 r6 7 2 4 3 vo r4 r3 ?ref1 vin r1 r2 3 7 6 + +vcc 100 w 6 il 300 2 vcc vcc vcc vcc + vcc vcc 20pf 4 1 2 3 4 8 7 6 5 +vref2 7 2 4 3 vout r4 r3 +vref1 vin r1 r2 3 7 6 + +vcc 100 w 6 2 vcc vcc vcc + vcc non-inverting input non-inverting output inverting input inverting output il 300 vcc v out k3 r4 r2 v in r3 (r1+r2) = v ref1 r4 k3 r3 v ref2 = v out k3 r4 r2 (r5+r6) v in r3 r5 (r1 +r2) = ? ref1 r4 (r5+r6) k3 r3 r6 v ref2 = v out ?3 r4 r2 (r5+r6) v in r3 r5 (r1 +r2) = v ref1 r4 (r5+r6) k3 r3 r6 v ref2 = v out ?3 r4 r2 v in r3 (r1 +r2) = ? ref1 r4 k3 r3 v ref2 =
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