AD8682

Dual/Quad Low Power, High Speed JFET Operational Amplifiers AD8682/AD8684 FEATURES Low supply current: 250 μA/amp maximum High slew rate: 9 V/μs Bandwidth: 3.5 MHz typical Low offset voltage: 1 mV maximum @ 25°C Low input bias current: 20 pA maximum @ 25°C CMRR: 90 dB typical Fast settling time Unity gain stable PIN CONFIGURATIONS OUT A 1 –IN A 2 +IN A 3 V– 4 8 V+ OUT B +IN B 06278-001 06278-002 AD8682 TOP VIEW (Not to Scale) 7 6 5 –IN B Figure 1. 8-Lead SOIC_N and 8-Lead MSOP OUT A 1 –IN A 2 +IN A 3 V+ 4 +IN B 5 –IN B 6 OUT B 7 TOP VIEW (Not to Scale) 14 OUT D 13 –IN D 12 +IN D APPLICATIONS Portable telecommunications Low power industrial and instrumentation Loop filters Active and precision filters Integrators Strain gauge amplifiers Portable medical instrumentation Supply current monitoring AD8684 11 V– 10 +IN C 9 8 –IN C OUT C Figure 2. 14-Lead SOIC_N and 14-Lead TSSOP GENERAL DESCRIPTION The AD8682 and AD8684 are dual and quad low power, precision (1 mV) JFET amplifiers featuring excellent speed at low supply currents. The slew rate is typically 9 V/μs with a supply current under 250 μA per amplifier. These unity-gain stable amplifiers have a typical gain bandwidth of 3.5 MHz. The JFET input stage ensures bias current is typically a few picoamps and below 125 pA maximum over the full temperature operating range. The devices are ideal for portable, low power applications, especially with high source impedance. The devices are unity gain stable and can drive higher capacity loads (G = 1, noninverting), as an example of their excellent dynamic response over a wide range of conditions, delivering dc precision performance at low quiescent currents. Rev. A Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2006–2007 Analog Devices, Inc. All rights reserved. AD8682/AD8684 TABLE OF CONTENTS Features .............................................................................................. 1  Applications....................................................................................... 1  Pin Configurations ........................................................................... 1  General Description ......................................................................... 1  Revision History ............................................................................... 2  Specifications..................................................................................... 3  Electrical Characteristics............................................................. 3  Absolute Maximum Ratings............................................................ 4  Thermal Resistance ...................................................................... 4  ESD Caution...................................................................................4  Typical Performance Characteristics ..............................................5  Applications Information .............................................................. 10  High-Side Signal Conditioning ................................................ 10  Phase Inversion........................................................................... 10  Active Filters ............................................................................... 10  Programmable State Variable Filter ......................................... 11  Outline Dimensions ....................................................................... 12  Ordering Guide .......................................................................... 13  REVISION HISTORY 7/07—Rev. 0 to Rev. A Change to Figure 21 ......................................................................... 8 Change to Figure 31 ......................................................................... 9 10/06—Revision 0: Initial Version Rev. A | Page 2 of 16 AD8682/AD8684 SPECIFICATIONS ELECTRICAL CHARACTERISTICS VS = ±15.0 V, TA = 25°C, VCM = 0 V, unless otherwise noted. Table 1. Parameter INPUT CHARACTERISTICS Offset Voltage AD8682 AD8684 Input Bias Current Input Offset Current Input Voltage Range Common-Mode Rejection Ratio Large Signal Voltage Gain Offset Voltage Drift Bias Current Drift OUTPUT CHARACTERISTICS Output Voltage High Output Voltage Low Short-Circuit Limit Open-Loop Output Impedance POWER SUPPLY Power Supply Rejection Ratio Supply Current/Amplifier Supply Voltage Range DYNAMIC PERFORMANCE Slew Rate Full-Power Bandwidth Settling Time Gain Bandwidth Product Phase Margin NOISE PERFORMANCE Voltage Noise Voltage Noise Density Current Noise Density IB −40°C ≤ TA ≤ +85°C IOS −40°C ≤ TA ≤ +85°C CMRR AVO ΔVOS/ΔT ΔIB/ΔT VOH VOL ISC ZOUT PSRR ISY VS SR B WP tS GBP ØM en p-p en in RL = 10 kΩ RL = 10 kΩ Source Sink f = 1 MHz VS = ±4.5 V to ±18 V, −40°C ≤ TA ≤ +85°C VO = 0 V, −40°C ≤ TA ≤ +85°C +13.5 3 −11 V ≤ VCM ≤ +15 V, −40°C ≤ TA ≤ +85°C RL = 10 kΩ RL = 10 kΩ, −40°C ≤ TA ≤ +85°C −11 70 20 15 90 Symbol VOS +25°C ≤ TA ≤ +85°C −40°C ≤ TA ≤ +25°C +25°C ≤ TA ≤ +85°C −40°C ≤ TA ≤ +25°C 6 Conditions Min Typ 0.35 Max 1 2.5 3 3.5 4 20 125 20 100 +15 Unit mV mV mV mV mV pA pA pA pA V dB V/mV V/mV μV/°C pA/°C V V mA mA Ω dB μA V V/μs kHz μs MHz Degrees μV p-p nV/√Hz pA/√Hz 10 8 +13.9 −13.9 10 −12 200 114 210 −13.5 −8 92 ±4.5 250 ±18 RL = 10 kΩ 1% distortion To 0.01% 7 9 125 1.6 3.5 55 1.3 36 0.01 0.1 Hz to 10 Hz f = 1 kHz Rev. A | Page 3 of 16 AD8682/AD8684 ABSOLUTE MAXIMUM RATINGS Table 2. Parameter Supply Voltage Input Voltage Differential Input Voltage1 Output Short-Circuit Duration Storage Temperature Range Operating Temperature Range Junction Temperature Range Lead Temperature (Soldering, 60 sec) 1 Rating ±18 V ±18 V 36 V Indefinite −65°C to +150°C −40°C to +85°C −65°C to +150°C 300°C THERMAL RESISTANCE Table 3. Package Type 8-Lead MSOP [RM-8] 8-Lead SOIC_N [R-8] 14-Lead TSSOP [RU-14] 14-Lead SOIC [R-14] θJA 210 158 180 120 θJC 45 43 35 36 Unit °C/W °C/W °C/W °C/W For supply voltages less than ±18 V, the absolute maximum input voltage is equal to the supply voltage. ESD CAUTION Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Rev. A | Page 4 of 16 AD8682/AD8684 TYPICAL PERFORMANCE CHARACTERISTICS 80 VS = ±15V TA = 25°C 180 70 60 VS = ±15V TA = 25°C 60 OPEN-LOOP GAIN (dB) 135 50 CLOSED-LOOP GAIN (dB) 40 90 PHASE (Degree) 40 30 20 10 0 –10 –20 AVCL = 100 AVCL = 10 20 45 0 0 AVCL = 1 –20 –45 06278-003 10k 100k FREQUENCY (Hz) 1M 10k 100k FREQUENCY (Hz) 1M 10M Figure 3. AD8682 Open-Loop Gain and Phase vs. Frequency 45 40 35 VS = ±15V RL = 10kΩ 30 Figure 6. AD8682 Closed-Loop Gain vs. Frequency 25 VS = ±15V RL = 10kΩ CL = 50pF –SR OPEN-LOOP GAIN (V/mV) 25 20 15 10 SLEW RATE (V/µs) 30 20 15 10 +SR 5 5 06278-004 –50 –25 0 25 50 75 100 125 –50 –25 0 25 50 75 100 125 TEMPERATURE (°C) TEMPERATURE (°C) Figure 4. AD8682 Open-Loop Gain vs. Temperature 80 1000 Figure 7. Slew Rate vs. Temperature OVERSHOOT (%) +OS 50 40 30 20 10 06278-005 –OS INPUT BIAS CURRENT (pA) VS = ±15V RL = 2kΩ 70 V = 100mV p-p IN AVCL = 1 60 TA = 25°C VS = ±15V VCM = 0V 100 10 1 0 100 200 300 400 500 –50 –25 0 25 50 75 100 125 LOAD CAPACITANCE (pF) TEMPERATURE (°C) Figure 5. Small Signal Overshoot vs. Load Capacitance Figure 8. AD8682 Input Bias Current vs. Temperature Rev. A | Page 5 of 16 06278-008 0 0.1 –75 06278-007 0 –75 0 –75 06278-006 –40 1k –90 10M –30 1k AD8682/AD8684 1000 VS = ±15V TA = 25°C 20 15 TA = 25°C RL = 10kΩ VOH VOLTAGE NOISE DENSITY (nV/√Hz) OUTPUT VOLTAGE SWING (V) 10 5 0 –5 –10 VOL –15 100 10 06278-009 100 1k FREQUENCY (Hz) 10k 0 ±5 ±10 SUPPLY VOLTAGE (V) ±15 ±20 Figure 9. Voltage Noise Density vs. Frequency 1000 VS = ±15V TA = 25°C 1000 Figure 12. Output Voltage Swing vs. Supply Voltage VS = ±15V TA = 25°C INPUT BIAS CURRENT (pA) 100 100 OUTPUT IMPEDANCE (Ω) AVCL = 100 10 AVCL = 10 1 AVCL = 1 10 1 06278-010 –10 –5 0 5 10 15 1k COMMON-MODE VOLTAGE (V) 10k FREQUENCY (Hz) 100k 1M Figure 10. Input Bias Current vs. Common-Mode Voltage 480 TA = 25°C Figure 13. Closed-Loop Output Impedance vs. Frequency 480 475 SUPPLY CURRENT (µA) SUPPLY CURRENT (µA) 475 470 470 465 465 460 460 455 455 06278-011 0 ±5 ±10 SUPPLY VOLTAGE (V) ±15 ±20 –25 0 25 50 75 100 125 TEMPERATURE (°C) Figure 11. AD8682 Supply Current vs. Supply Voltage Figure 14. AD8682 Supply Current vs. Temperature Rev. A | Page 6 of 16 06278-014 450 450 –50 06278-013 0.1 –15 0.1 100 06278-012 1 10 –20 AD8682/AD8684 16 14 VS = ±15V TA = 25°C 30 ABSOLUTE OUTPUT VOLTAGE (V) 12 10 VOH 8 6 4 2 06278-015 MAXIMUM OUTPUT SWING (V p-p) VOL 25 VS = ±15V TA = 25°C RL = 10kΩ AVCL = 1 20 15 10 5 1k LOAD RESISTANCE (Ω) 10k 1k 10k FREQUENCY (Hz) 100k 1M Figure 15. Absolute Output Voltage vs. Load Resistance 140 140 120 100 Figure 18. Maximum Output Swing vs. Frequency VS = ±15V 120 TA = 25°C 100 80 VS = ±15V TA = 25°C +PSRR 80 PSRR (dB) 60 40 20 0 –20 –40 06278-016 CMRR (dB) 60 40 20 0 –20 –40 –PSRR 1k 10k 100k FREQUENCY (Hz) 1M 1k 10k 100k FREQUENCY (Hz) 1M Figure 16. AD8682 PSRR vs. Frequency 14 12 20 18 16 Figure 19. AD8682 CMRR vs. Frequency VS = ±15V TA = 25°C SHORT-CIRCUIT CURRENT (mA) VS = ±15V TA = 25°C 100 × AD8682 (200 OP AMPS) 10 8 6 4 2 0 –50 SINK 14 12 UNITS SOURCE 10 8 6 4 2 –25 0 25 50 75 100 125 06278-017 TEMPERATURE (°C) –0.4 –0.2 0 0.2 VOS (µV) 0.4 0.6 0.8 1.0 Figure 17. AD8682 Short-Circuit Current vs. Temperature Figure 20. AD8682 VOS Distribution Rev. A | Page 7 of 16 06278-020 0 –1.0 –0.8 –0.6 06278-019 –60 100 –60 100 06278-018 0 100 0 100 AD8682/AD8684 400 360 320 280 240 VS = ±15V 300 × AD8682 (600 OP AMPS) INPUT BIAS CURRENT (pA) 1000 100 UNITS 200 160 120 80 40 06278-021 10 1 0 4 8 12 16 20 24 28 32 36 –50 –25 0 25 50 75 100 125 TCVOS (µV/°C) TEMPERATURE (°C) Figure 21. AD8682 TCVOS Distribution SOIC_N Package 50 45 40 OPEN-LOOP GAIN (V/mV) Figure 24. AD8684 Input Bias Current vs. Temperature 950 945 940 935 930 925 920 915 06278-022 35 30 25 20 15 10 5 0 –50 –25 0 25 50 75 100 125 SUPPLY CURRENT (µA) 0 10 20 SUPPLY VOLTAGE (V) 30 40 TEMPERATURE (°C) Figure 22. AD8684 Open-Loop Gain vs. Temperature 60 50 AVCL = 100 Figure 25. AD8684 Relative Supply Current vs. Supply Voltage 950 945 940 935 930 925 920 915 06278-023 VS = ±15V TA = 25°C CLOSED-LOOP GAIN (dB) 30 AVCL = 10 20 10 AVCL = 1 0 –10 –20 SUPPLY CURRENT (µA) 40 1k 10k 100k 1M 10M 100M –25 0 25 50 75 100 125 FREQUENCY (Hz) TEMPERATURE (°C) Figure 23. AD8684 Closed-Loop Gain vs. Frequency Figure 26. AD8684 Supply Current vs. Temperature Rev. A | Page 8 of 16 06278-026 910 –50 06278-025 910 06278-024 0 0.1 –75 AD8682/AD8684 140 VS = ±15V 120 100 PSRR+ PSRR (dB) 35 30 25 40 VS = ±15V TA = 25°C 100 × AD8684 (400 OP AMPS) PSRR– 60 40 20 0 1k UNITS 06278-027 80 20 15 10 5 06278-030 06278-031 10k 100k FREQUENCY (Hz) 1M 10M 0 –1.0 –0.8 –0.6 –0.4 –0.2 0 VOS (µV) 0.2 0.4 0.6 0.8 1.0 Figure 27. AD8684 PSRR vs. Frequency 14 12 SHORT-CIRCUIT CURRENT (mA) 800 700 Figure 30. AD8684 VOS Distribution Package SINK 600 VS = ±15V 300 × AD8684 (1200 OP AMPS) 10 SOURCE 8 6 4 2 0 –50 500 UNITS –25 0 25 50 75 100 125 06278-028 400 300 200 100 0 0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 TCVOS (µV/°C) TEMPERATURE (°C) Figure 28. AD8684 Short-Circuit Current vs. Temperature 140 VS = ±15V 120 100 Figure 31. AD8684 TCVOS Distribution Package CMRR (dB) 80 60 40 20 0 1k 10k 100k FREQUENCY (Hz) 1M 10M Figure 29. AD8684 CMRR vs. Frequency Rev. A | Page 9 of 16 06278-029 AD8682/AD8684 APPLICATIONS INFORMATION The AD8682 and AD8684 are dual and quad JFET op amps that are optimized for high speed at low power. This combination makes these amplifiers excellent choices for battery-powered or low power applications that require above average performance. Applications benefiting from this performance combination include telecommunications, geophysical exploration, portable medical equipment, and navigational instrumentation. PHASE INVERSION Most JFET input amplifiers invert the phase of the input signal if either input exceeds the input common-mode range. For the AD8682/AD8684, negative signals in excess of approximately 14 V cause phase inversion. This is caused by saturation of the input stage leading to the forward-biasing of a drain-gate diode. A simple fix for this in noninverting applications is to place a resistor in series with the noninverting input. This limits the amount of current through the forward-biased diode and prevents shutting down of the output stage. For the AD8682/AD8684, a value of 200 kΩ has been found to work; however, it adds a significant amount of noise. 15 HIGH-SIDE SIGNAL CONDITIONING There are many applications requiring the sensing of signals near the positive rail. The AD8682 and the AD8684 were tested and are guaranteed over a common-mode range (−11 V ≤ VCM ≤ +15 V) that includes the positive supply. The AD8682/AD8684 are commonly used in the sensing of power supply currents and in current sensing applications, such as the partial circuit shown in Figure 32. In this circuit, the voltage drop across a low value resistor, such as the 0.1 Ω shown here, is amplified and compared to 7.5 V. The output can then be used for current limiting. 15V 0.1Ω 500kΩ 100kΩ 100kΩ RL 10 5 VOUT 0 –5 1/2 AD8682 500kΩ 06278-042 –10 –10 –5 0 VIN 5 10 15 Figure 32. High-Side Signal Conditioning Figure 33. AD8682 Phase Reversal ACTIVE FILTERS The wide bandwidth and high slew rates of the AD8682/AD8684 make either one an excellent choice for many filter applications. There are many active filter configurations, but the four most popular configurations are: Butterworth, elliptical, Bessel, and Chebyshev. Each type has a response that is optimized for a given characteristic, as shown in Table 4. Table 4. Type Butterworth Chebyshev Elliptical Bessel (Thompson) Selectivity Moderate Good Best Poor Overshoot Good Moderate Poor Best Phase Nonlinear Linear Amplitude (Pass Band) Maximum flat Equal ripple Equal ripple Amplitude (Stop Band) Equal ripple Rev. A | Page 10 of 16 06278-043 –15 –15 AD8682/AD8684 PROGRAMMABLE STATE VARIABLE FILTER The circuit shown in Figure 34 can be used to accurately program the Q factor; the cutoff frequency, fC; and the gain of a 2-pole state variable filter. The AD8684 has been used in this design because of its high bandwidth, low power, and low noise. This circuit takes only three packages to build because of the quad configuration of the op amps and DACs. The DACs shown are used in voltage mode; therefore, many values are dependent on the accuracy of the DAC only and not on the absolute values of the DAC resistive ladders. As a result, this makes the circuit unusually accurate for a programmable filter. Adjusting DAC 1 changes the signal amplitude across R1; therefore, the DAC attenuation × R1 determines the amount of signal current that charges the integrating capacitor, C1. This cutoff frequency can be expressed as fC = 1 ⎛ D1 ⎞ ⎜ ⎟ 2πR1C1 ⎝ 256 ⎠ where D1 is the digital code for the DAC. DAC3 is used to set the gain. The gain equation is Gain = R4 ⎛ D3 ⎞ ⎜ ⎟ R5 ⎝ 256 ⎠ DAC 2 is used to set the Q of the circuit. Adjusting this DAC controls the amount of feedback from the band-pass node to the input summing node. Note that the digital value of the DAC is in the numerator; therefore, zero code is not a valid operating point. Q= R2 ⎛ 256 ⎞ ⎜ ⎟ R3 ⎝ D2 ⎠ R7 2kΩ R4 2kΩ DAC 3 VIN 1/4 DAC8408 1/4 AD8684 R5 2kΩ 1/4 AD8684 DAC 1 C1 1000pF 1/4 DAC8408 HIGH PASS 1/4 AD8684 R1 2kΩ 1/4 AD8684 DAC 4 C1 1000pF 1/4 DAC8408 1/4 AD8684 R1 2kΩ 1/4 AD8684 LOW PASS R6 2kΩ R3 2kΩ R2 2kΩ BAND PASS DAC 2 1/4 AD8684 1/4 AD8684 1/4 DAC8408 06278-044 Figure 34. Programmable State Variable Filter Rev. A | Page 11 of 16 AD8682/AD8684 OUTLINE DIMENSIONS 5.00 (0.1968) 4.80 (0.1890) 4.00 (0.1574) 3.80 (0.1497) 8 1 5 4 6.20 (0.2440) 5.80 (0.2284) 1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0040) COPLANARITY 0.10 SEATING PLANE 1.75 (0.0688) 1.35 (0.0532) 0.50 (0.0196) 0.25 (0.0099) 8° 0° 0.25 (0.0098) 0.17 (0.0067) 1.27 (0.0500) 0.40 (0.0157) 45° 0.51 (0.0201) 0.31 (0.0122) COMPLIANT TO JEDEC STANDARDS MS-012-A A CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN. Figure 35. 8-Lead Standard Small Outline Package [SOIC_N] Narrow Body (R-8) Dimensions shown in millimeters and (inches) 3.20 3.00 2.80 3.20 3.00 2.80 8 5 1 5.15 4.90 4.65 4 PIN 1 0.65 BSC 0.95 0.85 0.75 0.15 0.00 0.38 0.22 SEATING PLANE 1.10 MAX 8° 0° 0.80 0.60 0.40 0.23 0.08 COPLANARITY 0.10 COMPLIANT TO JEDEC STANDARDS MO-187-AA Figure 36. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters Rev. A | Page 12 of 16 060506-A AD8682/AD8684 8.75 (0.3445) 8.55 (0.3366) 14 1 8 7 4.00 (0.1575) 3.80 (0.1496) 6.20 (0.2441) 5.80 (0.2283) 1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0039) COPLANARITY 0.10 0.51 (0.0201) 0.31 (0.0122) 1.75 (0.0689) 1.35 (0.0531) SEATING PLANE 0.50 (0.0197) 0.25 (0.0098) 8° 0° 0.25 (0.0098) 0.17 (0.0067) 1.27 (0.0500) 0.40 (0.0157) 45° COMPLIANT TO JEDEC STANDARDS MS-012-AB CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN. Figure 37. 14-Lead Standard Small Outline Package [SOIC_N] Narrow Body (R-14) Dimensions shown in millimeters and (inches) 5.10 5.00 4.90 14 8 4.50 4.40 4.30 1 7 6.40 BSC PIN 1 1.05 1.00 0.80 0.65 BSC 1.20 MAX 0.15 0.05 0.30 0.19 0.20 0.09 SEATING COPLANARITY PLANE 0.10 8° 0° 0.75 0.60 0.45 COMPLIANT TO JEDEC STANDARDS MO-153-AB-1 Figure 38. 14-Lead Thin Shrink Small Outline Package [TSSOP] (RU-14) Dimensions shown in millimeters ORDERING GUIDE Model AD8682ARZ 1 AD8682ARZ-REEL1 AD8682ARZ-REEL71 AD8682ARMZ-R21 AD8682ARMZ-REEL1 AD8684ARZ1 AD8684ARZ-REEL1 AD8684ARZ-REEL71 AD8684ARUZ1 AD8684ARUZ-REEL1 1 Temperature Range −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 −40°C to +85°C −40°C to +85°C −40°C to +85°C Package Description 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead MSOP 8-Lead MSOP 14-Lead SOIC_N 14-Lead SOIC_N 14-Lead SOIC_N 14-Lead TSSOP 14-Lead TSSOP Package Option R-8 R-8 R-8 RM-8 RM-8 R-14 R-14 R-14 RU-14 RU-14 060606-A Branding A1K A1K Z= RoHS Compliant Part. Rev. A | Page 13 of 16 AD8682/AD8684 NOTES Rev. A | Page 14 of 16 AD8682/AD8684 NOTES Rev. A | Page 15 of 16 AD8682/AD8684 NOTES ©2006–2007 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D06278-0-7/07(A) Rev. A | Page 16 of 16