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precision low power single-supply jfet amplifiers data sheet ad8625 / ad8626 / ad8627 rev. f document feedback 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. specifications subject to change without notice. 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 owners. one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 781.329.4700 ?2003C2013 analog devices, inc. all rights reserved. technical support www.analog.com features sc70 package very low i b : 1 pa max single-supply operation: 5 v to 26 v dual-supply operation: 2.5 v to 13 v rail-to-rail output low supply current: 630 a/amp typ low offset voltage: 500 v max unity gain stable no phase reversal applications photodiode amplifiers ates line-powered/battery-powered instrumentation industrial controls automotive sensors precision filters audio pin configurations 03023-001 2 3 1 4 5 out a v? +in v+ ?in ad8627 5-lead sc70 (ks suffix) nc ?in v+ 2 +in out 3 v? nc 4 nc 1 7 6 5 8 ad8627 nc = no connect 8-lead soic (r-8 suffix) out a ?in a out b 2 +in a ?in b 3 v? +in b 4 v+ 1 7 6 5 8 ad8626 8-lead soic (r-8 suffix) v+ out a out b ?in a ?in b +in a +in b v? ad8626 8-lead msop (rm-suffix) 5 8 4 1 out a out d 11 4 ?in a ?in d 21 3 +in a +in d 31 2 v+ v? 41 1 +in b +in c 51 0 ?in b ?in c 69 out b out c 78 ad8625 14-lead soic (r-suffix) out d out a ?in d ?in a +in d +in a v? v+ +in c +in b ?in c ?in b out c out b ad8625 14-lead tssop (ru-suffix) 8 14 7 1 figure 1. general description the ad862x is a precision jfet input amplifier. it features true single-supply operation, low power consumption, and rail-to-rail output. the outputs remain stable with capacitive loads of over 500 pf; the supply current is less than 630 a/amp. applications for the ad862x include photodiode transimpedance amplification, ate reference level drivers, battery management, both line powered and portable instrumentation, and remote sensor signal conditioning, which includes automotive sensors. the ad862xs ability to swing nearly rail-to-rail at the input and rail-to-rail at the output enables it to be used to buffer cmos dacs, asics, and other wide output swing devices in single-supply systems. the 5 mhz bandwidth and low offset are ideal for precision filters. the ad862x is fully specified over the industrial temperature range. (?40c to +85c). the ad8627 is available in both 5-lead sc70 and 8-lead soic surface-mount packages (sc70 packaged parts are available in tape and reel only). the ad8626 is available in msop and soic packages, while the ad8625 is available in tssop and soic packages.
ad8625/ad8626/ad8627 data sheet rev. f | page 2 of 20 table of contents features .............................................................................................. 1 applications ....................................................................................... 1 pin confi gurations ........................................................................... 1 general description ......................................................................... 1 revision history ............................................................................... 2 specificati ons ..................................................................................... 3 electrical characteristics ............................................................. 3 absolute maximum ratings ............................................................ 5 es d caution .................................................................................. 5 typical performance characteristics ..............................................6 applications information .............................................................. 13 minimizing input current ........................................................ 15 photodiode preamplifier application ...................................... 15 output amplifier for dacs ...................................................... 16 eight - pole sallen key low - pass filter ..................................... 17 outline dimensions ....................................................................... 18 ordering guide .......................................................................... 20 revision history 5/13 rev. e to rev. f changes to applications information section ............................ 13 changes to ordering guide .......................................................... 20 12/10 rev. d to rev. e removed table summary conditions above table 3 ................. 5 updated outline dimensions ....................................................... 18 3/09 rev. c to rev. d updated outline dimensions ....................................................... 18 changes to ordering guide .......................................................... 19 11/04 rev. b to rev. c updated figure codes ....................................................... universal changes to figure 17 and 18 ........................................................... 8 changes to figure 33 and figure 37 ............................................. 11 changes to figure 38 ...................................................................... 12 changes to figure 39 and figure 40 ............................................. 13 changes to figure 41 to figure 44 ................................................ 14 1/04 rev. a to rev. b change to general description ....................................................... 1 change to figure 10 .......................................................................... 7 change to figure13 ........................................................................... 7 change to figure 37 ....................................................................... 11 changes to figure 38 ...................................................................... 12 change to output amplifier for dacs s ection ......................... 15 updated outline dimens ions ....................................................... 19 10/03 rev. 0 to rev. a addition of two new parts ............................................... universal change to general description ....................................................... 1 changes to pin configurations ....................................................... 1 change to specifications t able ........................................................ 3 changes to figure 31 ...................................................................... 10 changes to figure 32 ...................................................................... 11 changes to figure 38 ...................................................................... 12 changes to figure 46 ...................................................................... 16 changes to figure 47 ...................................................................... 16 changes to figure 49 ...................................................................... 17 updated outline dimensions ....................................................... 18 changes to ordering guide .......................................................... 19
data sheet ad8625/ad8626/ ad8627 rev. f | page 3 of 20 specifications electrical character istics @v s = 5 v, v cm = 1.5 v, t a = 25c, unless otherwise noted. table 1 . param eter symbol conditions min typ max unit input characteristics offset voltage v os 0.05 0.5 mv ?40c < t a < +85c 1.2 mv input bias current i b 0.25 1 pa C 40c < t a < +85c 60 pa input offset current i os 0.5 pa C 40c < t a < +85c 25 pa input voltage range 0 3 v common - mode rejection ratio cmrr v cm = 0 v to 2.5 v 66 87 db l arge signal voltage gain a vo r l = 10 k ? , v o = 0.5 v to 4.5 v 100 230 v/mv offset voltage drift ?v os /?t C 40c < t a < +85c 2.5 v/c output characteristics output voltage high v oh 4.92 v i l = 2 ma, C 40c < t a < +85c 4.90 v output vol tage low v ol 0.075 v i l = 2 ma, C 40c < t a < +85c 0.08 v output current i out 10 ma power supply power - supply rejection ratio psrr v s = 5 v to 26 v 80 104 db supply current/amplifier i sy 630 785 a C 40c < t a < +85c 800 a dynamic performance slew rate sr 5 v/s gain bandwidth product gbp 5 mhz phase margin ? m 60 degrees noise performance voltage noise e n p - p 0.1 hz to 10 hz 1.9 v p -p voltage noise density e n f = 1 khz 17.5 nv/hz current noise density i n f = 1 khz 0.4 fa/hz channel separation c s f = 1 khz 104 db
ad8625/ad8626/ad8627 data sheet rev. f | page 4 of 20 @v s = 13 v; v cm = 0 v; t a = 25c, unless otherwise noted. table 2 . parameter symbol conditions min typ max unit input characteri stics offset voltage v os 0.35 0.75 mv C 40c < t a < +85c 1.35 mv input bias current i b 0.25 1 pa C 40c < t a < +85c 60 pa input offset current i os 0.5 pa C 40c < t a < +85c 25 pa input voltage range C 13 +11 v common - mode rejection ratio cmrr v cm = C 13 v to +10 v 76 105 db large signal voltage gain a vo r l = 10 k ?, v o = C 11 v to +11 v 150 310 v/mv offset voltage drift ?v os /?t C 40c < t a < +85c 2.5 v/c output characteristics output voltage high v oh +12.92 v v oh i l = 2 ma, C 40c < t a < +85c +12.91 v output voltage low v ol C 12.92 v v ol i l = 2 ma, C 40c < t a < +85c C 12.91 v output current i out 15 ma power supply power - supply rejection ratio psrr v s = 2.5 v to 13 v 80 104 db supply current/amplifier i sy 710 850 a C 40c < t a < +85c 900 a dynamic performance slew rate sr 5 v/s gain bandwidth product gbp 5 mhz phase margin ? m 60 degrees noise performance voltage noise e n p - p 0.1 hz to 10 hz 2.5 v p -p voltage noise density e n f = 1 khz 16 nv/ hz current noise density i n f = 1 khz 0.5 fa/hz channel separation c s f = 1 khz 105 db
data sheet ad8625/ad8626/ ad8627 rev. f | page 5 of 20 absolute maximum rat ings table 3 . parameter ratings supply voltage 27 v input voltage v s C to v s+ differential input voltage s upply voltage output short - circuit duration indefinite storage temperature range, r package ? 65c to +125c operating temperature range ? 40c to +85c junction temperature range, r package ? 65c to +150c lead temperature range (soldering, 60 sec) 300 c 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 indicated in the operational section of t his specification is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. ja is specified for worst - case conditions when devices are soldered in circuit boards for surface - mount packages. table 4 . package type ja jc unit 5 - lead sc70 (ks) 376 126 c/w 8 - lead msop (rm) 210 45 c/w 8 - lead soic (r) 158 43 c/w 14- lead soic (r) 120 36 c/w 14- lead tssop (ru) 180 35 c/w esd caution
ad8625/ad8626/ad8627 data sheet rev. f | page 6 of 20 typical performance characteristics 03023-002 voltage ( v) 25 20 0 ? 600 ? 400 number of amplifiers ? 200 0 200 400 600 15 10 5 v sy = 12v t a = 25 c figure 2 . input offset voltage offset voltage ( v/ c) 12 0 0 1 2 3 4 5 6 7 8 9 10 03023-003 number of amplifiers 6 4 2 8 10 v sy = 13v figure 3 . offset voltag e drift voltage ( v) 18 16 14 12 10 8 6 4 2 0 ? 400 ? 300 ? 200 ? 100 0 100 200 300 03023-004 number of amplifiers v sy = +3.5v/ ? 1.5v figure 4 . input offset voltage offset voltage ( v/ c) 16 14 12 10 8 6 4 2 0 0 1 2 3 4 5 6 7 8 9 10 03023-005 number of amplifiers v sy = +3.5v/ ? 1.5v figure 5 . offset voltage drift v cm (v) 50 ? 50 ? 40 ? 30 ? 20 ? 10 0 10 20 30 40 ? 15.0 ? 12.5 ? 10.0 ? 7.5 ? 5.0 ? 2.5 0 2.5 5.0 7.5 10.0 12.5 15.0 03023-006 input bias current (pa) v sy = 13v t a = 25 c figure 6 . input bias current vs. v cm v cm (v) ?0.9 0 ?0.1 ?0.2 ?0.3 ?0.4 ?0.5 ?0.6 ?0.7 ?0.8 ? 15.0 ? 12.5 ? 10.0 ? 7.5 ? 5.0 ? 2.5 0 2.5 5.0 7.5 10.0 12.5 15.0 03023-007 input bias current (pa) v sy = 13v t a = 25 c figure 7 . input bias current vs. v cm
data sheet ad8625/ad8626/ ad8627 rev. f | page 7 of 20 temperature ( c) 0.1 100 10 1 ? 50 ? 25 0 25 50 75 100 125 150 03023-008 input bias current (pa) v sy = 13v v cm = 0v figure 8 . input bias current vs. temperature v cm (v) ? 2.0 ? 1.5 ?1.0 ?0.5 0 0.5 1.0 1.5 2.0 ? 5 ? 4 ? 3 ? 2 ? 1 0 1 2 3 4 5 03023-009 input bias current (pa) v sy = +5v or 5v figure 9 . input bias current vs. v cm v cm (v) ? 100 0 100 200 300 400 500 600 700 800 900 1000 ? 15 ? 12 ? 9 ? 6 ? 3 0 3 6 9 12 15 03023-010 input offset voltage ( v) v sy = 13v figure 10 . input offset voltage vs. v cm v cm (v) ? 500 ? 400 ?300 ?200 ?100 0 100 200 300 400 500 ? 1 0 1 2 3 4 03023-011 input offset voltage ( v) v sy = 5v figure 11 . input offset voltage vs. v cm load resistance (k ? ) 10k 100k 1m 10m 0.1 1 10 100 03023-012 open-loop gain (v/v) v sy = +5v v sy = 13v figure 12 . open - loop gain vs. load resistance temperature ( c) 1 10 100 1000 ? 40 25 95 125 03023-013 open-loop gain (v/mv) e c b d a a. v sy = 13v, v o = 11v, r l = 10k ? b. v sy = 13v, v o = 11v, r l = 2k ? c. v sy = +5v, v o = +0.5v/+4.5v, r l = 2k ? d. v sy = +5v, v o = +0.5v/+4.5v, r l = 10k ? e. v sy = +5v, v o = +0.5v/+4.5v, r l = 600 ? figure 13 . open - loop gain vs. temperature
ad8625/ad8626/ad8627 data sheet rev. f | page 8 of 20 output voltage (v) ?400 ?300 ?200 ?100 0 100 200 300 400 500 600 ?15 ?10 ?5 0 5 10 15 03023-014 offset voltage ( v) v sy = 13v r l = 100k ? r l = 10k ? r l = 600 ? figure 14 . input error voltage vs. output vol tage for resistive loads output voltage from supply rails (mv) ?250 ?200 ?150 ?100 ?50 0 50 100 150 200 250 0 50 100 150 200 250 300 03023-015 input voltage ( v) neg rail pos rail v sy = 5v r l = 1k ? r l = 100k ? r l = 10k ? r l = 10k ? r l = 1k ? figure 15 . input error voltage vs. output voltage within 300 mv of supply rails total supply voltage (v) 0 100 200 300 400 500 600 700 800 0 4 8 12 16 20 24 28 03023-016 quiescent current ( a) +125 c +25 c ? 55 c figure 16 . quiescent current vs. supply voltage at different temperatures load current (ma) 1 10 100 1k 10k 0.001 0.01 0.1 1 10 100 03023-017 v sy ? output voltage (mv) v oh v ol v sy = 13v figure 17 . output saturation voltage vs. load current load current (ma) 1 10 100 1k 10k 0.001 0.01 0.1 1 10 100 03023-018 v sy ? output voltage (mv) v sy = 5v v ol v oh figure 18 . output saturation voltage vs. load current frequency (hz) ?30 ?135 ?90 ?45 ?0 45 90 135 180 225 270 315 ?20 ?10 0 10 20 30 40 50 60 70 10k 100k 1m 10m 50m 03023-019 gain (db) phase (degrees) gain phase v sy = 13v r l = 2k ? c l = 40pf figure 19 . open - loop gain and phase margin vs. frequency
data sheet ad8625/ad8626/ ad8627 rev. f | page 9 of 20 frequency (hz) ? 30 ? 135 ? 90 ? 45 ? 0 45 90 135 180 225 270 315 ? 20 ? 10 0 10 20 30 40 50 60 70 10k 100k 1m 10m 50m 03023-020 gain (db) phase (degrees) v sy = 5v r l = 2k ? c l = 40pf gain phase figure 20 . open - loop gain and phase margin vs. frequency frequency (hz) ?30 ?20 ?10 0 10 20 30 40 50 60 70 1k 10k 100k 1m 10m 50m 03023-021 gain (db) g = +100 g = +1 g = +10 v sy = 13v r l = 2k ? c l = 40pf figure 21 . closed - loop gain vs. frequency frequency (hz) ?30 ?20 ?10 0 10 20 30 40 50 60 70 1k 10k 100k 1m 10m 50m 03023-022 gain (db) g = +100 g = +1 g = +10 v sy = 5v r l = 2k ? c l = 40pf figure 22 . closed - loop gain vs. frequency frequency (hz) ?60 ?40 ?20 0 20 40 60 80 100 120 140 1k 10k 100k 1m 10m 03023-023 cmrr (db) v sy = 13v figure 23 . cm rr vs. frequency frequency (hz) ?60 ?40 ?20 0 20 40 60 80 100 120 140 1k 10k 100k 1m 10m 03023-024 cmrr (db) v sy = 5v figure 24 . cmrr vs. frequency frequency (hz) ?60 ?40 ?20 0 20 40 60 80 100 120 140 1k 10k 100k 1m 10m 03023-025 psrr (db) +psrr ?psrr v sy = 13v figure 25 . psrr vs. frequency
ad8625/ad8626/ad8627 data sheet rev. f | page 10 of 20 frequency (hz) ?60 ?40 ?20 0 20 40 60 80 100 120 140 1k 10k 100k 1m 10m 03023-026 psrr (db) +psrr ?psrr v sy = 5v figure 26 . psrr vs. frequency frequency (hz) 0 30 60 90 120 150 180 210 240 270 300 1k 10k 100k 1m 100m 10m 03023-027 z out ( ? ) g = +100 g = +1 g = +10 v sy = 13v figure 27 . output impedance v s. frequency frequency (hz) 0 30 60 90 120 150 180 210 240 270 300 1k 10k 100k 1m 100m 10m 03023-028 z out ( ? ) g = +100 g = +1 g = +10 v sy = 5v figure 28 . output impedance vs. frequency time (400 s/div) 03023-029 voltage (10v/div) input output v sy = 13v figure 29 . no phase reversal settling time ( s) ? 15 ? 10 ? 5 0 5 10 15 0 0.5 1.0 1.5 2.5 2.0 03023-030 output swing (v) ts + (1%) ts + (0.1%) ts ? (1%) ts ? (0.1%) figure 30 . output swing and error vs. settling time capacitance (pf) 0 10 60 50 40 30 20 70 10 100 1k 03023-031 overshoot (%) os? os+ v s = 13v r l = 10k ? v in = 100mv p-p a v = +1 figure 31 . small - signal overshoot vs. load capacitance
data sheet ad8625/ad8626/ ad8627 rev. f | page 11 of 20 capacitance (pf) 0 10 50 40 30 20 70 60 10 100 1k 03023-032 overshoot (%) os? os+ v s = 2.5v r l = 10k ? v in = 100mv p-p a v = +1 figure 32 . small - signal overshoot vs. load capacitance time (1s/div) 03023-033 voltage (50mv/div) v sy = 13v a vo = 100,000v/v 0 figure 33 . 0.1 hz to 10 hz noise time (1s/div) 03023-034 voltage (50mv/div) 0 v sy = 2.5v a vo = 100,000v/v figure 34 . 0.1 hz to 10 hz noise frequency (khz) 0 1 2 3 4 5 6 7 8 9 10 03023-035 voltage (nv) 28 35 42 49 56 21 14 7 0 v sy = 13v 19.7nv/ hz figure 35 . voltage noise density frequency (khz) 0 1 2 3 4 5 6 7 8 9 10 03023-036 voltage (nv) 28 35 42 49 56 21 14 7 0 v sy = 5v 16.7nv/ hz figure 36 . voltage noise density frequency (hz) 10 100 1k 10k 100k 03023-037 thd + noise (db) ?40 ?110 ?100 ?90 ?80 ?70 ?60 ?50 v sy = 5v, v in = 9v p-p v sy = 13v, v in = 18v p-p v sy = 2.5v, v in = 4.5v p-p figure 37 . total harmonic distortion + noise vs. frequency
ad8625/ad8626/ad8627 data sheet rev. f | page 12 of 20 frequency (hz) ? 160 ? 150 ? 140 ? 130 ? 120 ? 110 ? 100 ? 90 ? 80 10 100 1k 10k 100k 03023-049 channel separation (db) v in 2k ? 2k ? 2k ? 20k ? v in = 9v p-p v in = 4.5v p-p v in = 18v p-p figure 38 . channel separation
data sheet ad8625/ad8626/ ad8627 rev. f | page 13 of 20 applications information the ad862x is one of the smallest and most economical jfets offered. it has true single - supply capability and has an input voltage range that extends below the negative rail, allowing the part to accommodate input signals below ground. the rail - to - rail output of the ad862x provides the maximum dynamic range in many applications. to provide a low offset, low noise, high impedance input stage, the ad862x uses n - channel jfets. the input common - mo de voltage extends from 0.2 v below C v s to 2 v below +v s . driving the input of the amplifier, configured in the unity gain buffer, closer than 2 v to the positive rail causes an increase in common - mode voltage error, as illustrated in figure 15 , and a loss of amplifier bandwidth. this loss of bandwidth causes the rounding of the output waveforms shown in figure 39 and figure 40 , which have inputs that are 1 v and 0 v fro m +v s , respectively. the ad862x does not experience phase reversal with input signals close to the positive rail, as shown in figure 29 . for input voltages greater than +v sy , a resistor in series with the ad862xs noninverting input prevents phase reversal at the expense of greater input voltage noise. this current - limiting resistor should also be used if there is a possibility of the input voltage exceeding the positive supply by more than 300 mv, or if an input voltage is appl ied to the ad862x when v sy = 0. either of these conditions damages the amplifier if the condition exists for more than 10 seconds. a 10 k? resistor allows the amplifier to withstand up to 10 v of continuous overvoltage, while increasing the input voltage noise by a negligible amount. time (2 s/div) 03023-038 voltage (2v/div) input output v sy = 5v 4v 4v 0v 0v figure 39 . unity gain follower response to 0 v to 4 v step time (2 s/div) 03023-039 voltage (2v/div) input output v sy = 5v 4v 0v 5v 0v figure 40 . unity gain follower response to 0 v to 5 v step
ad8625/ad8626/ad8627 data sheet rev. f | page 14 of 20 the ad862x can safely withstand input voltages 15 v below v sy if the total voltage between the positive supply and the input terminal is less than 26 v. figu re 41 through figure 43 show the ad862x in different configurations accommodating signals close to the negative rail. the amplifier input stage typically maintains picoamp - level input currents across that input voltage range. time (2 s/div) 03023-040 voltage (1v/div) +5v 20k ? 10k ? 0v ?2.5v v sy = 5v, 0v 5v 0v figure 41 . gain - of - two inverter response to 2.5 v step, centered 1.25 v below ground time (2 s/div) 03023-041 voltage (10mv/div) 5v 60mv 20mv 600 ? 0v v sy = 5v r l = 600 ? 0v figure 42 . unity gain follower response to 40 mv step, centered 40 mv above ground time (2 s/div) 03023-042 voltage (10mv/div) +5v 20k ? 10k ? ?10mv ?30mv 0v v sy = 5v 0v figure 43 . gain - of - two inverter response to 20 mv step, centered 20 mv below ground the ad862x is designed for 16 nv/hz wideband input voltage noise and maintains low noise performance to low frequencies, as shown in figure 35 . this noise performance, along with the ad862xs low input current and current nois e, means that the ad862x contributes negligible noise for applications with large source resistances. the ad862x has a unique bipolar rail - to - rail output stage that swings within 5 mv of the rail when up to 2 ma of current is drawn. at larger loads, the dr op - out voltage increases, as shown in figure 17 and figure 18 . the ad862xs wide bandwidth and fast slew rate allows it to be used with faster signals than older single - supply jfets. figure 44 shows the response of the ad862x, configured in unity gain, to a v in of 20 v p - p at 50 khz. the full - power bandwidth ( fpbw ) of the part is close to 100 khz. time (5 s/div) 03023-043 voltage (5v/div) v sy = 13v r l = 600 ? 0v figure 44 . unity gain follower response to 20 v , 50 khz input signal
data sheet ad8625/ad8626/ ad8627 rev. f | page 15 of 20 minimizing input cur rent the ad862x is guaranteed to 1 pa maximum input current with a 13 v supply voltage at room temperature. careful attention to how the amplifier is used maintains or possibly betters this performance. the amplif iers operating temperature should be kept as low as possible. like other jfet input ampli - fiers, the ad862xs input current doubles for every 10 c rise in junction temperature, as illustrated in figure 8 . on - chip power dissipa tion raises the device operating temperature, causing an increase in input current. reducing supply voltage to cut power dissipation reduces the ad862xs input current. heavy output loads can also increase chip temperature; maintaining a minimum load resis tance of 1 k? is recommended. the ad862x is designed for mounting on pc boards. main - taining picoampere resolution in those environments requires a lot of care. both the board and the amplifiers package have finite resistance. voltage differences between the input pins and other pins, as well as pc board metal traces may cause parasitic currents larger than the ad862xs input current, unless special precautions are taken. to ensure the best result, refer to the adi website for proper board layout seminar materials. two common methods of minimizing parasitic leakages that should be used are guarding of the input lines and maintaining adequate insulation resistance. contaminants, such as solder flux on the boards surface and the amplifiers package, can gre atly reduce the insulation resistance between the input pin and traces with supply or signal voltages. both the package and the board must be kept clean and dry. photodiode preamplif ier application the low input current and offset voltage levels of the ad862x, together with its low voltage noise, make this amplifier an excellent choice for preamplifiers used in sensitive photodiode applications. in a typical photovoltaic preamp circuit, shown in figure 45 , the output of t he amplifier is equal to f p f out (p)r r ) id(r v ? = ? = where: id = photodiode signal current (a). r p = photodiode sensitivity (a/w). r f = value of the feedback resistor, in ? . p = light power incident to photodiode surface, in w. the amplifiers input current, i b , contributes an output voltage error proportional to the value of the feedback resistor. the offset voltage error, v os , causes a small current error due to the photodiodes finite shunt resistance, r d . the resulting output voltage error, v e , is equal to ) (i r v r r v b f os d f e + ? ? ? ? ? ? ? ? + = 1 a shunt resistance on the order of 100 m ? is typical for a small photodiode. resistance r d is a junction resistance that typically drops by a factor of two for every 10 c rise in temperature. in the ad862x, both the offset voltage and drift are low, which helps minimize these errors. with i b val ues of 1 pa and v os of 50 mv, v e for figure 45 is very negligible. also, the circuit in figure 45 results in an snr value of 95 db for a signal bandwidth of 30 khz. 03023-044 r d 100m ? c4 15pf i b i b v os c f 5pf r f 1.5m ? output ad8627 photodiode figure 45 . a photodiode model showing dc error
ad8625/ad8626/ad8627 data sheet rev. f | page 16 of 2 0 output amplifier for dac s many system designers use amplifiers as buffers on the output of amplifiers to increase the dacs output driving capability. the high resolution current output dacs need high precision a mplifiers on their output as current - to - voltage converters (i/v). additionally, many dacs operate with a single supply of 5 v. in a single - supply application, selection of a suitable op amp may be more difficult because the output swing of the amplifier do es not usually include the negative rail, in this case agnd. this can result in some degradation of the dacs specified performance, unless the application does not use codes near zero. the selected op amp needs to have very low offset voltage for a 14 - bit dac, the dac lsb is 300 v with a 5 v reference to eliminate the need for output offset trims. input bias current should also be very low because the bias current multiplied by the dac output impedance (about 10 k ? in some cases) adds to the zero - code err or. rail - to - rail input and output performance is desired. for fast settling, the slew rate of the op amp should not impede the settling time of the dac. output impedance of the dac is constant and code independent, but in order to minimize gain errors, the input impedance of the output amplifier should be as high as possible. the ad862x, with a very high input impedance, i b of 1 pa, and a fast slew rate, is an ideal amplifier for these types of applications. a typical configuration with a popular dac is sh own in figure 46. in these situations, the amplifier adds another time constant to the system, increasin g the settling time of the output. the ad862x, with 5 mhz of bw, helps in achieving a faster effective settling time of the combined dac and amplifier. in applications with full 4 - quadrant multiplying capability or a bipolar output swing, the circuit in figure 47 can be used. in this circuit, the first and second amplifiers provide a total gain of 2, which increases the output voltage span to 20 v. biasing the external amplifier with a 10 v offset from the reference voltage results in a full 4 - quadrant multiplying circuit. 03023-045 ad5551/ad5552 ad8627 dgnd *ad5552 only v dd v reff * v refs * out sclk din cs agnd 5v 2.5v unipolar output ldac* 0.1 f 10 f 0.1 f serial interface 5v figure 46 . unipolar output 03023-046 one channel ad5544 1/2 ad8626 digital interface connections omitted for clarity v ss a gnd f a gnd x v dd v ref x r fb x adr01 vref 10v 1/2 ad8626 ? 13v +13v ? 10v < v out < +10v 10k ? 5k ? 10k ? v out figure 47 . 4 - quadrant m ultiplying application circuit
data sheet ad8625/ad8626/ ad8627 rev. f | page 17 of 20 eight - pole sallen key low - pass filter the ad862xs high input impedance and dc precision make it a great selection for active filters. due to the very low bias current of the ad862x, high value resistors can be used to construct low frequency filters. the ad862xs picoamp - level input currents contribute minimal dc errors. figure 49 shows an example of a 10 hz, 8 - pole sallen key filter constructed using the ad862x. different numbers of the ad862x can be used d epending on the desired response, which is shown in figure 48 . the high value used for r1 minimizes interaction with signal source resistance. pole placement in this version of the filter minimizes the q associated with the lower pole section of the filter. this eliminates any peaking of the noise contribution of resistors in the preceding sections, minimizing the inherent output voltage noise of the filter. 03023-047 v2 v4 v3 v1 frequency (hz) voltage (v) 0.1 0 0.4 0.8 1.2 1 10 100 1k figure 48 . frequen cy response output at different stages of the low - pass filter 03023-048 v in v dd v ee r1 162.3k ? r2 162.3k ? 3 2 11 1 4 u1 r3 25k ? c2 96.19 f d d v3 r10 191.4k ? r5 191.4k ? u2 r4 25k ? c4 69.14 f d r11 286.5k ? r7 286.5k ? u3 r6 25k ? c6 30.86 f d r12 815.8k ? r9 815.8k ? u4 r8 25k ? c8 3.805 f d c1 100 f c3 1/4 ad8625 1/4 ad8625 1/4 ad8625 1/4 ad8625 100 f c5 100 f c7 100 f v1 v2 v3 v4 figure 49 . 10 hz, 8 - pole sallen key low - pass filter
ad8625/ad8626/ad8627 data sheet rev. f | page 18 of 20 outline dimensions c o m p l i a n t t o j e d e c s t a n d a r d s m o - 2 0 3 - a a 1 . 0 0 0 . 9 0 0 . 7 0 0 . 4 6 0 . 3 6 0 . 2 6 2 . 2 0 2 . 0 0 1 . 8 0 2 . 4 0 2 . 1 0 1 . 8 0 1 . 3 5 1 . 2 5 1 . 1 5 0 7 2 8 0 9 - a 0 . 1 0 m a x 1 . 1 0 0 . 8 0 0 . 4 0 0 . 1 0 0 . 2 2 0 . 0 8 3 1 2 4 5 0 . 6 5 b s c c o p l a n a r i t y 0 . 1 0 s e a t i n g p l a n e 0 . 3 0 0 . 1 5 figure 50 . 5 - lead plastic surface - mount package [sc70] (ks - 5) d imensions shown in millimeters c o n t r o l l i n g d i m e n s i o n s a r e i n m i l l i m e t e r s ; i n c h d i m e n s i o n s ( i n p a r e n t h e s e s ) a r e r o u n d e d - o f f m i l l i m e t e r e q u i v a l e n t s f o r r e f e r e n c e o n l y a n d a r e n o t a p p r o p r i a t e f o r u s e i n d e s i g n . c o m p l i a n t t o j e d e c s t andards ms-012-aa 01240 7-a 0.25 (0.0098) 0.17 (0.0067) 1.27 (0.0500) 0.40 (0.0157) 0.50 (0.0196) 0.25 (0.0099) 45 8 0 1.75 (0.0688) 1.35 (0.0532) sea ting plane 0.25 (0.0098) 0.10 (0.0040) 4 1 8 5 5.00 (0.1968) 4.80 (0.1890) 4.00 (0.1574) 3.80 (0.1497) 1.27 (0.0500) bsc 6.20 (0.2441) 5.80 (0.2284) 0.51 (0.0201) 0.31 (0.0122) coplanarity 0.10 figure 51 . 8 - lead standard small outline package [soic_n] narrow body (r - 8) dimensions shown in millimeters and (inches)
data sheet ad8625/ad8626/ ad8627 rev. f | page 19 of 20 c o m p l i a n t t o j e d e c s t a n d a r d s m o - 1 8 7 - a a 6 0 0 . 8 0 0 . 5 5 0 . 4 0 4 8 1 5 0 . 6 5 b s c 0 . 4 0 0 . 2 5 1 . 1 0 m a x 3 . 2 0 3 . 0 0 2 . 8 0 c o p l a n a r i t y 0 . 1 0 0 . 2 3 0 . 0 9 3 . 2 0 3 . 0 0 2 . 8 0 5 . 1 5 4 . 9 0 4 . 6 5 p i n 1 i d e n t i f i e r 1 5 m a x 0 . 9 5 0 . 8 5 0 . 7 5 0 . 1 5 0 . 0 5 1 0 - 0 7 - 2 0 0 9 - b figure 52 . 8 - lead mini small outline package [msop] (rm - 8) dimensions shown in millimeters controlling dimensions are in millimeters; inch dimensions (in p arentheses) are rounded-off millimeter equi v alents for reference on l y and are not appropri a te for use in design. compliant t o jedec s t andards ms-012-ab 060606- a 14 8 7 1 6.20 (0.2441) 5.80 (0.2283) 4.00 (0.1575) 3.80 (0.1496) 8.75 (0.3445) 8.55 (0.3366) 1.27 (0.0500) bsc sea ting plane 0.25 (0.0098) 0.10 (0.0039) 0.51 (0.0201) 0.31 (0.0122) 1.75 (0.0689) 1.35 (0.0531) 0.50 (0.0197) 0.25 (0.0098) 1.27 (0.0500) 0.40 (0.0157) 0.25 (0.0098) 0.17 (0.0067) coplanarit y 0.10 8 0 45 figure 53 . 14 - lead standard small outline package [soic_n] (r - 14) dimensions shown in millimeters and (inches) compliant to jedec standards mo-153-ab-1 061908-a 8 0 4.50 4.40 4.30 14 8 7 1 6.40 bsc pin 1 5.10 5.00 4.90 0.65 bsc 0.15 0.05 0.30 0.19 1.20 max 1.05 1.00 0.80 0.20 0.09 0.75 0.60 0.45 coplanarity 0.10 se a ting plane figure 54 . 14 - lead thin shrink small outli ne package [tssop] (ru - 14) dimensions shown in millimeters
ad8625/ad8626/ad8627 data sheet rev. f | page 20 of 20 ordering guide model 1 , 2 temperature range package description package option branding ad8625aruz C 40c to +85c 14- lead tssop ru -14 ad8625aruz - reel C 40c to +85c 14- lead tssop ru -14 ad8 625arz C 40c to +85c 14- lead soic_n r -14 ad8625arz - reel C 40c to +85c 14- lead soic_n r -14 ad8625arz - reel7 C 40c to +85c 14- lead soic_n r -14 ad8626armz - reel C 40c to +85c 8 - lead msop rm - 8 bja ad8626armz C 40c to +85c 8 - lead msop rm - 8 bja a d8626arz C 40c to +85c 8 - lead soic_n r -8 AD8626ARZ - reel C 40c to +85c 8 - lead soic_n r -8 AD8626ARZ - reel7 C 40c to +85c 8 - lead soic_n r - 8 ad8627aksz - reel C 40c to +85c 5 - lead sc70 ks -5 b9b ad8627aksz - reel7 C 40c to +85c 5 - lead sc70 ks - 5 b9b ad8627aksz - r2 C 40c to +85c 5 - lead sc70 ks - 5 b9b ad8627arz C 40c to +85c 8 - lead soic_n r -8 ad8627arz - reel C 40c to +85c 8 - lead soic_n r -8 ad8627arz - reel7 C 40c to +85c 8 - lead soic_n r -8 1 z = rohs compliant part; # denotes product may be top or bottom marked. 2 for the ad8627aks models, p re - 0542 parts were branded with b9a without #. ? 2003 C 2013 analog devices, inc. all rights reserved. trademarks and registered trademarks are the property of their respective owners. d03023 - 0 - 5/13(f)

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