OPA4353EA/250G4

® OPA353 OPA2353 OPA4353 OPA 235 3 OPA 435 3 OPA 43 53 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: 44MHz HIGH SLEW RATE: 22V/µs LOW NOISE: 5nV/√Hz LOW THD+NOISE: 0.0006% UNITY-GAIN STABLE MicroSIZE PACKAGES SINGLE, DUAL, AND QUAD DESCRIPTION extends 300mV beyond the supply rails. 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 (OPA353) packages are the tiny 5-lead SOT23-5 surface mount and SO-8 surface mount. The dual (OPA2353) comes in the miniature MSOP-8 surface mount and SO-8 surface mount. The quad (OPA4353) 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. OPA353 series rail-to-rail CMOS operational amplifiers are designed for low cost, miniature applications. They are optimized for low voltage, single-supply operation. Rail-to-rail input/output, low noise (5nV/√Hz), and high speed operation (44MHz, 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 design flexibility. The OPA353 series operates on a single supply as low as 2.5V with an input common-mode voltage range that OPA4353 SPICE Model available at www.burr-brown.com OPA353 NC OPA353 Out 1 5 1 4 NC 2 7 V+ +In 3 6 Output V– 4 5 NC V+ –In SO-8 1 16 Out D –In A 2 15 –In D +In A 3 14 +In D +V 4 13 –V +In B 5 12 +In C A –In V– 2 +In 3 8 Out A D OPA2353 Out A 1 –In A 2 +In A 3 V– 4 A B 8 V+ 7 Out B 6 –In B 5 +In B B C –In B 6 11 –In C Out B 7 10 Out C NC 8 9 NC SSOP-16 SOT-23-5 SO-8, MSOP-8 (SO-14 package not shown) 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 SBOS103 PDS-1479B 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. OPA353NA, UA OPA2353EA, UA OPA4353EA, UA PARAMETER 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 TA = –40°C to +85°C Input Offset Current ±3 TA = –40°C to +85°C VS = 2.7V to 5.5V, VCM = 0V VS = 2.7V to 5.5V, VCM = 0V dc ±5 40 ±0.5 See Typical Curve ±0.5 I OS in VCM CMRR –0.1V < VCM < (V+) – 2.4V VS = 5V, –0.1V < VCM < 5.1V VS = 5V, –0.1V < VCM < 5.1V RL = 10kΩ, 50mV < VO < (V+) – 50mV RL = 10kΩ, 50mV < VO < (V+) – 50mV RL = 1kΩ, 200mV < VO < (V+) – 200mV RL = 1kΩ, 200mV < VO < (V+) – 200mV AOL TA = –40°C to +85°C 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 SOT-23-5 MSOP-8 Surface Mount SO-8 Surface Mount SSOP-16 Surface Mount SO-14 Surface Mount GBW SR THD+N UNITS ±8 mV mV µV/°C µV/V µV/V µV/V ±10 150 175 ±10 pA ±10 pA µVrms nV/√Hz nV/√Hz fA/√Hz 4 7 5 4 en 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 MAX 0.15 –0.1 76 60 58 INPUT IMPEDANCE Differential Common-Mode OPEN-LOOP GAIN Open-Loop Voltage Gain TA = –40°C to +85°C TYP(1) VS = 5V 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 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 RL = 10kΩ, AOL ≥ 100dB RL = 10kΩ, AOL ≥ 100dB RL = 1kΩ, AOL ≥ 100dB RL = 1kΩ, AOL ≥ 100dB IQ V dB dB dB 1013 || 2.5 1013 || 6.5 Ω || pF Ω || pF 122 dB dB dB dB 120 10 25 MHz V/µs µs µs µs % % deg 50 50 200 200 mV mV mV mV mA mA 5.5 8 9 V V mA mA +85 +125 +125 °C °C °C ±40(5) ±80 See Typical Curve CLOAD TA = –40°C to +85°C (V+) + 0.1 44 22 0.22 0.5 0.1 0.0006 0.17 0.17 I OUT I SC VS 86 74 2.7 2.5 5.2 IO = 0 IO = 0 –40 –55 –55 θJA 200 150 150 100 100 °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 Swing.” ® OPA353, 2353, 4353 2 ELECTROSTATIC DISCHARGE SENSITIVITY PIN CONFIGURATION Top View SO-14 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. OPA4353 Out A 1 –In A 2 A 14 Out D 13 –In D D +In A 3 12 +In D V+ 4 11 V– +In B 5 10 +In C B 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. C –In B 6 9 –In C Out B 7 8 Out C ABSOLUTE MAXIMUM RATINGS(1) 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 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 OPA353NA 5-Lead SOT-23-5 331 –40°C to +85°C D53 " " " " " OPA353UA SPECIFIED TEMPERATURE RANGE PACKAGE MARKING ORDERING NUMBER(2) TRANSPORT MEDIA OPA353NA /250 OPA353NA /3K OPA353UA OPA353UA /2K5 Tape and Reel Tape and Reel Rails Tape and Reel OPA2353EA /250 OPA2353EA/2K5 OPA2353UA OPA2353UA/2K5 Tape and Reel Tape and Reel Rails Tape and Reel OPA4353EA /250 OPA4353EA/2K5 OPA4353UA OPA4353UA/2K5 Tape and Reel Tape and Reel Rails Tape and Reel SO-8 Surface Mount 182 –40°C to +85°C OPA353UA " " " " " Dual OPA2353EA MSOP-8 Surface Mount 337 –40°C to +85°C E53 " " " " " OPA2353UA SO-8 Surface Mount 182 –40°C to +85°C OPA2353UA " " " " " Quad OPA4353EA SSOP-16 Surface Mount 322 –40°C to +85°C OPA4353EA " " " " " OPA4353UA SO-14 Surface Mount 235 –40°C to +85°C OPA4353UA " " " " " 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 “OPA2353EA/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 OPA353, 2353, 4353 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 –90 60 G 40 –135 PSRR, CMRR (dB) 100 80 PSRR 80 –45 Phase (°) Voltage Gain (dB) 120 70 60 CMRR (VS = +5V VCM = –0.1V to 5.1V) 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 Dual and Quad Versions 70 1 10 100 1k 10k 100k 1M 0.1 10M 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) ® OPA353, 2353, 4353 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 0 25 50 75 100 125 Temperature (°C) Resistive Load (Ω) COMMON-MODE AND POWER SUPPLY REJECTION RATIO vs TEMPERATURE SLEW RATE vs TEMPERATURE 90 110 40 35 CMRR, VS = 5V (VCM = –0.1V to +5.1V) 100 90 PSRR 60 Slew Rate (V/µs) 70 30 PSRR (dB) CMRR (dB) 80 80 Negative Slew Rate 25 Positive Slew Rate 20 15 10 5 50 –75 70 –50 –25 0 25 50 75 100 0 125 –75 –50 –25 QUIESCENT CURRENT AND SHORT-CIRCUIT CURRENT vs TEMPERATURE 100 6.0 90 5.5 +ISC IQ 60 Quiescent Current (mA) 70 Short-Circuit Current (mA) Quiescent Current (mA) 80 –ISC 5.5 40 3.5 30 3.0 0 25 50 125 4.0 4.0 –25 100 4.5 50 –50 75 5.0 4.5 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) 75 100 125 2.0 Temperature (°C) 2.5 3.0 3.5 4.0 4.5 5.0 5.5 Supply Voltage (V) ® 5 OPA353, 2353, 4353 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 Supply Rails (mV) ® OPA353, 2353, 4353 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 35 25 Typical production distribution of packaged units. Percent of Amplifiers (%) Percent of Units (%) 20 Typical production distribution of packaged units. 30 15 10 5 25 20 15 10 5 0 0 –8 –7 –6 –5 4 –3 –2 –1 0 1 2 3 4 5 6 0 7 8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Offset Voltage Drift (µV/°C) Offset Voltage (mV) SETTLING TIME vs CLOSED-LOOP GAIN SMALL-SIGNAL OVERSHOOT vs LOAD CAPACITANCE 10 80 70 G=1 Settling Time (µs) 50 G = –1 40 30 G = ±10 20 0.01% 1 10 0.1% 0.1 0 10 100 1k 10k 100k ±1 1M ±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 OPA353, 2353, 4353 APPLICATIONS INFORMATION the OPA353 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 is approximately 4.95Vp-p. OPA353 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 well suited for controlling the output power in cell phones. These applications often require high speed and low noise. In addition, the OPA353 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 OPA353 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 OPA353 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 voltages or temperature are shown in the typical performance curves. Excellent ac performance makes the OPA353 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 OPA353 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. ® OPA353, 2353, 4353 8 Class AB Control Circuitry VO FEEDBACK CAPACITOR IMPROVES RESPONSE 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 OPA353’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. 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 OPA353’s input capacitance (and any parasitic layout capacitance). The effect becomes more significant with higher impedance networks. CF RIN RF VIN V+ IOVERLOAD 10mA max OPAx353 V+ CIN VOUT RIN • CIN = RF • CF VIN 5kΩ VOUT OPA353 CL CIN FIGURE 3. Input Current Protection for Voltages Exceeding the Supply Voltage. Where CIN is equal to the OPA353’s input capacitance (approximately 9pF) plus any parastic layout capacitance. RAIL-TO-RAIL OUTPUT FIGURE 4. Feedback Capacitor Improves Dynamic Performance. 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 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 open-loop gain. See the typical performance curves “Output Voltage Swing vs Output Current” and “Open-Loop Gain vs Output Voltage.” 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 OPA353 (typically 9pF) plus the estimated parasitic layout capacitance equals the feedback capacitor times the feedback resistor: CAPACITIVE LOAD AND STABILITY RIN • CIN = RF • CF OPA353 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 OPA353’s input capacitance (sum of differential and common-mode) plus the layout capacitance. The capacitor can be varied until optimum performance is obtained. In unity gain, OPA353 series op amps perform well with large capacitive loads. Increasing gain enhances the amplifier’s ability to drive more capacitance. The typical performance curve “Small-Signal Overshoot vs Capacitive Load” shows performance with a 1kΩ resistive load. Increasing load resistance improves capacitive load drive capability. OPA353 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 OPA353 series provides an effective means of buffering the A/D’s input capacitance and resulting charge injection while providing signal gain. For applications requiring high accuracy, the OPA350 series is recommended. DRIVING A/D CONVERTERS ® 9 OPA353, 2353, 4353 from becoming too high, which can cause stability problems when driving capacitive loads. As mentioned previously, the OPA353 has excellent capacitive load drive capability for an op amp with its bandwidth. Figure 5 shows the OPA353 driving an ADS7861. The ADS7861 is a dual, 12-bit, 500kHz sampling converter in the small SSOP-24 package. When used with the miniature package options of the OPA353 series, the combination is ideal for space-limited and low power applications. For further information consult the ADS7861 data sheet. 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 OPA353’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 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 OPA353’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 OPA4353 VIN B1 0.1µF 0.1µF CB0 24 2kΩ 2kΩ 2 3 6 7 1/4 5 OPA4353 VIN B0 4 5 6 CA1 7 2kΩ 2kΩ 8 9 9 10 8 1/4 10 OPA4353 VIN A1 11 Serial Data A CH B1– Serial Data B CH B0+ BUSY CH B0– CLOCK CH A1+ 1/4 OPA4353 VIN A0 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. OPA4353 Driving Sampling A/D Converter. ® OPA353, 2353, 4353 10 CS ADS7861 CH A1– 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 C4 0.1µF +5V C1 220µF + 0.1µF 10µF 7 C2 47µF Video In C5 1000µF 6 OPA353 ROUT Cable VOUT RL R1 75Ω R2 5kΩ 4 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 R1 100kΩ 4 R2 25kΩ +5V R3 25kΩ 1/2 OPA2353 R4 100kΩ 1/2 OPA2353 G=5+ VOUT RL 10kΩ 200kΩ RG FIGURE 7. Two Op-Amp Instrumentation Amplifier With Improved High Frequency Common-Mode Rejection.