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general description the MAX9945 operational amplifier features an excellent combination of low operating power and low input volt- age noise. in addition, mos inputs enable the MAX9945 to feature low input bias currents and low input current noise. the device accepts a wide supply voltage range from 4.75v to 38v and draws a low 400? quiescent cur- rent. the MAX9945 is unity-gain stable and is capable of rail-to-rail output voltage swing. the MAX9945 is ideal for portable medical and industri- al applications that require low noise analog front-ends for performance applications such as photodiode trans- impedance and chemical sensor interface circuits. the MAX9945 is available in both an 8-pin ?ax and a space-saving, 6-pin tdfn package, and is specified over the automotive operating temperature range (-40? to +125?). applications medical pulse oximetry photodiode sensor interface industrial sensors and instrumentation chemical sensor interface high-performance audio line out active filters and signal processing features ? +4.75v to +38v single-supply voltage range ? ?.4v to ?9v dual-supply voltage range ? rail-to-rail output voltage swing ? 400? low quiescent current ? 50fa low input bias current ? 1fa/ hz low input current noise ? 15nv/ hz low noise ? 3mhz unity-gain bandwidth ? wide temperature range from -40? to +125? ? available in space-saving, 6-pin tdfn package (3mm x 3mm) MAX9945 38v, low-noise, mos-input, low-power op amp ________________________________________________________________ maxim integrated products 1 19-4398; rev 0; 2/09 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. ordering information part temp range pin- package top mark MAX9945att+ -40? to +125? 6 tdfn-ep* aue MAX9945aua+ -40? to +125? 8 ?ax + denotes a lead(pb)-free/rohs-compliant package. * ep = exposed pad. ?ax is a registered trademark of maxim integrated products, inc. in- in+ out v ee v cc photodiode signal conditioning/ filters adc MAX9945 typical operating circuit
MAX9945 38v, low-noise, mos-input, low-power op amp 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v cc = +15v, v ee = -15v, v in+ = v in- = gnd = 0, r out = 100k to gnd, t a = -40? to +125?, typical values are at t a = +25?, unless otherwise noted.) (note 2) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. supply voltage (v cc to v ee ) ..................................-0.3v to +40v in+, in-, out voltage......................(v ee - 0.3v) to (v cc + 0.3v) in+ to in- .............................................................................?2v out short circuit to ground duration....................................10s continuous input current into any pin .............................?0ma continuous power dissipation (t a = +70?) 6-pin tdfn-ep (derate 23.8mw/? above +70?) multilayer board ....................................................1904.8mw package thermal resistance (note 1) ja ..............................................................................42?/w jc ................................................................................9?/w 8-pin ?ax (derate 4.8mw/? above +70?) multilayer board ......................................................387.8mw package thermal resistance (note 1) ja .........................................................................206.3?/w jc ..............................................................................42?/w operating temperature range .........................-40? to +125? junction temperature ......................................................+150? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) .................................+300? parameter symbol conditions min typ max units dc electrical characteristics t a = +25? v ee v cc - 1.2 input voltage range v in+ , v in- guaranteed by cmrr t a = t min to t max v ee v cc - 1.4 v t a = +25? ?.6 ? input offset voltage v os t a = t min to t max ? mv input offset voltage drift v os - t c 2 ?/? input bias current (note 3) i b 50 fa v cm = v ee to v cc - 1.2v, t a = +25? 78 94 common-mode rejection ratio cmrr v cm = v ee to v cc - 1.4v, t a = t min to t max 78 94 db v ee + 0.3v v out v cc - 0.3v, r out = 100k to gnd 110 130 open-loop gain a ol v ee + 0.75v v out v cc - 0.75v, r out = 10k to gnd 110 130 db output short-circuit current i sc 25 ma note 1: package thermal resistances were obtained using the method described in jedec specification jesd51-7, using a four- layer board. for detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial .
MAX9945 38v, low-noise, mos-input, low-power op amp _______________________________________________________________________________________ 3 parameter symbol conditions min typ max units r out = 10k to gnd t a = t min to t max v ee + 0.26 v ee + 0.45 output voltage low v ol r out = 100k to gnd t a = t min to t max v ee + 0.05 v ee + 0.15 v r out = 10k to gnd t a = t min to t max v cc - 0.45 v cc - 0.24 output voltage high v oh r out = 100k to gnd t a = t min to t max v cc - 0.15 v cc - 0.03 v ac electrical characteristics input current-noise density i n f = 1khz 1 fa/ hz input voltage noise v np-p f = 0.1hz to 10hz 2 v p-p f = 100hz 25 f = 1khz 16.5 input voltage-noise density v n f = 10khz 15 nv/ hz gain bandwidth gbw 3 mhz slew rate sr 2.2 v/? capacitive loading (note 4) c load no sustained oscillations 120 pf total harmonic distortion thd v out = 4.5v p-p , a v = 1v/v, f = 10khz, r out = 10k to gnd 97 db power-supply electrical characteristics power-supply voltage range v cc - v ee guaranteed by psrr, v ee = 0 +4.75 +38 v power-supply rejection ratio psrr v cc - v ee = +4.75v to +38v 82 100 db t a = +25? 400 700 quiescent supply current i cc t a = t min to t max 850 ? electrical characteristics (continued) (v cc = +15v, v ee = -15v, v in+ = v in- = gnd = 0, r out = 100k to gnd, t a = -40? to +125?, typical values are at t a = +25?, unless otherwise noted.) (note 2) note 2: all devices are 100% production tested at t a = +25?. all temperature limits are guaranteed by design. note 3: in+ and in- are internally connected to the gates of cmos transistors. cmos gate leakage is so small that it is impractical to test in production. devices are screened during production testing to eliminate defective units. note 4: specified over all temperatures and process variation by circuit simulation.
MAX9945 38v, low-noise, mos-input, low-power op amp 4 _______________________________________________________________________________________ typical operating characteristics (v cc = +15v, v ee = -15v, v in+ = v in- = gnd = 0, r out = 100k to gnd, t a = -40? to +125?, typical values are at t a = +25?, unless otherwise noted.) quiescent supply current vs. supply voltage and temperature MAX9945 toc01 supply voltage (v) supply current ( a) 35 30 25 20 15 10 300 400 500 600 200 5 t a = +125 c t a = +25 c t a = -40 c output voltage swing low vs. temperature MAX9945 toc02 temperature ( c) v ol - v ee (v) 100 120 80 60 40 20 0 -20 0.10 0.05 0.15 0.20 0.25 0 -40 i sink = 1.0ma i sink = 0.1ma output voltage swing high vs. temperature MAX9945 toc03 temperature ( c) v cc - v oh (v) 100 120 80 60 40 20 0 -20 0.10 0.05 0.15 0.20 0.25 0 -40 i source = 1.0ma i source = 0.1ma input bias current vs. temperature MAX9945 toc04 temperature ( c) i bias (pa) 100 80 60 02040 -20 0 10 20 30 40 50 60 70 80 -10 -40 120 input voltage 0.1hz to 10hz noise MAX9945 toc05 1s/div 1 v/div input voltage-noise density vs. frequency MAX9945 toc06 frequency (hz) input voltage-noise density (nv/ hz) 10,000 100,000 1000 100 10 100 1000 10 1 total harmonic distortion vs. frequency MAX9945 toc07 frequency (hz) thd (db) 100,000 10,000 1000 -90 -70 -80 -110 -100 100 v cc - v ee = 30v, 4.5v p-p , r l = 10k total harmonic distortion + noise vs. frequency MAX9945 toc08 frequency (hz) thd+n (db) -90 -80 -70 -60 -50 -100 100,000 10,000 100 1000 10 v cc - v ee = 30v 4.5v p-p r l = 10k
input offset voltage vs. common-mode voltage MAX9945 toc09 common-mode voltage (v) input offset voltage ( v) 10 5 0 -10 -5 1000 800 0 600 400 200 -15 MAX9945 38v, low-noise, mos-input, low-power op amp _______________________________________________________________________________________ 5 input offset voltage vs. temperature MAX9945 toc10 temperature ( c) input offset voltage ( v) 100 120 80 40 60 -20 0 20 1000 800 0 600 400 200 -40 v cm = 0 v cm = v ee v cm = v cc - 1.2v open-loop gain vs. frequency MAX9945 toc11 frequency (hz) open-loop gain (db) 120 80 -40 40 0 1m 1 10 100 1k 10k 100k 1m 10m common-mode rejection ratio vs. frequency MAX9945 toc12 frequency (hz) cmrr (db) 1m 100k 100 1k 10k -90 -80 -70 -60 -50 -40 -30 -20 -100 10 10m power-supply rejection ratio vs. frequency MAX9945 toc13 frequency (hz) psrr (db) 1m 100k 10k 1k 100 10 -100 -80 -60 -40 -20 0 -120 1 10m unipolar psrr- unipolar psrr+ bipolar psrr resistor isolation vs. capacitive load MAX9945 toc14 r iso ( ) c load (pf) 100 10 1000 10,000 100 1 stable unstable typical operating characteristics (continued) (v cc = +15v, v ee = -15v, v in+ = v in- = gnd = 0, r out = 100k to gnd, t a = -40? to +125?, typical values are at t a = +25?, unless otherwise noted.)
MAX9945 38v, low-noise, mos-input, low-power op amp 6 _______________________________________________________________________________________ typical operating characteristics (continued) (v cc = +15v, v ee = -15v, v in+ = v in- = gnd = 0, r out = 100k to gnd, t a = -40? to +125?, typical values are at t a = +25?, unless otherwise noted.) large signal-step response MAX9945 toc19 1 c l = 100pf small signal-step response MAX9945 toc20 2 large-signal response vs. frequency MAX9945 toc17 frequency (khz) output voltage (v p-p ) 10,000 1000 100 10 5 10 15 25 20 30 0 1 r load = 100k large signal-step response MAX9945 toc18 4 c l = 100pf output impedance vs. frequency MAX9945 toc16 frequency (hz) output impedance ( ) 1m 100k 10k 1k 100 0.10 1.00 10.00 100.00 1000.00 0.01 10 10m acl = 10 acl = 1 op-amp stability vs. capacitive and resistive loads MAX9945 toc15 parallel load resistance (k ) parallel load capacitance (pf) 10,000 100 1000 1000 100 10,000 10 10 stable unstable
detailed description the MAX9945 features a combination of low input cur- rent and voltage noise, rail-to-rail output voltage swing, wide supply voltage range, and low-power operation. the mos inputs on the MAX9945 make it ideal for use as transimpedance amplifiers and high-impedance sensor interface front-ends in medical and industrial applications. the MAX9945 can interface with small signals from either current-sources or high-output impedance voltage sources. applications include pho- todiode pulse oximeters, ph sensors, capacitive pres- sure sensors, chemical analysis equipment, smoke detectors, and humidity sensors. a high 130db open-loop gain (typ) and a wide supply voltage range, allow high signal-gain implementations prior to signal conditioning circuitry. low quiescent supply current makes the MAX9945 compatible with portable systems and applications that operate under tight power budgets. the combination of excellent thd, low voltage noise, and mos inputs also make the MAX9945 ideal for use in high-performance active fil- ters for data acquisition systems and audio equipment. low-current, low-noise input stage the MAX9945 features a mos-input stage with only 50fa (typ) of input bias current and a low 1fa/ hz (typ) input current-noise density. the low-frequency input voltage noise is a low 2? p-p (typ). the input stage accepts a wide common-mode range, extending from the negative supply, v ee, to within 1.2v of the positive supply, v cc . rail-to-rail output stage the MAX9945 output stage swings to within 50mv (typ) of either power-supply rail with a 100k load and pro- vides a 3mhz gbw with a 2.2v/? slew rate. the device is unity-gain stable, and unlike other devices with a low quiescent current, can drive a 120pf capaci- tive load without compromising stability. applications information high-impedance sensor front ends high-impedance sensors can output signals of interest in either current or voltage form. the MAX9945 inter- faces to both current-output sensors such as photo- diodes and potentiostat sensors, and high-impedance voltage sources such as ph sensors. for current-output sensors, a transimpedance amplifier is the most noise-efficient method for converting the input signal to a voltage. high-value feedback resistors are commonly chosen to create large gains, while feed- back capacitors help stabilize the amplifier by cancel- ing any zeros in the transfer function created by a highly capacitive sensor or cabling. a combination of low-current noise and low-voltage noise is important for these applications. take care to calibrate out photodi- ode dark current if dc accuracy is important. the high bandwidth and slew rate also allows ac signal pro- cessing in certain medical photodiode sensor applica- tions such as pulse oximetry. MAX9945 38v, low-noise, mos-input, low-power op amp _______________________________________________________________________________________ 7 pin description pin tdfn-ep ?ax name function 1 6 out amplifier output 24v ee negative power supply. bypass v ee with 0.1? ceramic and 4.7? electrolytic capacitors to quiet ground plane if different from v ee. 3 3 in+ noninverting amplifier input 4 2 in- inverting amplifier input 5 1, 5, 8 n.c. no connection. not internally connected. 67v cc positive power supply. bypass v cc with 0.1? ceramic and 4.7? electrolytic capacitors to quiet ground plane or v ee . ep exposed pad. connect to v ee externally. connect to a large copper plane to maximize thermal performance. not intended as an electrical connection (tdfn only).
MAX9945 for voltage-output sensors, a noninverting amplifier is typically used to buffer and/or apply a small gain to, the input voltage signal. due to the extremely high imped- ance of the sensor output, a low input bias current with a small temperature variation is very important for these applications. power-supply decoupling the MAX9945 operates from a +4.75v to +38v, v ee ref- erenced power supply. bypass the power-supply inputs v cc and v ee to a quiet copper ground plane, with a 0.1? ceramic capacitor in parallel with a 4.7? electrolytic capacitor, placed close to the leads. layout techniques a good layout is critical to obtaining high performance especially when interfacing with high-impedance sen- sors. use shielding techniques to guard against para- sitic leakage paths. for transimpedance applications, for example, surround the inverting input, and the traces connecting to it, with a buffered version of its own voltage. a convenient source of this voltage is the noninverting input pin. pins 1, 5, and 8 on the ?ax package are unconnected, and can be connected to an analog common potential, or to the driven guard potential, to reduce leakage on the inverting input. a good layout guard rail isolates sensitive nodes, such as the inverting input of the MAX9945 and the traces connecting to it (see figure 1), from varying or large volt- age differentials that otherwise occur in the rest of the circuit board. this reduces leakage and noise effects, allowing sensitive measurements to be made accurately. take care to also decrease the amount of stray capaci- tance at the op amp? inputs to improve stability. to achieve this, minimize trace lengths and resistor leads by placing external components as close as possible to the package. if the sensor is inherently capacitive, or is connected to the amplifier through a long cable, use a low-value feedback capacitor to control high-frequency gain and peaking to stabilize the feedback loop. 38v, low-noise, mos-input, low-power op amp 8 _______________________________________________________________________________________ 1 2 8 7 max 3 4 6 5 MAX9945 in- in+ MAX9945 v out + - + figure 1. shielding the inverting input to reduce leakage MAX9945 in+ in- 10k 10k figure 2. input differential voltage protection
input differential voltage protection during normal op-amp operation, the inverting and non- inverting inputs of the MAX9945 are at approximately the same voltage. the ?2v absolute maximum input differential voltage rating offers sufficient protection for most applications. if there is a possibility of exceeding the input differential voltage specification, in the pres- ence of extremely fast input voltage transients or due to certain application-specific fault conditions, use exter- nal low-leakage pico-amp diodes and series resistors to protect the input stage of the amplifier (see figure 2). the extremely low input bias current of the MAX9945 allows a wide range of input series resistors to be used. if low input voltage noise is critical to the application, size the input series resistors appropriately. MAX9945 38v, low-noise, mos-input, low-power op amp _______________________________________________________________________________________ 9 chip information process: bicmos
MAX9945 38v, low-noise, mos-input, low-power op amp 10 ______________________________________________________________________________________ 16 out v cc 25 v ee n.c. 34 in+ in- tdfn-ep MAX9945 out n.c. v ee 1 2 8 7 n.c. v cc in- in+ n.c. max top view 3 4 6 5 MAX9945 *ep + *ep = exposed pad + pin configurations
MAX9945 38v, low-noise, mos-input, low-power op amp ______________________________________________________________________________________ 11 package type package code document no. 6 tdfn-ep t633-2 21-0137 8 ?ax u8-1 21-0036 package information for the latest package outline information and land patterns, go to www.maxim-ic.com/packages . 6, 8, &10l, dfn thin.eps
MAX9945 38v, low-noise, mos-input, low-power op amp 12 ______________________________________________________________________________________ common dimensions symbol min. max. a 0.70 0.80 d 2.90 3.10 e 2.90 3.10 a1 0.00 0.05 l 0.20 0.40 pkg. code n d2 e2 e jedec spec b [(n/2)-1] x e package variations 0.25 min. k a2 0.20 ref. 2.00 ref 0.250.05 0.50 bsc 2.300.10 10 t1033-1 2.40 ref 0.200.05 - - - - 0.40 bsc 1.700.10 2.300.10 14 t1433-1 1.500.10 mo229 / weed-3 0.40 bsc - - - - 0.200.05 2.40 ref t1433-2 14 2.300.10 1.700.10 t633-2 6 1.500.10 2.300.10 0.95 bsc mo229 / weea 0.400.05 1.90 ref t833-2 8 1.500.10 2.300.10 0.65 bsc mo229 / weec 0.300.05 1.95 ref t833-3 8 1.500.10 2.300.10 0.65 bsc mo229 / weec 0.300.05 1.95 ref 2.300.10 mo229 / weed-3 2.00 ref 0.250.05 0.50 bsc 1.500.10 10 t1033-2 package information (continued) for the latest package outline information and land patterns, go to www.maxim-ic.com/packages .
MAX9945 38v, low-noise, mos-input, low-power op amp maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ____________________ 13 2009 maxim integrated products is a registered trademark of maxim integrated products, inc. 8lumaxd.eps package information (continued) for the latest package outline information and land patterns, go to www.maxim-ic.com/packages .

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