OPA2344

® OPA OPA 344 OPA OPA344 434 4 OPA2344 OPA4344 OPA ® 345 342 OPA345 OPA2345 OPA4345 For most current data sheet and other product information, visit www.burr-brown.com LOW POWER, SINGLE-SUPPLY, RAIL-TO-RAIL OPERATIONAL AMPLIFIERS MicroAmplifier ™ Series FEATURES q q q q RAIL-TO-RAIL INPUT RAIL-TO-RAIL OUTPUT (within 1mV) LOW QUIESCENT CURRENT: 150µA typ MicroSIZE PACKAGES SOT23-5 MSOP-8 TSSOP-14 DESCRIPTION The OPA344 and OPA345 series rail-to-rail CMOS operational amplifiers are designed for precision, lowpower, miniature applications. The OPA344 is unity gain stable, while the OPA345 is optimized for gains greater than or equal to five, and has a gain-bandwidth product of 3MHz. The OPA344 and OPA345 are optimized to operate on a single supply from 2.5V and up to 5.5V with an input common-mode voltage range that extends 300mV beyond the supplies. Quiescent current is only 250µA (max). Rail-to-rail input and output make them ideal for driving sampling analog-to-digital converters. They are also well suited for general purpose and audio applicaitons and providing I/V conversion at the output of D/A converters. Single, dual and quad versions have identical specs for design flexibility. A variety of packages are available. All are specified for operation from –40ºC to 85ºC. A SPICE macromodel is available for design analysis. q GAIN-BANDWIDTH OPA344: 1MHz, G ≥ 1 OPA345: 3MHz, G ≥ 5 q SLEW RATE OPA344: 0.8V/µs OPA345: 2V/µs q THD + NOISE: 0.006% APPLICATIONS q q q q q q q PCMCIA CARDS DATA ACQUISITION PROCESS CONTROL AUDIO PROCESSING COMMUNICATIONS ACTIVE FILTERS TEST EQUIPMENT OPA344, OPA345 Out V– +In 1 2 3 SOT23-5 4 –In 5 V+ OPA4344, OPA4345 Out A –In A 1 2 A +In A 3 4 5 B C 9 8 –In C Out C 6 7 D 12 11 10 +In D –V +In C 14 13 Out D –In D OPA2344, OPA2345 Out A –In A +In A V– 1 2 3 4 A B 8 7 6 5 V+ Out B –In B +In B OPA344, OPA345 NC –In +In V– 1 2 3 4 8 7 6 5 NC V+ Out NC +V +In B –In B Out B SO-8, MSOP-8, 8-Pin DIP (OPA2344 Only) SO-8, 8-Pin DIP (OPA344 Only) TSSOP-14, SO-14, 14-PIn DIP (OPA4344 Only) International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111 Twx: 910-952-1111 • Internet: http://www.burr-brown.com/ • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132 © 2000 Burr-Brown Corporation PDS-1486A Printed in U.S.A. April, 2000 SPECIFICATIONS: VS = 2.7V to 5.5V At TA = +25°C, RL = 10kΩ connected to VS /2 and VOUT = VS /2, unless otherwise noted. Boldface limits apply over the temperature range, TA = –40°C to +85°C. OPA344NA, UA, PA OPA2344EA, UA, PA OPA4344EA, UA, PA PARAMETER OFFSET VOLTAGE Input Offset Voltage Over Temperature vs Temperature vs Power Supply Over Temperature Channel Separation, dc f = 1kHz INPUT BIAS CURRENT Input Bias Current Over Temperature Input Offset Current NOISE Input Voltage Noise Input Voltage Noise Density Current Noise Density INPUT VOLTAGE RANGE Common-Mode Voltage Range Common-Mode Rejection Ratio Over Temperature Common-Mode Rejection Over Temperature Common-Mode Rejection Over Temperature INPUT IMPEDANCE Differential Common-Mode OPEN-LOOP GAIN Open-Loop Voltage Gain Over Temperature Over Temperature FREQUENCY RESPONSE Gain-Bandwidth Product Slew Rate Settling Time, 0.1% 0.01% Overload Recovery Time Total Harmonic Distortion + Noise OUTPUT Voltage Output Swing from Rail(1) Over Temperature Over Temperature Short-Circuit Current Capacitive Load Drive POWER SUPPLY Specified Voltage Range Operating Voltage Range Quiescent Current (per amplifier) Over Temperature TEMPERATURE RANGE Specified Range Operating Range Storage Range Thermal Resistance SOT23-5 Surface Mount MSOP-8 Surface Mount 8-Pin DIP SO-8 Surface Mount TSSOP-14 Surface Mount 14-Pin DIP SO-14 Surface Mount GBW SR VS = 5.5V, 2V Step VS = 5.5V, 2V Step VIN • G = VS VS = 5.5V, VO = 3Vp-p, G = 1, f = 1kHz RL = 100kΩ, AOL ≥ 96dB RL = 100kΩ, AOL ≥ 104dB RL = 100kΩ, AOL ≥ 100dB RL = 5kΩ, AOL ≥ 96dB RL = 5kΩ, AOL ≥ 90dB I SC CLOAD VS IQ VS = 5.5V, IO = 0 2.7 2.5 to 5.5 150 AOL RL = 100kΩ, 10mV < VO < (V+) –10mV RL = 100kΩ, 10mV < VO < (V+) –10mV R L = 5kΩ, 400mV < VO < (V+) –400mV RL = 5kΩ, 400mV < VO < (V+) –400mV CL = 100pF 1 0.8 5 8 2.5 0.006 1 3 40 ±15 See Typical Curve 5.5 250 300 85 125 150 200 150 100 150 100 80 100 MHz V/µs µs µs µs % mV mV mV mV mV mA 104 100 96 90 VOS dVOS/dT PSRR CONDITION VS = +5.5V, VCM = VS/2 MIN TYP ±0.2 ±0.8 ±3 30 0.2 130 IB IOS f = 0.1 to 50kHz f = 10kHz f = 10kHz –0.3 76 74 70 68 66 64 ±0.2 ±10 See Typical Curve ±0.2 ±10 8 30 0.5 (V+) + 0.3 92 84 80 MAX ±1 UNITS mV mV µV/°C µV/V µV/V µV/V dB pA pA pA µVrms nV/√Hz fA/√Hz V dB dB dB dB dB dB Ω || pF Ω || pF dB dB dB dB ±1.2 200 250 VS = 2.7V to 5.5V, VCM < (V+) -1.8V VS = 2.7V to 5.5V, VCM < (V+) -1.8V en in VCM CMRR CMRR CMRR VS = +5.5V, –0.3V < VCM < (V+)-1.8 VS = +5.5V, –0.3V < VCM < (V+)-1.8 VS = +5.5V, –0.3V < VCM < 5.8V VS = +5.5V, –0.3V < VCM < 5.8V VS = +2.7V, –0.3V < VCM < 3V VS = +2.7V, –0.3V < VCM < 3V 1013 || 3 1013 || 6 122 120 THD+N 10 10 400 400 V V µA µA °C °C °C °C/W °C/W °C/W °C/W °C/W °C/W °C/W –40 –55 –65 θJA NOTE: (1) Output voltage swings are measured between the output and power-supply rails. ® OPA344, 2344, 4344 OPA345, 2345, 4345 2 SPECIFICATIONS: VS = 2.7V to 5.5V At TA = +25°C, RL = 10kΩ connected to VS /2 and VOUT = VS /2, unless otherwise noted. Boldface limits apply over the temperature range, TA = –40°C to +85°C. OPA345NA, UA OPA2345EA, UA OPA4345EA, UA PARAMETER OFFSET VOLTAGE Input Offset Voltage Over Temperature vs Temperature vs Power Supply Over Temperature Channel Separation, dc f = 1kHz INPUT BIAS CURRENT Input Bias Current Over Temperature Input Offset Current NOISE Input Voltage Noise Input Voltage Noise Density Current Noise Density INPUT VOLTAGE RANGE Common-Mode Voltage Range Common-Mode Rejection Ratio Over Temperature Common-Mode Rejection Ratio Over Temperature Common-Mode Rejection Ratio Over Temperature INPUT IMPEDANCE Differential Common-Mode OPEN-LOOP GAIN Open-Loop Voltage Gain Over Temperature Over Temperature FREQUENCY RESPONSE Gain-Bandwidth Product Slew Rate Settling Time, 0.1% 0.01% Overload Recovery Time Total Harmonic Distortion + Noise OUTPUT Voltage Output Swing from Rail(1) Over Temperature Over Temperature Short-Circuit Current Capacitive Load Drive POWER SUPPLY Specified Voltage Range Operating Voltage Range Quiescent Current (per amplifier) Over Temperature TEMPERATURE RANGE Specified Range Operating Range Storage Range Thermal Resistance SOT23-5 Surface Mount MSOP-8 Surface Mount SO-8 Surface Mount TSSOP-14 Surface Mount SO-14 Surface Mount GBW SR G = 5, 2V Output Step G = 5, 2V Output Step VIN • G = VS VS = 5.5V, VO = 2.5Vp-p, G = 5, f = 1kHz RL = 100kΩ, AOL ≥ 96dB RL = 100kΩ, AOL ≥ 104dB RL = 100kΩ, AOL ≥ 100dB RL = 5kΩ, AOL ≥ 96dB RL = 5kΩ, AOL ≥ 90dB I SC CLOAD VS IQ VS = 5.5V, IO = 0 2.7 2.5 to 5.5 150 AOL RL = 100kΩ, 10mV < VO < (V+) –10mV RL = 100kΩ, 10mV < VO < (V+) –10mV RL = 5kΩ, 400mV < VO < (V+) –400mV RL = 5kΩ, 400mV < VO < (V+) –400mV CL = 100pF 3 2 1.5 1.6 2.5 0.006 1 3 40 ±15 See Typical Curve 5.5 250 300 85 125 150 200 150 150 100 100 MHz V/µs µs µs µs % mV mV mV mV mV mA 104 100 96 90 VOS dVOS/dT PSRR CONDITION VS = +5.5V, VCM = VS/2 MIN TYP ±0.2 ±0.8 ±3 30 0.2 130 IB IOS f = 0.1 to 50kHz f = 10kHz f = 10kHz –0.3 76 74 70 68 66 64 ±0.2 ±10 See Typical Curve ±0.2 ±10 8 30 0.5 (V+) + 0.3 92 84 80 MAX ±1 UNITS mV mV µV/°C µV/V µV/V µV/V dB pA pA pA µVrms nV/√Hz fA/√ Hz V dB dB dB dB dB dB Ω || pF Ω || pF dB dB dB dB ±1.2 200 250 VS = 2.7V to 5.5V, VCM < (V+) -1.8V VS = 2.7V to 5.5V, VCM < (V+) -1.8V en in VCM CMRR CMRR CMRR VS = +5.5V, –0.3V < VCM < (V+)-1.8 VS = +5.5V, –0.3V < VCM < (V+)-1.8 VS = +5.5V, –0.3V < VCM < 5.8V VS = +5.5V, –0.3V < VCM < 5.8V VS = +2.7V, –0.3V < VCM < 3V VS = +2.7V, –0.3V < VCM < 3V 1013 || 3 1013 || 6 122 120 THD+N 10 10 400 400 V V µA µA °C °C °C °C/W °C/W °C/W °C/W °C/W –40 –55 –65 θJA NOTE: (1) Output voltage swings are measured between the output and power-supply rails. 3 OPA344, 2344, 4344 OPA345, 2345, 4345 ® ABSOLUTE MAXIMUM RATINGS(1) Supply Voltage, V+ to V- ................................................................... 7.5V Signal Input Terminals, Voltage(2) ..................... (V–) –0.5V to (V+) +0.5V Current(2) .................................................... 10mA Output Short-Circuit(3) .............................................................. Continuous Operating Temperature .................................................. –55°C to +125°C Storage Temperature ..................................................... –65°C to +150°C Junction Temperature ...................................................................... 150°C Lead Temperature (soldering, 10s) ................................................. 300°C ESD Tolerance (Human Body Model) ............................................ 4000V NOTES: (1) Stresses above these ratings may cause permanent damage. Exposure to absolute maximum conditions for extended periods may degrade device reliability. These are stress ratings only. Functional operation of the device at these conditions, or beyond the specified operating conditions, is not implied. (2) Input terminals are diode-clamped to the power supply rails. Input signals that can swing more than 0.5V beyond the supply rails should be current-limited to 10mA or less. (3) Short-circuit to ground, one amplifier per package. ELECTROSTATIC DISCHARGE SENSITIVITY This integrated circuit can be damaged by ESD. Burr-Brown recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. PACKAGE/ORDERING INFORMATION PACKAGE DRAWING NUMBER 331 SPECIFIED TEMPERATURE RANGE –40°C to +85°C –40°C to +85°C –40° C to +85°C –40°C to +85°C PACKAGE MARKING B44 ORDERING NUMBER(1) OPA344NA/250 OPA344NA/3K OPA344UA OPA344UA /2K5 OPA344PA OPA2344EA /250 OPA2344EA /2K5 OPA2344UA OPA2344UA/2K5 OPA2344PA OPA4344EA /250 OPA4344EA /2K5 OPA4344UA OPA4344UA/2K5 OPA4344PA OPA345NA/250 OPA345NA/3K OPA345UA OPA345UA/2K5 OPA2345EA/250 OPA2345EA /2K5 OPA2345UA OPA2345UA/2K5 OPA4345EA/250 OPA4345EA /2K5 OPA4345UA OPA4345UA/2K5 TRANSPORT MEDIA Tape and Reel Tape and Reel Rails Tape and Reel Rails Tape and Reel Tape and Reel Rails Tape and Reel Rails Rails Tape and Reel Rails Tape and Reel Rails Tape and Reel Tape and Reel Rails Tape and Reel Tape and Reel Tape and Reel Rails Tape and Reel Tape and Reel Tape and Reel Rails Tape and Reel PRODUCT OPA344NA PACKAGE SOT23-5 " OPA344UA " SO-8 " 182 " " " OPA344UA " OPA344PA OPA2344EA " 8-Pin Dip MSOP-8 " 006 337 " OPA344PA C44 " OPA2344UA " SO-8 " 182 " –40°C to +85°C " OPA2344UA " OPA2344PA OPA4344EA " 8-Pin DIP TSSOP-14 " 006 357 " –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C –40°C to +85°C " –40°C to +85°C " –40°C to +85°C " OPA2344PA OPA4344EA " OPA4344UA " SO-14 " 235 " " " OPA4344UA " OPA4344PA OPA345NA " OPA345UA " OPA2345EA " 14-Pin DIP SOT23-5 " SO-8 " MSOP-8 " 010 331 " 182 " 337 " OPA4344PA A45 " OPA345UA " B45 " OPA2345UA " SO-8 " 182 " –40°C to +85°C " OPA2345UA " OPA4345EA " TSSOP-14 " 357 " –40°C to +85°C " OPA4345EA " OPA4345UA " SO-14 " 235 " –40°C to +85°C " OPA4345UA " " " " " NOTE: (1) Models with a slash (/) are available only in Tape and Reel in the quantities indicated (e.g., /2K5 indicates 2500 devices per reel). Ordering 2500 pieces of “OPA344UA/2K5” will get a single 2500-piece Tape and Reel. ® OPA344, 2344, 4344 OPA345, 2345, 4345 4 TYPICAL PERFORMANCE CURVES At TA = +25°C, VS = +5V, and RL = 10kΩ connected to VS/2, unless otherwise noted. OPEN-LOOP GAIN/PHASE vs FREQUENCY 120 100 OPA344 80 Phase 60 0 30 120 100 OPEN-LOOP GAIN/PHASE vs FREQUENCY 0 30 OPA345 80 Phase 60 90 120 Gain 150 180 10M 20 0 0.1 1 10 100 1k 10k 100k 1M Frequency (Hz) 150 180 10M Gain (dB) Gain (dB) Phase (°) 60 40 Gain 20 0 0.1 1 10 100 1k 10k 100k 1M Frequency (Hz) 90 120 60 40 POWER SUPPLY AND COMMON-MODE REJECTION RATIO vs FREQUENCY 100 +PSRR Maximum Output Voltage (Vp-p) 6 5 4 MAXIMUM OUTPUT VOLTAGE vs FREQUENCY VS = +5.5V VS = +5V OPA344 3 2 1 0 100k VS = +2.7V OPA345 80 Rejection Ratio (dB) CMRR –PSRR 60 40 20 10 10 100 1k Frequency (Hz) 10k 100k 1M Frequency (Hz) 10M CHANNEL SEPARATION vs FREQUENCY 140 VOLTAGE AND CURRENT NOISE SPECTRAL DENSITY vs FREQUENCY 10000 100 Channel Separation (dB) Voltage Noise (nV/√Hz) 120 1000 VN 100 IN 10 100 80 Dual and quad devices. G = 1, all channels. Quad measured channel A to D or B to C—other combinations yield improved rejection. 100 1k 10k Frequency (Hz) 100k 1M 1 60 10 1 10 100 1k 10k 100k 1M Frequency (Hz) 0.1 10M 5 OPA344, 2344, 4344 OPA345, 2345, 4345 Current Noise (fA/√Hz) ® Phase (°) TYPICAL PERFORMANCE CURVES (Cont.) At TA = +25°C, VS = +5V, and RL = 10kΩ connected to VS/2, unless otherwise noted. TOTAL HARMONIC DISTORTION + NOISE vs FREQUENCY 1 OPA344: G = 1 AOL, CMRR, PSRR (dB) OPEN-LOOP GAIN, COMMON-MODE REJECTION RATIO, AND POWER-SUPPLY REJECTION vs TEMPERATURE 140 AOL 120 100 CMRR 80 PSRR 60 40 20 OPA345: G = 5 0.1 THD+N (%) 0.010 0.001 20 100 1k Frequency (Hz) 10k 20k 0 –75 –50 –25 0 25 50 75 100 125 Temperature (°C) INPUT BIAS CURRENT vs TEMPERATURE 10000 QUIESCENT CURRENT AND SHORT-CIRCUIT CURRENT vs TEMPERATURE 200 175 IQ 40 35 30 25 +ISC 100 75 50 25 –ISC 20 15 10 5 0 125 Input Bias Current (pA) 150 135 100 10 1 0.1 –75 –50 –25 0 25 50 75 100 125 Temperature (°C) 0 –75 –50 –25 0 25 50 75 100 Temperature (°C) SLEW RATE vs TEMPERATURE 3.0 2.5 SR– OPA345 SR+ INPUT BIAS CURRENT vs COMMON-MODE VOLTAGE 6 4 Input Bias Current (pA) Slew Rate (V/µs) 2.0 1.5 1.0 0.5 0 –75 –50 –25 2 0 –2 –4 –6 V– Supply V+ Supply OPA344 SR– SR+ Input voltage ≤ –0.3V can cause op amp output to lock up. See text. 0 25 50 75 100 125 –1 0 1 2 3 4 5 6 Temperature (°C) Common-Mode Voltage (V) ® OPA344, 2344, 4344 OPA345, 2345, 4345 6 Short-Circuit Current (mA) Quiescent Current (µA) 1000 TYPICAL PERFORMANCE CURVES (Cont.) At TA = +25°C, VS = +5V, and RL = 10kΩ connected to VS/2, unless otherwise noted. QUIESCENT CURRENT AND SHORT-CIRCUIT CURRENT vs SUPPLY VOLTAGE 160 +ISC 20 OUTPUT VOLTAGE SWING vs OUTPUT CURRENT V+ Short-Circuit Current (mA) Quiescent Current (µA) (V+) – 1 Output Voltage (V) 155 15 –40°C 25°C 85°C (V+) – 2 150 –ISC 10 2 ≈ –40°C 25°C 85°C 0 5 10 Output Current (mA) 15 ≈ 20 IQ 145 5 1 140 2 3 4 Supply Voltage (V) 5 6 0 0 OPEN-LOOP GAIN vs OUTPUT VOLTAGE SWING 140 OFFSET VOLTAGE PRODUCTION DISTRIBUTION Open-Loop Gain (dB) 130 RL = 100kΩ Population –1000 120 RL = 5kΩ 110 100 –800 –600 –400 –200 200 400 600 800 Output Voltage Swing from Rail (mV) Offset Voltage (µV) OFFSET VOLTAGE DRIFT PRODUCTION DISTRIBUTION QUIESCENT CURRENT PRODUCTION DISTRIBUTION Population –10 –8 –6 –4 –2 0 2 4 6 8 10 Population 100 115 130 145 160 175 190 205 220 235 Offset Voltage Drift (µV/°C) Quiescent Current (µA) 7 OPA344, 2344, 4344 OPA345, 2345, 4345 250 ® 1000 120 100 80 60 40 20 0 0 TYPICAL PERFORMANCE CURVES (Cont.) At TA = +25°C, VS = +5V, and RL = 10kΩ connected to VS/2, unless otherwise noted. SMALL-SIGNAL OVERSHOOT vs LOAD CAPACITANCE 50 45 OPA344 SMALL-SIGNAL OVERSHOOT vs LOAD CAPACITANCE 70 OPA345 Small-Signal Overshoot (%) Small-Signal Overshoot (%) 60 G = +5 50 G = –5 40 30 G = –10, +10 20 10 0 40 35 30 25 20 15 10 5 0 1 10 100 Load Capacitance (pF) 1k 10k G = –5 G = –1 G = +1 G = +5 10 100 1k 10k Load Capacitance (pF) LARGE-SIGNAL STEP RESPONSE: OPA344 G = +1, RL = 10kΩ, CL = 100pF OPA344 LARGE-SIGNAL STEP RESPONSE: OPA345 G = +5, RL = 10kΩ, CL = 100pF OPA345 1V/div 1V/div 5µs/div 5µs/div SMALL-SIGNAL STEP RESPONSE: OPA344 G = +1, RL = 10kΩ, CL = 100pF OPA344 SMALL-SIGNAL STEP RESPONSE: OPA345 G = +5, RL = 10kΩ, CL = 100pF OPA345 20mV/div 5µs/div 20mV/div 5µs/div ® OPA344, 2344, 4344 OPA345, 2345, 4345 8 APPLICATIONS INFORMATION OPA344 series op amps are unity gain stable and can operate on a single supply, making them highly versatile and easy to use. OPA345 series op amps are optimized for applications requiring higher speeds with gains of 5 or greater. Rail-to-rail input and output swing significantly increases dynamic range, especially in low supply applications. Figure 1 shows the input and output waveforms for the OPA344 in unity-gain configuration. Operation is from VS = +5V with a 10kΩ load connected to VS/2. The input is a 5Vp-p sinusoid. Output voltage is approximately 4.997Vp-p. Power supply pins should be by passed with 0.01pF ceramic capacitors. OPERATING VOLTAGE OPA344 and OPA345 series op amps are fully specified and guaranteed from +2.7V to +5.5V. In addition, many specifications apply from –40ºC to +85ºC. Parameters that vary significantly with operating voltages or temperature are shown in the Typical Performance Curves. RAIL-TO-RAIL INPUT The input common-mode voltage range of the OPA344 and OPA345 series extends 300mV beyond the supply rails. This is achieved with a complementary input stage—an Nchannel input differential pair in parallel with a P-channel differential pair (see Figure 2). The N-channel pair is active for input voltages close to the positive rail, typically (V+) – 1.3V to 300mV above the positive supply, while the Pchannel pair is on for inputs from 300mV below the negative supply to approximately (V+) –1.3V. There is a small transition region, typically (V+) – 1.5V to (V+) – 1.1V, in which both pairs are on. This 400mV transition region can vary 300mV with process variation. Thus, the transition region (both stages on) can range from (V+) – 1.8V to (V+) – 1.4V on the low end, up to (V+) – 1.2V to (V+) – 0.8V on the high end. Within the 400mV transition region PSRR, CMRR, offset voltage, offset drift, and THD may be degraded compared to operation outside this region. For more information on designing with rail-to-rail input op amps, see Figure 3 “Design Optimization with Rail-to-Rail Input Op Amps.” Input 5V G = +1, VS = +5V 0V Output (inverted on scope) 5µs/div FIGURE 1. Rail-to-Rail Input and Output. 1V/div V+ Reference Current VIN+ VIN– VBIAS1 Class AB Control Circuitry VO VBIAS2 V– (Ground) FIGURE 2. Simplified Schematic. 9 OPA344, 2344, 4344 OPA345, 2345, 4345 ® DESIGN OPTIMIZATION WITH RAIL-TO-RAIL INPUT OP AMPS Rail-to-rail op amps can be used in virtually any op amp configuration. To achieve optimum performance, however, applications using these special double-input-stage op amps may benefit from consideration of their special behavior. In many applications, operation remains within the common-mode range of only one differential input pair. However some applications exercise the amplifier through the transition region of both differential input stages. Although the two input stages are laser trimmed for excellent matching, a small discontinuity may occur in this transition. Careful selection of the circuit configuration, signal levels and biasing can often avoid this transition region. G = 1 Buffer With a unity-gain buffer, for example, signals will traverse this transition at approximately 1.3V below V+ supply and may exhibit a small discontinuity at this point. The common-mode voltage of the non-inverting amplifier is equal to the input voltage. If the input signal always remains less than the transition voltage, no discontinuity will be created. The closed-loop gain of this configuration can still produce a rail-to-rail output. Inverting amplifiers have a constant common-mode voltage equal to VB. If this bias voltage is constant, no discontinuity will be created. The bias voltage can generally be chosen to avoid the transition region. Inverting Amplifier Non-Inverting Gain V+ VB VO V+ VIN VO V+ VO VIN VIN VB VCM = VIN = VO VCM = VIN VCM = VB FIGURE 3. Design Optimization with Rail-to-Rail Input Op Amps. COMMON-MODE REJECTION The CMRR for the OPA344 and OPA345 is specified in several ways so the best match for a given application may be used. First, the CMRR of the device in the common-mode range below the transition region (VCM < (V+) – 1.8V) is given. This specification is the best indicator of the capability of the device when the application requires use of one of the differential input pairs. Second, the CMRR at VS = 5.5V over the entire common-mode range is specified. Third, the CMRR at VS = 2.7V over the entire common-mode range is provided. These last two values include the variations seen through the transition region. INPUT VOLTAGE BEYOND THE RAILS If the input voltage can go more than 0.3V below the negative power supply rail (single-supply ground), special precautions are required. If the input voltage goes sufficiently negative, the op amp output may lock up in an inoperative state. A Schottky diode clamp circuit will prevent this—see Figure 4. The series resistor prevents excessive current (greater than 10mA) in the Schottky diode and in the internal ESD protection diode, if the input voltage can exceed the positive supply voltage. If the signal source is limited to less than 10mA, the input resistor is not required. RAIL-TO-RAIL OUTPUT A class AB output stage with common-source transistors is used to achieve rail-to-rail output. This output stage is capable of driving 600Ω loads connected to any potential ® between V+ and ground. For light resistive loads (> 50kΩ), the output voltage can typically swing to within 1mV from supply rail. With moderate resistive loads (2kΩ to 50kΩ), the output can swing to within a few tens of milli-volts from the supply rails while maintaining high open-loop gain. See the typical performance curve “Output Voltage Swing vs Output Current.” V+ IOVERLOAD 10mA max VIN 1kΩ OPA344 VOUT IN5818 Schottky diode is required only if input voltage can go more than 0.3V below ground. FIGURE 4. Input Current Protection for Voltages Exceeding the Supply Voltage. CAPACITIVE LOAD AND STABILITY The OPA344 in a unity-gain configuration and the OPA345 in gains greater than 5 can directly drive up to 250pF pure capacitive load. Increasing the gain enhances the amplifier’s ability to drive greater capacitive loads. See the typical 10 OPA344, 2344, 4344 OPA345, 2345, 4345 performance curve “Small-Signal Overshoot vs Capacitive Load.” In unity-gain configurations, capacitive load drive can be improved by inserting a small (10Ω to 20Ω) resistor, RS, in series with the output, as shown in Figure 5. This significantly reduces ringing while maintaining dc performance for purely capacitive loads. However, if there is a resistive load in parallel with the capacitive load, a voltage divider is created, introducing a dc error at the output and slightly reducing the output swing. The error introduced is proportional to the ratio RS/RL, and is generally negligible. DRIVING A/D CONVERTERS The OPA344 and OPA345 series op amps are optimized for driving medium-speed sampling A/D converters. The OPA344 and OPA345 op amps buffer the A/D’s input capacitance and resulting charge injection while providing signal gain. Figures 6 shows the OPA344 in a basic noninverting configuration driving the ADS7822. The ADS7822 is a 12-bit, micro-power sampling converter in the MSOP-8 package. When used with the low-power, miniature packages of the OPA344, the combination is ideal for space-limited, lowpower applications. In this configuration, an RC network at the A/D’s input can be used to filter charge injection. Figure 7 shows the OPA2344 driving an ADS7822 in a speech bandpass filtered data acquisition system. This small, low-cost solution provides the necessary amplification and signal conditioning to interface directly with an electret microphone. This circuit will operate with VS = +2.7V to +5V with less than 500µA quiescent current. V+ RS OPA344 VIN 10Ω to 20Ω RL CL VOUT FIGURE 5. Series Resistor in Unity-Gain Configuration Improves Capacitive Load Drive. +5V 0.1µF 0.1µF 8 V+ 500Ω OPA344 VIN 3300pF VIN = 0V to 5V for 0V to 5V output. +In 2 –In 3 GND 4 ADS7822 12-Bit A/D 1 VREF DCLOCK DOUT CS/SHDN 7 6 5 Serial Interface NOTE: A/D Input = 0 to VREF RC network filters high frequency noise. FIGURE 6. OPA344 in Noninverting Configuration Driving ADS7822. V+ = +2.7V to 5V Passband 300Hz to 3kHz R9 510kΩ R1 1.5kΩ R2 1MΩ C1 1000pF R4 20kΩ R7 51kΩ R8 150kΩ C3 33pF VREF 1 1/2 OPA2344 +IN 2 –IN 3 4 8 V+ 7 ADS7822 6 12-Bit A/D 5 DCLOCK DOUT CS/SHDN Serial Interface 1/2 OPA2344 Electret Microphone(1) R3 1MΩ R6 100kΩ C2 1000pF NOTE: (1) Electret microphone powered by R1. R5 20kΩ G = 100 GND FIGURE 7. Speech Bandpass Filtered Data Acquisition System. 11 OPA344, 2344, 4344 OPA345, 2345, 4345 ®