® OPA350 OPA2350 OPA4350 OPA 350 OPA 235 0 OPA 4 350 O PA 435 0 For most current data sheet and other product information, visit www.burr-brown.com High-Speed, Single-Supply, Rail-to-Rail OPERATIONAL AMPLIFIERS MicroAmplifier ™ Series FEATURES APPLICATIONS ● ● ● ● ● ● ● ● ● ● CELL PHONE PA CONTROL LOOPS ● DRIVING A/D CONVERTERS ● VIDEO PROCESSING ● DATA ACQUISITION ● PROCESS CONTROL ● AUDIO PROCESSING ● COMMUNICATIONS ● ACTIVE FILTERS ● TEST EQUIPMENT RAIL-TO-RAIL INPUT RAIL-TO-RAIL OUTPUT (within 10mV) WIDE BANDWIDTH: 38MHz HIGH SLEW RATE: 22V/µs LOW NOISE: 5nV/√Hz LOW THD+NOISE: 0.0006% UNITY-GAIN STABLE MicroSIZE PACKAGES SINGLE, DUAL, AND QUAD DESCRIPTION OPA350 series rail-to-rail CMOS operational amplifiers are optimized for low voltage, single-supply operation. Rail-to-rail input/output, low noise (5nV/√Hz), and high speed operation (38MHz, 22V/µs) make them ideal for driving sampling analog-to-digital converters. They are also well suited for cell phone PA control loops and video processing (75Ω drive capability) as well as audio and general purpose applications. Single, dual, and quad versions have identical specifications for maximum design flexibility. The OPA350 series operates on a single supply as low as 2.5V with an input common-mode voltage range that extends 300mV below ground and 300mV above the positive supply. Output voltage swing is to within 10mV of the supply rails with a 10kΩ load. Dual and quad designs feature completely independent circuitry for lowest crosstalk and freedom from interaction. The single (OPA350) and dual (OPA2350) come in the miniature MSOP-8 surface mount, SO-8 surface mount, and 8-pin DIP packages. The quad (OPA4350) packages are the space-saving SSOP-16 surface mount and SO-14 surface mount. All are specified from –40°C to +85°C and operate from –55°C to +125°C. SPICE Model available at www.burr-brown.com OPA350 OPA4350 NC 1 8 NC –In 2 7 V+ +In 3 6 Output V– 4 5 NC OPA4350 OPA2350 8-Pin DIP, SO-8, MSOP-8 Out A –In A +In A V– 1 2 3 4 A 7 B 6 5 8-Pin DIP, SO-8, MSOP-8 1 16 Out D –In A 2 15 –In D +In A 3 14 +In D A D Out A 1 14 Out D +V 4 13 –V –In A 2 13 –In D +In B 5 12 +In C +In A 3 12 +In D –In B 6 11 –In C V+ 4 11 V– Out B 7 10 Out C +In B 5 10 +In C NC 8 9 NC –In B 6 9 –In C Out B 7 8 Out C A 8 Out A D V+ B C Out B B –In B +In B C SSOP-16 SO-14 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 © 1998 Burr-Brown Corporation SBOS099 PDS-1470B Printed in U.S.A. March, 1999 SPECIFICATIONS: VS = 2.7V to 5.5V At TA = +25°C, RL = 1kΩ connected to VS /2 and VOUT = VS /2, unless otherwise noted. Boldface limits apply over the specified temperature range, TA = –40°C to +85°C. VS = 5V. OPA350EA, UA, PA OPA2350EA, UA, PA OPA4350EA, UA PARAMETER TYP(1) MAX UNITS VS = 5V ±150 TA = –40°C to +85°C VS = 2.7V to 5.5V, VCM = 0V VS = 2.7V to 5.5V, VCM = 0V dc ±4 40 ±500 ±1 µV mV µV/°C µV/V µV/V µV/V CONDITION OFFSET VOLTAGE Input Offset Voltage TA = –40°C to +85°C vs Temperature vs Power Supply Rejection Ratio TA = –40°C to +85°C Channel Separation (dual, quad) VOS PSRR INPUT BIAS CURRENT Input Bias Current vs Temperature Input Offset Current 0.15 IOS in TA = –40°C to VS = 2.7V, –0.1V < VS = 5.5V, –0.1V < VS = 5.5V, –0.1V < VCM CMRR TA = –40°C to +85°C +85°C VCM < 2.8V VCM < 5.6V VCM < 5.6V –0.1 66 76 74 AOL TA = –40°C to +85°C FREQUENCY RESPONSE Gain-Bandwidth Product Slew Rate Settling Time, 0.1% 0.01% Overload Recovery Time Total Harmonic Distortion + Noise Differential Gain Error Differential Phase Error OUTPUT Voltage Output Swing from Rail(4) TA = –40°C to +85°C TA = –40°C to +85°C Output Current Short-Circuit Current Capacitive Load Drive POWER SUPPLY Operating Voltage Range Minimum Operating Voltage Quiescent Current (per amplifier) TA = –40°C to +85°C TEMPERATURE RANGE Specified Range Operating Range Storage Range Thermal Resistance MSOP-8 Surface Mount SO-8 Surface Mount 8-Pin DIP SO-14 Surface Mount SSOP-16 Surface Mount GBW SR THD+N RL = 10kΩ, 50mV < VO < (V+) –50mV RL = 10kΩ, 50mV < VO < (V+) –50mV RL = 1kΩ, 200mV < VO < (V+) –200mV R L = 1kΩ, 200mV < VO < (V+) –200mV 100 100 100 100 CL = 100pF G=1 G=1 G = ±1, 2V Step G = ±1, 2V Step VIN • G = VS RL = 600Ω, VO = 2.5Vp-p(2), G = 1, f = 1kHz G = 2, RL = 600Ω, VO = 1.4V (3) G = 2, RL = 600Ω, VO = 1.4V (3) VOUT IQ TA = –40°C to +85°C V dB dB dB 1013 || 2.5 1013 || 6.5 Ω || pF Ω || pF 122 dB dB dB dB 120 25 MHz V/µs µs µs µs % % deg 50 50 200 200 mV mV mV mV mA mA 5.5 7.5 8.5 V V mA mA +85 +125 +125 °C °C °C ±40(5) ±80 See Typical Curve CLOAD VS (V+)+0.1 10 I OUT I SC 2.7 2.5 5.2 IO = 0 IO = 0 pA 84 90 38 22 0.22 0.5 0.1 0.0006 0.17 0.17 RL = 10kΩ, AOL ≥ 100dB RL = 10kΩ, A OL ≥ 100dB RL = 1kΩ, AOL ≥ 100dB RL = 1kΩ, AOL ≥ 100dB pA µVrms nV/√Hz nV/√Hz fA/√Hz 4 7 5 4 en INPUT IMPEDANCE Differential Common-Mode OPEN-LOOP GAIN Open-Loop Voltage Gain TA = –40°C to +85°C 150 175 ±0.5 ±10 See Typical Performance Curve ±0.5 ±10 IB NOISE Input Voltage Noise, f = 100Hz to 400kHz Input Voltage Noise Density, f = 10kHz f = 100kHz Current Noise Density, f = 10kHz INPUT VOLTAGE RANGE Common-Mode Voltage Range Common-Mode Rejection Ratio MIN –40 –55 –55 θJA 150 150 100 100 100 °C/W °C/W °C/W °C/W °C/W NOTES: (1) VS = +5V. (2) VOUT = 0.25V to 2.75V. (3) NTSC signal generator used. See Figure 6 for test circuit. (4) Output voltage swings are measured between the output and power supply rails. (5) See typical performance curve, “Output Voltage Swing vs Output Current.” ® OPA350, 2350, 4350 2 ABSOLUTE MAXIMUM RATINGS(1) ELECTROSTATIC DISCHARGE SENSITIVITY Supply Voltage ................................................................................... 5.5V Signal Input Terminals, Voltage(2) .................. (V–) – 0.3V to (V+) + 0.3V Current(2) .................................................... 10mA Output Short Circuit(3) .............................................................. Continuous Operating Temperature .................................................. –55°C to +125°C Storage Temperature ..................................................... –55°C to +125°C Junction Temperature ...................................................................... 150°C Lead Temperature (soldering, 10s) ................................................. 300°C 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. NOTES: (1) Stresses above these ratings may cause permanent damage. Exposure to absolute maximum conditions for extended periods may degrade device reliability. (2) Input terminals are diode-clamped to the power supply rails. Input signals that can swing more than 0.3V beyond the supply rails should be current-limited to 10mA or less. (3) Short circuit to ground, one amplifier per package. PACKAGE/ORDERING INFORMATION PRODUCT PACKAGE PACKAGE DRAWING NUMBER(1) Single OPA350EA MSOP-8 Surface Mount 337 –40°C to +85°C C50 " " " " SO-8 Surface-Mount 182 –40°C to +85°C OPA350UA " " " " OPA350PA 8-Pin DIP 006 –40°C to +85°C OPA350PA Dual OPA2350EA MSOP-8 Surface-Mount 337 –40°C to +85°C D50 " " " " " OPA2350UA SO-8 Surface-Mount 182 –40°C to +85°C OPA2350UA " " " " " OPA2350PA 8-Pin DIP 006 –40°C to +85°C OPA2350PA Quad OPA4350EA SSOP-16 Surface-Mount 322 –40°C to +85°C OPA4350EA " " " " " OPA4350UA SO-14 Surface Mount 235 –40°C to +85°C OPA4350UA " " " " " " OPA350UA " SPECIFIED TEMPERATURE RANGE PACKAGE MARKING ORDERING NUMBER(2) TRANSPORT MEDIA OPA350EA/250 OPA350EA/2K5 OPA350UA OPA350UA/2K5 OPA350PA Tape and Reel Tape and Reel Rails Tape and Reel Rails OPA2350EA/250 OPA2350EA/2K5 OPA2350UA OPA2350UA/2K5 OPA2350PA Tape and Reel Tape and Reel Rails Tape and Reel Rails OPA4350EA/250 OPA4350EA/2K5 OPA4350UA OPA4350UA/2K5 Tape and Reel Tape and Reel Rails Tape and Reel NOTES: (1) For detailed drawing and dimension table, please see end of data sheet, or Appendix C of Burr-Brown IC Data Book. (2) 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 “OPA2350EA/2K5” will get a single 2500-piece Tape and Reel. For detailed Tape and Reel mechanical information, refer to Appendix B of Burr-Brown IC Data Book. The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes no responsibility for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant any BURR-BROWN product for use in life support devices and/or systems. ® 3 OPA350, 2350, 4350 TYPICAL PERFORMANCE CURVES At TA = +25°C, VS = +5V, and RL = 1kΩ connected to VS/2, unless otherwise noted. POWER SUPPLY AND COMMON-MODE REJECTION RATIO vs FREQUENCY OPEN-LOOP GAIN/PHASE vs FREQUENCY 160 0 100 90 140 φ 80 –90 60 G 40 –135 PSRR, CMRR (dB) 100 PSRR 80 –45 Phase (°) Voltage Gain (dB) 120 70 CMRR (VS = +5V VCM = –0.1V to 5.1V) 60 50 40 30 20 20 10 0 –180 0.1 1 10 100 1k 10k 100k 1M 10M 0 100M 10 100 1k Frequency (Hz) 10k 100k 1M 10M Frequency (Hz) INPUT VOLTAGE AND CURRENT NOISE SPECTRAL DENSITY vs FREQUENCY CHANNEL SEPARATION vs FREQUENCY 10k 100k 140 130 100 1k Voltage Noise 100 10 1 10 Channel Separation (dB) 1k Current Noise Current Noise (fA√Hz) Voltage Noise (nV√Hz) 10k 120 110 100 90 80 70 1 10 100 1k 10k 100k 1M 0.1 10M Dual and quad devices. 60 10 100 1k Frequency (Hz) TOTAL HARMONIC DISTORTION + NOISE vs FREQUENCY 0.01 G = 10, 3Vp-p (VO = 1V to 4V) Harmonic Distortion (%) THD+N (%) RL = 600Ω G = 100, 3Vp-p (VO = 1V to 4V) G = 1, 3Vp-p (VO = 1V to 4V) Input goes through transition region 0.001 0.1 (–60dBc) 0.001 (–100dBc) 1k 10k 100k G=1 VO = 2.5Vp-p RL = 600Ω 3rd Harmonic 10k 100k Frequency (Hz) Frequency (Hz) ® OPA350, 2350, 4350 10M 2nd Harmonic 0.0001 (–120dBc) 1k 0.0001 100 1M 0.01 (–80dBc) G = 1, 2.5Vp-p (VO = 0.25V to 2.75V) Input does NOT go through transition region 10 100k HARMONIC DISTORTION + NOISE vs FREQUENCY 1 (–40dBc) 1 0.1 10k Frequency (Hz) 4 1M TYPICAL PERFORMANCE CURVES (CONT) At TA = +25°C, VS = +5V, and RL = 1kΩ connected to VS/2, unless otherwise noted. OPEN-LOOP GAIN vs TEMPERATURE DIFFERENTIAL GAIN/PHASE vs RESISTIVE LOAD 130 0.5 Open-Loop Gain (dB) 0.4 Differential Gain (%) Differential Phase (°) G=2 VO = 1.4V NTSC Signal Generator See Figure 6 for test circuit. Phase 0.3 0.2 Gain 125 RL = 1kΩ RL = 10kΩ 120 RL = 600Ω 115 0.1 110 0 0 100 200 300 400 500 600 –75 700 800 900 1000 –50 –25 COMMON-MODE AND POWER SUPPLY REJECTION RATIO vs TEMPERATURE 100 50 75 100 125 40 CMRR, VS = 5.5V (VCM = –0.1V to +5.6V) 35 90 100 PSRR 70 Slew Rate (V/µs) 90 CMRR, VS = 2.7V (VCM = –0.1V to +2.8V) 30 PSRR (dB) CMRR (dB) 25 SLEW RATE vs TEMPERATURE 110 80 0 Temperature (°C) Resistive Load (Ω) 80 Negative Slew Rate 25 Positive Slew Rate 20 15 10 5 60 –75 0 70 –50 –25 0 25 50 75 100 125 –75 –50 –25 QUIESCENT CURRENT AND SHORT-CIRCUIT CURRENT vs TEMPERATURE 100 6.0 90 5.5 +ISC IQ 60 4.5 50 4.0 40 –25 0 25 50 75 100 125 75 100 5.0 4.5 4.0 3.5 3.0 30 –50 Quiescent Current (mA) 70 Short-Circuit Current (mA) Quiescent Current (mA) 80 –ISC 5.5 3.5 –75 50 Per Amplifier 6.5 5.0 25 QUIESCENT CURRENT vs SUPPLY VOLTAGE 7.0 6.0 0 Temperature (°C) Temperature (°C) 2.0 125 2.5 3.0 3.5 4.0 4.5 5.0 5.5 Supply Voltage (V) Temperature (°C) ® 5 OPA350, 2350, 4350 TYPICAL PERFORMANCE CURVES (CONT) At TA = +25°C, VS = +5V, and RL = 1kΩ connected to VS/2, unless otherwise noted. INPUT BIAS CURRENT vs INPUT COMMON-MODE VOLTAGE 1k 1.5 100 1.0 Input Bias Current (pA) Input Bias Current (pA) INPUT BIAS CURRENT vs TEMPERATURE 10 1 0.5 0.0 0.1 –75 –50 –25 0 25 50 Temperature (°C) 75 100 –0.5 –0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 125 Common-Mode Voltage (V) MAXIMUM OUTPUT VOLTAGE vs FREQUENCY 6 10 5 Output Voltage (Vp-p) Output Impedance (Ω) CLOSED-LOOP OUTPUT IMPEDANCE vs FREQUENCY 100 1 0.1 G = 100 0.01 G = 10 0.001 G=1 10 Maximum output voltage without slew rate-induced distortion. 4 VS = 2.7V 3 2 1 0 100k 0.0001 1 VS = 5.5V 100 1k 10k 100k 1M 10M 100M 1M Frequency (Hz) OUTPUT VOLTAGE SWING vs OUTPUT CURRENT 100M OPEN-LOOP GAIN vs OUTPUT VOLTAGE SWING 140 V+ (V+)–1 Open-Loop Gain (dB) (V+)–2 +25°C –55°C +125°C Depending on circuit configuration (including closed-loop gain) performance may be degraded in shaded region. (V–)+2 +25°C +125°C –55°C IOUT = 2.5mA IOUT = 250µA 130 Output Voltage (V) 10M Frequency (Hz) 120 110 IOUT = 4.2mA 100 90 80 (V–)+1 70 60 (V–) ±10 0 ±20 ±30 ±40 0 Output Current (mA) 40 60 80 100 120 140 160 180 200 Output Voltage Swing from Rails (mV) ® OPA350, 2350, 4350 20 6 TYPICAL PERFORMANCE CURVES (CONT) At TA = +25°C, VS = +5V, and RL = 1kΩ connected to VS/2, unless otherwise noted. OFFSET VOLTAGE DRIFT PRODUCTION DISTRIBUTION OFFSET VOLTAGE PRODUCTION DISTRIBUTION 20 18 Typical distribution of packaged units. Typical production distribution of packaged units. Percent of Amplifiers (%) 18 14 12 10 8 6 4 16 14 12 10 8 6 4 2 2 0 0 0 –500 –450 –400 –350 –300 –250 –200 –150 –100 –50 0 50 100 150 200 250 300 350 400 450 500 Percent of Amplifiers (%) 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Offset Voltage Drift (µV/°C) Offset Voltage (µV) SMALL-SIGNAL OVERSHOOT vs LOAD CAPACITANCE SETTLING TIME vs CLOSED-LOOP GAIN 80 10 70 G=1 Settling Time (µs) 50 G = –1 40 30 G = ±10 20 0.01% 1 10 0.1% 0 0.1 10 100 1k 10k 100k 1M –1 –10 Load Capacitance (pF) Closed-Loop Gain (V/V) SMALL-SIGNAL STEP RESPONSE CL = 100pF LARGE-SIGNAL STEP RESPONSE CL = 100pF –100 1V/div 50mV/div Overshoot (%) 60 200ns/div 100ns/div ® 7 OPA350, 2350, 4350 APPLICATIONS INFORMATION the OPA350 in unity-gain configuration. Operation is from a single +5V supply with a 1kΩ load connected to VS /2. The input is a 5Vp-p sinusoid. Output voltage swing is approximately 4.95Vp-p. OPA350 series op amps are fabricated on a state-of-the-art 0.6 micron CMOS process. They are unity-gain stable and suitable for a wide range of general purpose applications. Rail-to-rail input/output make them ideal for driving sampling A/D converters. They are also well suited for controlling the output power in cell phones. These applications often require high speed and low noise. In addition, the OPA350 series offers a low cost solution for general purpose and consumer video applications (75Ω drive capability). Power supply pins should be bypassed with 0.01µF ceramic capacitors. OPERATING VOLTAGE OPA350 series op amps are fully specified from +2.7V to +5.5V. However, supply voltage may range from +2.5V to +5.5V. Parameters are guaranteed over the specified supply range—a unique feature of the OPA350 series. In addition, many specifications apply from –40°C to +85°C. Most behavior remains virtually unchanged throughout the full operating voltage range. Parameters which vary significantly with operating voltage or temperature are shown in the typical performance curves. Excellent ac performance makes the OPA350 series well suited for audio applications. Their bandwidth, slew rate, low noise (5nV/√Hz), low THD (0.0006%), and small package options are ideal for these applications. The class AB output stage is capable of driving 600Ω loads connected to any point between V+ and ground. Rail-to-rail input and output swing significantly increases dynamic range, especially in low voltage supply applications. Figure 1 shows the input and output waveforms for RAIL-TO-RAIL INPUT The guaranteed input common-mode voltage range of the OPA350 series extends 100mV beyond the supply rails. This is achieved with a complementary input stage—an N-channel 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+) – 1.8V to 100mV above the positive supply, while the P-channel pair is on for inputs from 100mV below the negative supply to approximately (V+) – 1.8V. There is a small transition region, typically (V+) – 2V to (V+) – 1.6V, in which both pairs are on. This 400mV transition region can vary ±400mV with process variation. Thus, the transition region (both input stages on) can range from (V+) – 2.4V to (V+) – 2.0V on the low end, up to (V+) – 1.6V to (V+) – 1.2V on the high end. VS = +5, G = +1, RL = 1kΩ 5V 1.25V/div VIN 0 5V VOUT 0 FIGURE 1. Rail-to-Rail Input and Output. V+ Reference Current VIN+ VIN– VBIAS1 VBIAS2 V– (Ground) FIGURE 2. Simplified Schematic. ® OPA350, 2350, 4350 8 Class AB Control Circuitry VO OPA350 series op amps are laser-trimmed to reduce offset voltage difference between the N-channel and P-channel input stages, resulting in improved commonmode rejection and a smooth transition between the N-channel pair and the P-channel pair. However, within the 400mV transition region PSRR, CMRR, offset voltage, offset drift, and THD may be degraded compared to operation outside this region. performance curve “Small-Signal Overshoot vs Capacitive Load” shows performance with a 1kΩ resistive load. Increasing load resistance improves capacitive load drive capability. FEEDBACK CAPACITOR IMPROVES RESPONSE For optimum settling time and stability with high-impedance feedback networks, it may be necessary to add a feedback capacitor across the feedback resistor, RF, as shown in Figure 4. This capacitor compensates for the zero created by the feedback network impedance and the OPA350’s input capacitance (and any parasitic layout capacitance). The effect becomes more significant with higher impedance networks. A double-folded cascode adds the signal from the two input pairs and presents a differential signal to the class AB output stage. Normally, input bias current is approximately 500fA. However, large inputs (greater than 300mV beyond the supply rails) can turn on the OPA350’s input protection diodes, causing excessive current to flow in or out of the input pins. Momentary voltages greater than 300mV beyond the power supply can be tolerated if the current on the input pins is limited to 10mA. This is easily accomplished with an input resistor as shown in Figure 3. Many input signals are inherently current-limited to less than 10mA, therefore, a limiting resistor is not required. CF RIN RF VIN V+ CIN V+ IOVERLOAD 10mA max RIN • CIN = RF • CF OPA350 VOUT CL OPAx350 CIN VOUT VIN 5kΩ Where CIN is equal to the OPA350’s input capacitance (approximately 9pF) plus any parastic layout capacitance. FIGURE 3. Input Current Protection for Voltages Exceeding the Supply Voltage. FIGURE 4. Feedback Capacitor Improves Dynamic Performance. RAIL-TO-RAIL OUTPUT It is suggested that a variable capacitor be used for the feedback capacitor since input capacitance may vary between op amps and layout capacitance is difficult to determine. For the circuit shown in Figure 4, the value of the variable feedback capacitor should be chosen so that the input resistance times the input capacitance of the OPA350 (typically 9pF) plus the estimated parasitic layout capacitance equals the feedback capacitor times the feedback resistor: A class AB output stage with common-source transistors is used to achieve rail-to-rail output. For light resistive loads (>10kΩ), the output voltage swing is typically a ten millivolts from the supply rails. With heavier resistive loads (600Ω to 10kΩ), the output can swing to within a few tens of millivolts from the supply rails and maintain high openloop gain. See the typical performance curves “Output Voltage Swing vs Output Current” and “Open-Loop Gain vs Output Voltage.” RIN • CIN = RF • CF CAPACITIVE LOAD AND STABILITY OPA350 series op amps can drive a wide range of capacitive loads. However, all op amps under certain conditions may become unstable. Op amp configuration, gain, and load value are just a few of the factors to consider when determining stability. An op amp in unity gain configuration is the most susceptible to the effects of capacitive load. The capacitive load reacts with the op amp’s output impedance, along with any additional load resistance, to create a pole in the small-signal response which degrades the phase margin. where CIN is equal to the OPA350’s input capacitance (sum of differential and common-mode) plus the layout capacitance. The capacitor can be varied until optimum performance is obtained. DRIVING A/D CONVERTERS OPA350 series op amps are optimized for driving medium speed (up to 500kHz) sampling A/D converters. However, they also offer excellent performance for higher speed converters. The OPA350 series provides an effective means of buffering the A/D’s input capacitance and resulting charge injection while providing signal gain. In unity gain, OPA350 series op amps perform well with very large capacitive loads. Increasing gain enhances the amplifier’s ability to drive more capacitance. The typical ® 9 OPA350, 2350, 4350 Figure 5 shows the OPA350 driving an ADS7861. The ADS7861 is a dual, 500kHz 12-bit sampling converter in the tiny SSOP-24 package. When used with the miniature package options of the OPA350 series, the combination is ideal for space-limited applications. For further information, consult the ADS7861 data sheet. from becoming too high, which can cause stability problems when driving capacitive loads. As mentioned previously, the OPA350 has excellent capacitive load drive capability for an op amp with its bandwidth. VIDEO LINE DRIVER Figure 6 shows a circuit for a single supply, G = 2 composite video line driver. The synchronized outputs of a composite video line driver extend below ground. As shown, the input to the op amp should be ac-coupled and shifted positively to provide adequate signal swing to account for these negative signals in a single-supply configuration. OUTPUT IMPEDANCE The low frequency open-loop output impedance of the OPA350’s common-source output stage is approximately 1kΩ. When the op amp is connected with feedback, this value is reduced significantly by the loop gain of the op amp. For example, with 122dB of open-loop gain, the output impedance is reduced in unity-gain to less than 0.001Ω. For each decade rise in the closed-loop gain, the loop gain is reduced by the same amount which results in a ten-fold increase in effective output impedance (see the typical performance curve, “Output Impedance vs Frequency”). The input is terminated with a 75Ω resistor and ac-coupled with a 47µF capacitor to a voltage divider that provides the dc bias point to the input. In Figure 6, this point is approximately (V–) + 1.7V. Setting the optimal bias point requires some understanding of the nature of composite video signals. For best performance, one should be careful to avoid the distortion caused by the transition region of the OPA350’s complementary input stage. Refer to the discussion of rail-to-rail input. At higher frequencies, the output impedance will rise as the open-loop gain of the op amp drops. However, at these frequencies the output also becomes capacitive due to parasitic capacitance. This prevents the output impedance CB1 +5V 2kΩ 2kΩ 2 4 1/4 3 OPA4350 VIN B1 1 0.1µF 0.1µF CB0 24 2kΩ 2kΩ 2 3 6 1/4 5 OPA4350 VIN B0 7 4 5 6 CA1 7 2kΩ 2kΩ 8 9 9 1/4 10 OPA4350 VIN A1 10 8 11 SERIAL DATA A CH B1– SERIAL DATA B CH B0+ BUSY CH B0– CLOCK CH A1+ CS CH A1– 12 VIN A0 13 1/4 OPA4350 14 11 VIN = 0V to 2.45V for 0V to 4.9V output. Choose CB1, CB0, CA1, CA0 to filter high frequency noise. FIGURE 5. OPA4350 Driving Sampling A/D Converter. ® OPA350, 2350, 4350 10 ADS7861 RD CH A0+ CONVST CH A0– A0 REFIN M0 REFOUT M1 1 2kΩ +VA CH B1+ DGND CA0 2kΩ 13 +VD AGND 12 23 22 21 20 19 18 17 16 15 14 Serial Interface RF 1kΩ RG 1kΩ +5V C1 220µF C4 0.1µF + 0.1µF 2 10µF 7 6 OPA350 C2 47µF C5 1000µF ROUT Cable VOUT RL 3 Video In R1 75Ω 4 R2 5kΩ R3 5kΩ +5V (pin 7) R4 5kΩ C3 10µF FIGURE 6. Single-Supply Video Line Driver. +5V 50kΩ (2.5V) 8 RG REF1004-2.5 4 R1 100kΩ R2 25kΩ +5V R3 25kΩ 1/2 OPA2350 R4 100kΩ 1/2 OPA2350 G=5+ VO RL 10kΩ 200kΩ RG FIGURE 7. Two Op-Amp Instrumentation Amplifier With Improved High Frequency Common-Mode Rejection. C1 4.7nF R1 10.5kΩ +2.5V R1 2.74kΩ R2 19.6kΩ +2.5V C1 1830pF VOUT OPA350 RL 20kΩ VIN C2 1nF C2 270pF RL 20kΩ R2 49.9kΩ –2.5V FIGURE 8. 10kHz Low-Pass Filter. VOUT OPA350 VIN –2.5V FIGURE 9. 10kHz High-Pass Filter. ® 11 OPA350, 2350, 4350 IMPORTANT NOTICE Texas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue any product or service without notice, and advise customers to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgment, including those pertaining to warranty, patent infringement, and limitation of liability. TI warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with TI’s standard warranty. Testing and other quality control techniques are utilized to the extent TI deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed, except those mandated by government requirements. Customers are responsible for their applications using TI components. In order to minimize risks associated with the customer’s applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. TI assumes no liability for applications assistance or customer product design. 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