19-4398; Rev 0; 2/09 38V, Low-Noise, MOS-Input, Low-Power Op Amp The MAX9945 operational amplifier features an excellent combination of low operating power and low input voltage 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 400µA quiescent current. The MAX9945 is unity-gain stable and is capable of rail-to-rail output voltage swing. The MAX9945 is ideal for portable medical and industrial applications that require low noise analog front-ends for performance applications such as photodiode transimpedance and chemical sensor interface circuits. The MAX9945 is available in both an 8-pin µMAX® and a space-saving, 6-pin TDFN package, and is specified over the automotive operating temperature range (-40°C to +125°C). Features ♦ +4.75V to +38V Single-Supply Voltage Range ♦ ±2.4V to ±19V Dual-Supply Voltage Range ♦ Rail-to-Rail Output Voltage Swing ♦ 400µA Low Quiescent Current ♦ 50fA Low Input Bias Current √Hz Low Input Current Noise ♦ 1fA/√ √Hz Low Noise ♦ 15nV/√ ♦ 3MHz Unity-Gain Bandwidth ♦ Wide Temperature Range from -40°C to +125°C ♦ Available in Space-Saving, 6-Pin TDFN Package (3mm x 3mm) Ordering Information Applications Medical Pulse Oximetry PART Photodiode Sensor Interface Industrial Sensors and Instrumentation Chemical Sensor Interface TEMP RANGE PINPACKAGE MAX9945ATT+ -40°C to +125°C 6 TDFN-EP* MAX9945AUA+ -40°C to +125°C 8 µMAX TOP MARK AUE — +Denotes a lead(Pb)-free/RoHS-compliant package. High-Performance Audio Line Out *EP = Exposed pad. Active Filters and Signal Processing µMAX is a registered trademark of Maxim Integrated Products, Inc. Typical Operating Circuit VCC PHOTODIODE INOUT MAX9945 SIGNAL CONDITIONING/ FILTERS ADC IN+ VEE ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX9945 General Description MAX9945 38V, Low-Noise, MOS-Input, Low-Power Op Amp ABSOLUTE MAXIMUM RATINGS 8-Pin µMAX (derate 4.8mW/°C above +70°C) Multilayer Board ......................................................387.8mW Package Thermal Resistance (Note 1) θJA .........................................................................206.3°C/W θJC ..............................................................................42°C/W Operating Temperature Range .........................-40°C to +125°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C Supply Voltage (VCC to VEE) ..................................-0.3V to +40V IN+, IN-, OUT Voltage......................(VEE - 0.3V) to (VCC + 0.3V) IN+ to IN- .............................................................................±12V OUT Short Circuit to Ground Duration....................................10s Continuous Input Current into Any Pin .............................±20mA Continuous Power Dissipation (TA = +70°C) 6-Pin TDFN-EP (derate 23.8mW/°C above +70°C) Multilayer Board ....................................................1904.8mW Package Thermal Resistance (Note 1) θJA ..............................................................................42°C/W θJC ................................................................................9°C/W Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a fourlayer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial. Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VCC = +15V, VEE = -15V, VIN+ = VIN- = GND = 0, ROUT = 100kΩ to GND, TA = -40°C to +125°C, typical values are at TA = +25°C, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS DC ELECTRICAL CHARACTERISTICS Input Voltage Range Input Offset Voltage Input Offset Voltage Drift Input Bias Current (Note 3) Common-Mode Rejection Ratio Open-Loop Gain Output Short-Circuit Current 2 VIN+, VIN- VOS Guaranteed by CMRR TA = +25°C VEE VCC 1.2 TA = TMIN to TMAX VEE VCC 1.4 V TA = +25°C ±0.6 TA = TMIN to TMAX ±5 ±8 mV VOS - TC 2 µV/°C IB 50 fA CMRR AOL ISC VCM = VEE to VCC - 1.2V, TA = +25°C 78 94 VCM = VEE to VCC - 1.4V, TA = TMIN to TMAX 78 94 VEE + 0.3V ≤ VOUT ≤ VCC - 0.3V, ROUT = 100kΩ to GND 110 130 VEE + 0.75V ≤ VOUT ≤ VCC - 0.75V, ROUT = 10kΩ to GND 110 dB dB 130 25 _______________________________________________________________________________________ mA 38V, Low-Noise, MOS-Input, Low-Power Op Amp (VCC = +15V, VEE = -15V, VIN+ = VIN- = GND = 0, ROUT = 100kΩ to GND, TA = -40°C to +125°C, typical values are at TA = +25°C, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS TYP MAX TA = TMIN to TMAX VEE + 0.26 VEE + 0.45 ROUT = 100kΩ to GND TA = TMIN to TMAX VEE + 0.05 VEE + 0.15 ROUT = 10kΩ to GND TA = TMIN to TMAX VCC 0.45 VCC 0.24 ROUT = 100kΩ to GND TA = TMIN to TMAX VCC 0.15 VCC 0.03 ROUT = 10kΩ to GND Output Voltage Low Output Voltage High VOL VOH MIN UNITS V V AC ELECTRICAL CHARACTERISTICS Input Current-Noise Density Input Voltage Noise IN VNP-P Input Voltage-Noise Density Gain Bandwidth Slew Rate Capacitive Loading (Note 4) Total Harmonic Distortion VN f = 1kHz 1 fA/√Hz f = 0.1Hz to 10Hz 2 µVP-P f = 100Hz 25 f = 1kHz 16.5 f = 10kHz 15 nV/√Hz GBW 3 MHz SR 2.2 V/µs No sustained oscillations 120 pF VOUT = 4.5VP-P, AV = 1V/V, f = 10kHz, ROUT = 10kΩ to GND 97 dB CLOAD THD POWER-SUPPLY ELECTRICAL CHARACTERISTICS Power-Supply Voltage Range VCC - VEE Power-Supply Rejection Ratio PSRR Quiescent Supply Current ICC Guaranteed by PSRR, VEE = 0 VCC - VEE = +4.75V to +38V TA = +25°C TA = TMIN to TMAX +4.75 82 +38 100 400 V dB 700 850 µA Note 2: All devices are 100% production tested at TA = +25°C. 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. _______________________________________________________________________________________ 3 MAX9945 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VCC = +15V, VEE = -15V, VIN+ = VIN- = GND = 0, ROUT = 100kΩ to GND, TA = -40°C to +125°C, typical values are at TA = +25°C, unless otherwise noted.) TA = +125°C 400 0.15 ISINK = 1.0mA 0.10 TA = +25°C MAX9945 toc03 0.20 VCC - VOH (V) 0.20 500 0.25 MAX9945 toc02 MAX9945 toc01 0.25 VOL - VEE (V) SUPPLY CURRENT (µA) 600 OUTPUT VOLTAGE SWING HIGH vs. TEMPERATURE OUTPUT VOLTAGE SWING LOW vs. TEMPERATURE QUIESCENT SUPPLY CURRENT vs. SUPPLY VOLTAGE AND TEMPERATURE 0.15 ISOURCE = 1.0mA 0.10 ISOURCE = 0.1mA ISINK = 0.1mA 300 0.05 0.05 TA = -40°C 0 0 200 10 15 20 25 30 35 -40 -20 0 20 40 60 80 -40 -20 100 120 0 20 40 60 100 120 TEMPERATURE (°C) TEMPERATURE (°C) INPUT BIAS CURRENT vs. TEMPERATURE INPUT VOLTAGE 0.1Hz TO 10Hz NOISE INPUT VOLTAGE-NOISE DENSITY vs. FREQUENCY MAX9945 toc05 70 60 1000 INPUT VOLTAGE-NOISE DENSITY (nV/ Hz) MAX9945 toc04 80 50 40 30 20 10 0 100 10 -10 -20 0 20 40 60 80 100 120 1 1s/div 1µV/div TEMPERATURE (°C) 1000 TOTAL HARMONIC DISTORTION + NOISE vs. FREQUENCY -50 MAX9945 toc07 VCC - VEE = 30V, 4.5VP-P, RL = 10kΩ 100 FREQUENCY (Hz) TOTAL HARMONIC DISTORTION vs. FREQUENCY -70 10 MAX9945 toc08 -40 VCC - VEE = 30V 4.5VP-P RL = 10kΩ -60 THD+N (dB) THD (dB) -80 -90 -100 -70 -80 -90 -100 -110 100 1000 10,000 FREQUENCY (Hz) 4 80 SUPPLY VOLTAGE (V) MAX9945 toc06 5 IBIAS (pA) MAX9945 38V, Low-Noise, MOS-Input, Low-Power Op Amp 100,000 10 100 1000 10,000 100,000 FREQUENCY (Hz) _______________________________________________________________________________________ 10,000 100,000 38V, Low-Noise, MOS-Input, Low-Power Op Amp INPUT OFFSET VOLTAGE vs. TEMPERATURE INPUT OFFSET VOLTAGE vs. COMMON-MODE VOLTAGE 600 400 200 MAX9945 toc10 800 1000 VCM = VCC - 1.2V INPUT OFFSET VOLTAGE (μV) MAX9945 toc09 INPUT OFFSET VOLTAGE (μV) 1000 800 600 VCM = 0 400 200 VCM = VEE 0 0 -10 -5 0 5 -40 -20 10 20 40 60 80 100 120 TEMPERATURE (°C) OPEN-LOOP GAIN vs. FREQUENCY COMMON-MODE REJECTION RATIO vs. FREQUENCY -20 MAX9945 toc12 120 -30 -40 80 CMRR (dB) OPEN-LOOP GAIN (dB) 0 COMMON-MODE VOLTAGE (V) MAX9945 toc11 -15 40 -50 -60 -70 -80 0 -90 -40 -100 1 10 100 1k 10k 100k 1M 10M 10 100 1k 10k 100k FREQUENCY (Hz) FREQUENCY (Hz) POWER-SUPPLY REJECTION RATIO vs. FREQUENCY RESISTOR ISOLATION vs. CAPACITIVE LOAD MAX9945 toc13 0 -20 1M 10M 10,000 MAX9945 toc14 1m UNSTABLE -60 UNIPOLAR PSRR- UNIPOLAR PSRR+ CLOAD (pF) PSRR (dB) -40 1000 -80 STABLE BIPOLAR PSRR -100 100 -120 1 10 100 1k 10k 100k FREQUENCY (Hz) 1M 10M 1 10 100 RISO (Ω) _______________________________________________________________________________________ 5 MAX9945 Typical Operating Characteristics (continued) (VCC = +15V, VEE = -15V, VIN+ = VIN- = GND = 0, ROUT = 100kΩ to GND, TA = -40°C to +125°C, typical values are at TA = +25°C, unless otherwise noted.) Typical Operating Characteristics (continued) (VCC = +15V, VEE = -15V, VIN+ = VIN- = GND = 0, ROUT = 100kΩ to GND, TA = -40°C to +125°C, typical values are at TA = +25°C, unless otherwise noted.) OP-AMP STABILITY vs. CAPACITIVE AND RESISTIVE LOADS OUTPUT IMPEDANCE vs. FREQUENCY OUTPUT IMPEDANCE (Ω) UNSTABLE 1000 STABLE 100 1000.00 MAX9945 toc16 MAX9945 toc15 PARALLEL LOAD CAPACITANCE (pF) 10,000 100.00 10.00 ACL = 10 1.00 ACL = 1 0.10 0.01 10 10 100 1000 10 10,000 100 1k 10k 100k 1M PARALLEL LOAD RESISTANCE (kΩ) FREQUENCY (Hz) LARGE-SIGNAL RESPONSE vs. FREQUENCY LARGE SIGNAL-STEP RESPONSE 10M RLOAD = 100kΩ 25 MAX9945 toc17 MAX9945 toc18 30 OUTPUT VOLTAGE (VP-P) MAX9945 38V, Low-Noise, MOS-Input, Low-Power Op Amp AV = 1V/V VIN = 10VP-P RL = 10kΩ CL = 100pF +5V 20 VOUT 2.5V/div 15 10 -5V 5 0 1 10 100 1000 4μs/div 10,000 FREQUENCY (kHz) SMALL SIGNAL-STEP RESPONSE LARGE SIGNAL-STEP RESPONSE MAX9945 toc20 MAX9945 toc19 +1V AV = 1V/V VIN = 40mVP-P RL = 100kΩ AV = 1V/V VIN = 2VP-P RL = 10kΩ CL = 100pF +20mV VOUT 500mV/div VOUT 10mV/div -1V -20mV 1μs/div 6 2μs/div _______________________________________________________________________________________ 38V, Low-Noise, MOS-Input, Low-Power Op Amp PIN NAME FUNCTION TDFN-EP µMAX 1 6 OUT Amplifier Output 2 4 VEE Negative Power Supply. Bypass VEE with 0.1µF ceramic and 4.7µF electrolytic capacitors to quiet ground plane if different from VEE. 3 3 IN+ Noninverting Amplifier Input Inverting Amplifier Input 4 2 IN- 5 1, 5, 8 N.C. No Connection. Not internally connected. 6 7 VCC Positive Power Supply. Bypass VCC with 0.1µF ceramic and 4.7µF electrolytic capacitors to quiet ground plane or VEE. — — EP Exposed Pad. Connect to VEE externally. Connect to a large copper plane to maximize thermal performance. Not intended as an electrical connection (TDFN only). Detailed Description The MAX9945 features a combination of low input current 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 photodiode pulse oximeters, pH sensors, capacitive pressure 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 filters 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 2µVP-P (typ). The input stage accepts a wide common-mode range, extending from the negative supply, VEE, to within 1.2V of the positive supply, VCC. Rail-to-Rail Output Stage The MAX9945 output stage swings to within 50mV (typ) of either power-supply rail with a 100kΩ load and provides a 3MHz GBW with a 2.2V/µs slew rate. The device is unity-gain stable, and unlike other devices with a low quiescent current, can drive a 120pF capacitive 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 interfaces to both current-output sensors such as photodiodes 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 feedback capacitors help stabilize the amplifier by canceling 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 photodiode dark current if DC accuracy is important. The high bandwidth and slew rate also allows AC signal processing in certain medical photodiode sensor applications such as pulse oximetry. _______________________________________________________________________________________ 7 MAX9945 Pin Description MAX9945 38V, Low-Noise, MOS-Input, Low-Power Op Amp + 1 8 2 7 3 6 IN4 + MAX9945 IN+ MAX9945 5 μMAX VOUT - Figure 1. Shielding the Inverting Input to Reduce Leakage 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 impedance of the sensor output, a low input bias current with a small temperature variation is very important for these applications. IN+ 10kΩ Power-Supply Decoupling The MAX9945 operates from a +4.75V to +38V, VEE referenced power supply. Bypass the power-supply inputs VCC and VEE to a quiet copper ground plane, with a 0.1µF ceramic capacitor in parallel with a 4.7µF electrolytic capacitor, placed close to the leads. Layout Techniques A good layout is critical to obtaining high performance especially when interfacing with high-impedance sensors. Use shielding techniques to guard against parasitic 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 µMAX 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 voltage differentials that otherwise occur in the rest of the circuit board. This reduces leakage and noise effects, allowing sensitive measurements to be made accurately. 8 MAX9945 10kΩ IN- Figure 2. Input Differential Voltage Protection Take care to also decrease the amount of stray capacitance at the op amp’s 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 Chip Information PROCESS: BiCMOS _______________________________________________________________________________________ 9 MAX9945 Input Differential Voltage Protection During normal op-amp operation, the inverting and noninverting inputs of the MAX9945 are at approximately the same voltage. The ±12V 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 presence of extremely fast input voltage transients or due to certain application-specific fault conditions, use external 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. 38V, Low-Noise, MOS-Input, Low-Power Op Amp MAX9945 Pin Configurations TOP VIEW + + N.C. 1 8 N.C. IN- 2 7 VCC 3 6 OUT VEE 4 5 N.C. MAX9945 IN+ μMAX OUT 1 VEE 2 IN+ 3 MAX9945 6 VCC 5 N.C. 4 IN- *EP TDFN-EP *EP = EXPOSED PAD 10 ______________________________________________________________________________________ 38V, Low-Noise, MOS-Input, Low-Power Op Amp PACKAGE CODE DOCUMENT NO. 6 TDFN-EP T633-2 21-0137 8 µMAX U8-1 21-0036 6, 8, &10L, DFN THIN.EPS PACKAGE TYPE ______________________________________________________________________________________ 11 MAX9945 Package Information 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 Package Information (continued) For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. 12 COMMON DIMENSIONS PACKAGE VARIATIONS SYMBOL MIN. MAX. PKG. CODE N D2 E2 e JEDEC SPEC b [(N/2)-1] x e A 0.70 0.80 T633-2 6 1.50±0.10 2.30±0.10 0.95 BSC MO229 / WEEA 0.40±0.05 1.90 REF D 2.90 3.10 T833-2 8 1.50±0.10 2.30±0.10 0.65 BSC MO229 / WEEC 0.30±0.05 1.95 REF E 2.90 3.10 T833-3 8 1.50±0.10 2.30±0.10 0.65 BSC MO229 / WEEC 0.30±0.05 1.95 REF A1 0.00 0.05 T1033-1 10 1.50±0.10 2.30±0.10 0.50 BSC MO229 / WEED-3 0.25±0.05 2.00 REF L 0.20 0.40 T1033-2 10 1.50±0.10 2.30±0.10 0.50 BSC MO229 / WEED-3 0.25±0.05 2.00 REF k 0.25 MIN. T1433-1 14 1.70±0.10 2.30±0.10 0.40 BSC ---- 0.20±0.05 2.40 REF A2 0.20 REF. T1433-2 14 1.70±0.10 2.30±0.10 0.40 BSC ---- 0.20±0.05 2.40 REF ______________________________________________________________________________________ 38V, Low-Noise, MOS-Input, Low-Power Op Amp 8LUMAXD.EPS α α Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit 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. MAX9945 Package Information (continued) For the latest package outline information and land patterns, go to www.maxim-ic.com/packages.