Low Power, Low Noise and Distortion, Rail-to-Rail Output Amplifier ADA4841-1/ADA4841-2 FEATURES CONNECTION DIAGRAMS Low power: 1.1 mA/amp Low wideband noise 2.1 nV/√Hz 1.4 pA/√Hz Low 1/f noise 7 nV/√Hz @ 10 Hz 13 pA/√Hz @ 10 Hz Low distortion: −105 dBc @ 100 kHz, VO = 2 V p-p High speed 80 MHz, −3 dB bandwidth (G = +1) 12 V/μs slew rate 175 ns settling time to 0.1% Low offset voltage: 0.3 mV maximum Rail-to-rail output Power down Wide supply range: 2.7 V to 12 V ADA4841-1 –IN 2 7 +VS +IN 3 6 VOUT –VS 4 05614-001 TOP VIEW NC 1 (Not to Scale) 8 POWER DOWN 5 NC Figure 1. 8-Lead SOIC (R) ADA4841-2 8 +VS –IN1 2 7 OUT2 +IN1 3 6 –IN2 –VS 4 5 +IN2 05614-064 OUT1 1 TOP VIEW (Not to Scale) Figure 2. 8-Lead MSOP (RM-8) and 8-Lead SOIC_N (R) ADA4841-1 Low power, low noise signal processing Battery-powered instrumentation 16-bit PulSAR® ADC drivers VOUT 1 6 +VS –VS 2 5 POWER DOWN +IN 3 4 –IN 05614-099 APPLICATIONS Figure 3. 6-Lead SOT-23 (RJ) GENERAL DESCRIPTION The ADA4841-1/ADA4841-2 provide the performance required to efficiently support emerging 16-bit to 18-bit ADCs and are ideal for portable instrumentation, high channel count, industrial measurement, and medical applications. The ADA4841-1/ ADA4841-2 are ideally suited to drive the AD7685/AD7686, 16-bit PulSAR ADCs. –30 –40 VS = ±5V G = +1 –50 –60 –70 2V p-p THIRD –80 –90 –100 2V p-p SECOND –110 –120 0.01 05614-048 The ADA4841-1/ADA4841-2 output can swing to less than 50 mV of either rail. The input common-mode voltage range extends down to the negative supply. The ADA4841-1/ ADA4841-2 can drive up to 10 pF of capacitive load with minimal peaking. The ADA4841-1/ADA4841-2 packages feature Pb-free lead finish. The amplifiers are rated to work over the industrial temperature range (−40°C to +125°C). HARMONIC DISTORTION (dBc) The ADA4841-1/ADA4841-2 are unity gain stable, low noise and distortion, rail-to-rail output amplifiers that have a quiescent current of 1.5 mA maximum. Despite their low power consumption, these amplifiers offer low wideband voltage noise performance of 2.1 nV/√Hz and 1.4 pA/√Hz current noise, along with excellent spurious-free dynamic range (SFDR) of −105 dBc at 100 kHz. To maintain a low noise environment at lower frequencies, the amplifiers have low 1/f noise of 7 nV/√Hz and 13 pA/√Hz at 10 Hz. 0.1 1 FREQUENCY (MHz) Figure 4. Harmonic Distortion Rev. C 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 Analog Devices, Inc. All rights reserved. ADA4841-1/ADA4841-2 TABLE OF CONTENTS Features .............................................................................................. 1 Headroom Considerations........................................................ 14 Applications....................................................................................... 1 Capacitance Drive ...................................................................... 15 Connection Diagrams...................................................................... 1 Input Protection ......................................................................... 15 General Description ......................................................................... 1 Power-Down Operation ............................................................ 16 Revision History ............................................................................... 2 Applications..................................................................................... 17 Specifications..................................................................................... 3 Typical Performance Values...................................................... 17 Absolute Maximum Ratings............................................................ 6 16-Bit ADC Driver..................................................................... 17 Thermal Resistance ...................................................................... 6 Reconstruction Filter ................................................................. 17 ESD Caution.................................................................................. 6 Layout Considerations............................................................... 18 Typical Performance Characteristics ............................................. 7 Ground Plane.............................................................................. 18 Theory of Operation ...................................................................... 13 Power Supply Bypassing ............................................................ 18 Amplifier Description................................................................ 13 Outline Dimensions ....................................................................... 19 DC Errors .................................................................................... 13 Ordering Guide .......................................................................... 20 Noise Considerations ................................................................. 13 REVISION HISTORY 3/06—Rev. B to Rev. C Added SOT-23 Package .....................................................Universal Changes to General Description .................................................... 1 Changes to Table 1............................................................................ 3 Changes to Table 2............................................................................ 4 Changes to Table 3............................................................................ 5 Changes to Input Protection Section ........................................... 15 Changes to Ordering Guide .......................................................... 20 10/05—Rev. A to Rev. B Added ADA4841-2.............................................................Universal Changes to General Description and Features ............................. 1 Changes to Table 1............................................................................ 3 Changes to Table 2............................................................................ 4 Changes to Table 3............................................................................ 5 Changes to Table 4, Table 5, and Figure 4 ..................................... 6 Changes to Figure 6.......................................................................... 7 Changes to Figure 12, Figure 13, Figure 15, and Figure 16......... 8 Deleted Figure 25; Renumber Sequentially................................. 10 Changes to Figure 24 and Figure 28............................................. 10 Changes to Figure 31...................................................................... 11 Inserted Figure 37; Renumber Sequentially................................ 12 Changes to Amplifier Description Section and Figure 39 ........ 13 Changed DC Performance Considerations Section to DC Errors Section...................................................................... 13 Changes to Noise Considerations Section .................................. 14 Changes to Headroom Considerations Section and Figure 39 15 Changes to Power-Down Operation Section.............................. 16 Changes to 16-Bit ADC Driver Section, Figure 48, and Figure 49 ................................................................ 17 Changes to Power Supply Bypassing Section ............................. 18 Updated Outline Dimensions....................................................... 19 Changes to Ordering Guide .......................................................... 20 9/05—Rev. 0 to Rev. A Changes to Features ..........................................................................1 Changes to Figure 2...........................................................................1 Changes to Figure 12.........................................................................8 Changes to Figure 40...................................................................... 14 Changes to Headroom Considerations Section ......................... 15 7/05—Revision 0: Initial Version Rev. C | Page 2 of 20 ADA4841-1/ADA4841-2 SPECIFICATIONS TA = 25°C, VS = ±5 V, RL = 1 kΩ, Gain = +1, unless otherwise noted. Table 1. Parameter DYNAMIC PERFORMANCE −3 dB Bandwidth Slew Rate Settling Time to 0.1% Settling Time to 0.01% NOISE/HARMONIC PERFORMANCE Harmonic Distortion HD2/HD3 Input Voltage Noise Input Current Noise DC PERFORMANCE Input Offset Voltage Input Offset Voltage Drift Input Bias Current Input Offset Current Open-Loop Gain INPUT CHARACTERISTICS Input Resistance, Common Mode Input Resistance, Differential Mode Input Capacitance, Common Mode Input Capacitance, Differential Mode Input Common-Mode Voltage Range Common-Mode Rejection Ratio (CMRR) MATCHING CHARACTERISTICS (ADA4841-2) Input Offset Voltage Input Bias Current POWER DOWN PIN (ADA4841-1) POWER DOWN Voltage POWER DOWN Voltage Input Current Enable Power Down Switching Speed Enable Power Down OUTPUT CHARACTERISTICS Output Voltage Swing Output Current Limit Capacitive Load Drive POWER SUPPLY Operating Range Quiescent Current/Amplifier Positive Power Supply Rejection Ratio Negative Power Supply Rejection Ratio Conditions Min Typ VO = 0.02 V p-p VO = 2 V p-p G = +1, VO = 9 V step, RL = 1 kΩ G = +1, VO = 8 V step G = +1, VO = 8 V step 58 80 3 13 650 1000 MHz MHz V/μs ns ns fC = 100 kHz, VO = 2 V p-p, G = +1 fC = 1 MHz, VO = 2 V p-p f = 100 kHz f = 100 kHz −111/−105 −80/−67 2.1 1.4 dBc dBc nV/√Hz pA/√Hz VO = ±4 V 40 1 3 0.1 120 12 103 Max 300 5.3 0.5 90 25 1 3 Unit μV μV/°C μA μA dB 115 MΩ kΩ pF pF V dB 70 60 μV nA Enabled Power down >3.6 <3.2 V V POWER DOWN = +5 V POWER DOWN = −5 V 1 −13 VCM = Δ 4 V G > +1 Sourcing, VIN = +VS , RL = 50 Ω to GND Sinking, VIN = −VS , RL = 50 Ω to GND 30% overshoot −5.1 95 ±4.9 +4 Rev. C | Page 3 of 20 95 96 μA μA 1 40 μs μs ±4.955 30 60 15 V mA mA pF 2.7 POWER DOWN = +5 V POWER DOWN = −5 V +VS = +5 V to +6 V, −VS = −5 V +VS = +5 V, −VS = −5 V to +6 V 2 −30 1.2 40 110 120 12 1.5 90 V mA μA dB dB ADA4841-1/ADA4841-2 TA = 25°C, VS = 5 V, RL = 1 kΩ, Gain = +1, VCM = 2.5 V, unless otherwise noted. Table 2. Parameter DYNAMIC PERFORMANCE −3 dB Bandwidth Slew Rate Settling Time to 0.1% Settling Time to 0.01% NOISE/HARMONIC PERFORMANCE Harmonic Distortion HD2/HD3 Input Voltage Noise Input Current Noise Crosstalk DC PERFORMANCE Input Offset Voltage Input Offset Voltage Drift Input Bias Current Input Offset Current Open-Loop Gain INPUT CHARACTERISTICS Input Resistance, Common Mode Input Resistance, Differential Mode Input Capacitance, Common Mode Input Capacitance, Differential Mode Input Common-Mode Voltage Range Common-Mode Rejection Ratio (CMRR) MATCHING CHARACTERISTICS (ADA4841-2) Input Offset Voltage Input Bias Current POWER DOWN PIN (ADA4841-1) POWER DOWN Voltage POWER DOWN Voltage Input Current Enable Power Down Switching Speed Enable Power Down OUTPUT CHARACTERISTICS Output Voltage Swing Output Current Limit Capacitive Load Drive POWER SUPPLY Operating Range Quiescent Current/Amplifier Positive Power Supply Rejection Ratio Negative Power Supply Rejection Ratio Conditions Min Typ VO = 0.02 V p-p VO = 2 V p-p G = +1, VO = 4 V step, RL = 1 kΩ G = +1, VO = 2 V step G = +1, VO = 2 V step 54 80 3 12 175 550 MHz MHz V/μs ns ns fC = 100 kHz, VO = 2 V p-p fC = 1 MHz, VO = 2 V p-p f = 100 kHz f = 100 kHz f = 100 kHz −109/−105 −78/−66 2.1 1.4 −117 dBc dBc nV/√Hz pA/√Hz dB VO = 0.5 V to 4.5 V 40 1 3 0.1 124 10 103 Max 300 5.3 0.4 90 25 1 3 Unit μV μV/°C μA μA dB 115 MΩ kΩ pF pF V dB 70 70 μV nA Enabled Power down >3.6 <3.2 V POWER DOWN = 5 V POWER DOWN = 0 V 1 −13 VCM = Δ 1.5 V G > +1 Sourcing, VIN = +VS, RL = 50 Ω to VCM Sinking, VIN = −VS, RL = 50 Ω to VCM 30% overshoot −0.1 88 0.08 to 4.92 +4 Rev. C | Page 4 of 20 95 96 μA μA 1 40 μs μs 0.029 to 4.974 30 60 15 V mA mA pF 2.7 POWER DOWN = 5 V POWER DOWN = 0 V +VS = +5 V to +6 V, −VS = 0 V +VS = +5 V, −VS = 0 V to −1 V 2 −30 1.1 35 110 120 12 1.4 70 V mA μA dB dB ADA4841-1/ADA4841-2 TA = 25°C, VS = 3 V, RL = 1 kΩ, Gain =+1, VCM = 1.5 V, unless otherwise noted. Table 3. Parameter DYNAMIC PERFORMANCE −3 dB Bandwidth Slew Rate Settling Time to 0.1% Settling Time to 0.01% NOISE/HARMONIC PERFORMANCE Harmonic Distortion HD2/HD3 Input Voltage Noise Input Current Noise DC PERFORMANCE Input Offset Voltage Input Offset Voltage Drift Input Bias Current Input Offset Current Open-Loop Gain INPUT CHARACTERISTICS Input Resistance, Common Mode Input Resistance, Differential Mode Input Capacitance, Common Mode Input Capacitance, Differential Mode Input Common-Mode Voltage Range Common-Mode Rejection Ratio (CMRR) MATCHING CHARACTERISTICS (ADA4841-2) Input Offset Voltage Input Bias Current POWER DOWN PIN (ADA4841-1) POWER DOWN Voltage POWER DOWN Voltage Input Current Enable Power Down Switching Speed Enable Power Down OUTPUT CHARACTERISTICS Output Voltage Swing Output Current Limit Capacitive Load Drive POWER SUPPLY Operating Range Quiescent Current/Amplifier Positive Power Supply Rejection Ratio Negative Power Supply Rejection Ratio Conditions Min Typ VO = 0.02 V p-p G = +1, VO = 2 V step, RL = 1 kΩ G = +1, VO = 1 V step G = +1, VO = 1 V step 52 10 80 12 120 250 MHz V/μs ns ns fC = 100 kHz, VO = 1 V p-p fC = 1 MHz, VO = 1 V p-p f = 100 kHz f = 100 kHz −97/−100 −79/−80 2.1 1.4 dBc dBc nV/√Hz pA/√Hz VO = 0.5 V to 2.5 V 40 1 3 0.1 123 101 Max 300 5.3 0.5 90 25 1 3 Unit μV μV/°C μA μA dB 115 MΩ kΩ pF pF V dB 70 60 μV nA Enabled Power down >1.6 <1.2 V POWER DOWN = 3 V POWER DOWN = 0 V 1 −10 −0.1 86 VCM = Δ 0.4 V G > +1 Sourcing, VIN = +VS, RL = 50 Ω to VCM Sinking, VIN = −VS, RL = 50 Ω to VCM 30% overshoot 0.045 to 2.955 +2 Rev. C | Page 5 of 20 95 96 μA μA 1 40 μs μs 0.023 to 2.988 30 60 30 V mA mA pF 2.7 POWER DOWN = 3 V POWER DOWN = 0 V +VS = +3 V to +4 V, −VS = 0 V +VS = +3 V, −VS = 0 V to −1 V 2 −30 1.1 25 110 120 12 1.3 60 V mA μA dB dB ADA4841-1/ADA4841-2 ABSOLUTE MAXIMUM RATINGS Table 4. Parameter Supply Voltage Power Dissipation Common-Mode Input Voltage Differential Input Voltage Storage Temperature Range Operating Temperature Range Lead Temperature Junction Temperature The power dissipated in the package (PD) is the sum of the quiescent power dissipation and the power dissipated in the die due to the amplifier’s drive at the output. The quiescent power is the voltage between the supply pins (VS) times the quiescent current (IS). Rating 12.6 V See Figure 5 −VS − 0.5 V to +VS + 0.5 V ±1.8 V −65°C to +125°C −40°C to +85°C JEDEC J-STD-20 150°C PD = Quiescent Power + (Total Drive Power − Load Power) ⎛V V PD = (VS × I S ) + ⎜⎜ S × OUT RL ⎝ 2 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. ⎞ VOUT 2 ⎟− ⎟ RL ⎠ RMS output voltages should be considered. If RL is referenced to −VS, as in single-supply operation, the total drive power is VS × IOUT. If the rms signal levels are indeterminate, consider the worst case, when VOUT = VS/4 for RL to midsupply. PD = (VS × I S ) + (VS /4 )2 RL In single-supply operation with RL referenced to −VS, worst case is VOUT = VS/2. THERMAL RESISTANCE θJA is specified for the worst-case conditions, that is, θJA is specified for device soldered in circuit board for surface-mount packages. Airflow increases heat dissipation, effectively reducing θJA. In addition, more metal directly in contact with the package leads and through holes under the device reduces θJA. Table 5. Thermal Resistance θJA 125 130 170 Figure 5 shows the maximum safe power dissipation in the package vs. the ambient temperature for the 8-lead MSOP (145°C/W), 8-lead SOIC_N (125°C/W) and the 6-lead SOT-23 (170°C/W) on a JEDEC standard 4-layer board. θJA values are approximations. Unit °C/W °C/W °C/W 2.0 The maximum safe power dissipation for the ADA4841-1/ ADA4841-2 is limited by the associated rise in junction temperature (TJ) on the die. At approximately 150°C, which is the glass transition temperature, the plastic changes its properties. Even temporarily exceeding this temperature limit may change the stresses that the package exerts on the die, permanently shifting the parametric performance of the amplifiers. Exceeding a junction temperature of 150°C for an extended period can result in changes in silicon devices, potentially causing degradation or loss of functionality. MAXIMUM POWER DISSIPATION (W) Maximum Power Dissipation 1.5 SOIC MSOP 1.0 SOT-23 0.5 05614-061 Package Type 8-lead SOIC_N 8-lead MSOP 6-Lead SOT-23 0 –55 –45 –35 –25 –15 –5 5 15 25 35 45 55 65 75 85 95 105 115 125 AMBIENT TEMPERATURE (°C) Figure 5. Maximum Power Dissipation vs. Temperature for a 4-Layer Board ESD CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although this product features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. Rev. C | Page 6 of 20 ADA4841-1/ADA4841-2 TYPICAL PERFORMANCE CHARACTERISTICS RL = 1 kΩ, unless otherwise noted. 3 VOUT = 2V pp VS = 5V G = +1 VS = 5V VIN = 20mV p-p G = +1 +25°C –40°C 0 0 GAIN (dB) G = +10 –3 G = +2 –6 +125°C –3 –6 –12 0.1 –9 0.1 10 1 05614-028 –9 05614-021 NORMALIZED CLOSED-LOOP GAIN (dB) 3 1 FREQUENCY (MHz) Figure 6. Large Signal Frequency Response vs. Gain 6 VIN = 20mV p-p G = +1 VS = 5V 100 10 FREQUENCY (MHz) Figure 9. Small Signal Frequency Response vs. Temperature 2 20pF 20pF WITH 100Ω SNUBBER 1 VIN = 20mV p-p G = +1 VS = +3V VS = +5V VS = ±5V 0 –1 0 0pF –3 GAIN (dB) 10pF –2 –3 –4 05614-026 –6 –9 0.1 1 10 –5 05614-029 CLOSED-LOOP GAIN (dB) 3 –6 0.1 100 1 FREQUENCY (MHz) Figure 10. Small Signal Frequency Response vs. Supply Voltage Figure 7. Small Signal Frequency Response vs. Capacitive Load VIN = 20mV p-p VS = 5V G = –1 3 G = +1 VS = ±5V G = +1 10mV p-p 0 G = +10 0 GAIN (dB) –3 –6 –3 2V p-p 400mV p-p 20mV p-p –6 100mV p-p –12 0.1 1 10 100 –9 0.1 05614-014 –9 05614-027 NORMALIZED CLOSED-LOOP GAIN (dB) 3 100 10 FREQUENCY (MHz) 1 10 FREQUENCY (MHz) FREQUENCY (MHz) Figure 8. Small Signal Frequency Response vs. Gain Figure 11. Frequency Response for Various VOUT Rev. C | Page 7 of 20 100 ADA4841-1/ADA4841-2 –20 –40 –40 100 PHASE 80 –60 –80 60 40 –100 20 –120 0 –140 –20 10 100 1k 10k 100k 1M 10M 05614-042 OPEN-LOOP GAIN (dB) –30 –160 100M FREQUENCY (Hz) VOUT = 2V p-p G = +2 –50 +5V SECOND –60 –70 +3V SECOND –80 –90 +3V THIRD –100 ±5V THIRD –110 +5V THIRD –120 –130 0.01 05614-047 MAGNITUDE 120 0 HARMONIC DISTORTION (dBc) VS = 5V OPEN-LOOP PHASE (Degrees) 140 ±5V SECOND 1 0.1 FREQUENCY (MHz) Figure 15. Harmonic Distortion vs. Frequency for Various Supplies Figure 12. Open-Loop Gain and Phase vs. Frequency –30 10 VS = + 5V VOUT = 2V p-p VS = ±5V –50 VOLTAGE NOISE (nV/ Hz) G = +5 THIRD –60 –70 –90 G = +2 SECOND G = +5 SECOND –100 G = +1 SECOND –110 G = +1 THIRD –120 G = +2 THIRD –130 0.01 0.1 1 1 10 FREQUENCY (MHz) 05614-034 –80 05614-045 HARMONIC DISTORTION (dBc) –40 100 1k 10k 100k 1M 10M FREQUENCY (Hz) Figure 16. Voltage Noise vs. Frequency Figure 13. Harmonic Distortion vs. Frequency for Various Gains –30 –40 100 VS = ±5V G = +1 VS = ±5V CURRENT NOISE (pA/ Hz) –50 8V p-p THIRD –60 –70 4V p-p THIRD 4V p-p SECOND –90 –100 2V p-p THIRD –110 –120 0.01 1 2V p-p SECOND 0.1 1 0.1 10 FREQUENCY (MHz) 05614-018 –80 10 05614-046 HARMONIC DISTORTION (dBc) 8V p-p SECOND 100 1k 10k 100k FREQUENCY (Hz) Figure 14. Harmonic Distortion vs. Frequency for Various Output Voltages Rev. C | Page 8 of 20 Figure 17. Current Noise vs. Frequency 1M ADA4841-1/ADA4841-2 55 0.25 45 0.24 G = +2 TIME = 50ns/DIV VS = +3V VS = +5V 40 OUTPUT VOLTAGE (V) 35 30 25 20 15 10 0.23 VS = ±5V 0.22 0.21 05614-053 0.20 5 0 –5 –4 –2 0 2 05614-033 NUMBER OF PARTS COUNT = 190 50 x = 0.36μV/°C σ = 1.21μV/°C 0.19 6 4 OFFSET DRIFT DISTRIBUTION (μV/°C) Figure 21. Small Signal Transient Response for Various Supplies Figure 18. Input Offset Voltage Drift Distribution 10 0.15 G = +1 VS = 5V 9 0.14 7 OUTPUT VOLTAGE (V) NONLINEARITY (μV) 8 6 5 4 3 G = +2 VIN = 20mV p-p TIME = 50ns/DIV 0pF 0.13 10pF 0.12 0.11 2 0 1 2 3 0.09 5 4 05614-031 0 20pF 47pF 0.10 05614-013 1 VIN (V) Figure 19. Nonlinearity vs. VIN 0.130 0.125 60 0.120 OUTPUT VOLTAGE (V) 80 40 20 0 0.115 –40 0.095 –2 0 2 4 VS = 5V 0.105 0.100 –4 VS = 3V 0.110 –20 –60 –6 G = +1 TIME = 50ns/DIV 0.090 6 VOUT (V) Figure 20. Input Error Voltage vs. Output Voltage Figure 23. Small Signal Transient Response for Various Supplies Rev. C | Page 9 of 20 05614-030 VS = ±5 05614-036 VOFFSET (μV) 100 Figure 22. Small Signal Transient Response for Various Capacitive Loads ADA4841-1/ADA4841-2 4.5 VS = 5V G = +1 TIME = 200ns/DIV VIN 5 VOUT 3.5 +125°C OUTPUT VOLTAGE (V) 4 3 2 1 2.5 –40°C 2.0 1.5 0 2.0 1.5 VOUT 2 1 05614-023 –1 VOUT 0.5 0 0 –0.5 –1.0 –1.0 –1.5 –1.5 –2.0 –2.0 Figure 28. Settling Time 6 VS = ±5V VOUT = 2V p-p TIME = 100ns/DIV 1.2 POWER DOWN PIN +25°C 5 POWER DOWN PIN (V) G = +2 0.5 G = +1 0 –0.5 05614-022 –1.0 –1.5 0.5 –0.5 Figure 25. Output Overdrive Recovery 1.0 VOUT (EXPANDED) VIN 1.0 4 0.8 –40°C +125°C 3 0.6 2 0.4 1 0.2 0 –1 VS = 5V G = +1 VIN = 1VDC TIME = 200ns/DIV Figure 29. Power-Up Time vs. Temperature Figure 26. Large Signal Transient Response for Various Gains Rev. C | Page 10 of 20 0 –0.2 VOUT (V) 0 1.5 VIN AND V OUT (V) EXPANDED V OUT (mV) 3 2.0 1.0 1.0 4 1.5 VS = 5V G = +1 VOUT = 2V p-p TIME = 100ns/DIV 05614-041 VS = 5V G = +2 TIME = 100ns/DIV VIN ⋅ 2 5 Figure 27. Slew Rate vs. Temperature 05614-039 6 05614-016 0.5 Figure 24. Input Overdrive Recovery INPUT AND OUTPUT VOLTAGE (V) +25°C 3.0 1.0 0 –1 OUTPUT VOLTAGE (V) G = +2 VS = 5 TIME = 100ns/DIV 4.0 05614-019 INPUT AND OUTPUT VOLTAGE (V) 6 ADA4841-1/ADA4841-2 0.8 3 0.6 +125°C 2 +25°C 0.4 1 –40°C 0.2 0 POWER DOWN PIN 05614-040 0 –1 POWER SUPPLY REJECTION (dB) 4 0 VOUT (V) POWER DOWN PIN 5 –0.2 VS = 5V –20 –40 +PSR –60 –80 –PSR –100 –120 100 1k 10k 100k 1M 10M 100M 10M 100M FREQUENCY (Hz) Figure 30. POWER DOWN Time vs. Temperature Figure 33. PSR vs. Frequency 100 +125°C SUPPLY CURRENT/AMPLIFIER (mA) 1.4 1.2 +25°C 1.0 0.8 –40°C 0.6 0.4 0.2 –0.2 05614-020 0 0.5 0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 VS = 5V 10 1 0.1 0.01 05614-024 VS = 5V CLOSED-LOOP OUTPUT IMPEDANCE (Ω) 1.6 0.001 100 5.0 1k 10k 1M Figure 34. Output Impedance vs. Frequency Figure 31. Supply Current per Amplifier vs. POWER DOWN Pin Voltage 0 100k FREQUENCY (Hz) POWER DOWN PIN (V) 40 VS = ±5V G = +1 30 INPUT OFFSET VOLTAGE (μV) –20 –40 –60 –80 VS = +5V 20 10 0 VS = ±5V –10 –20 VS = +3V –30 –100 1k 10k 100k 1M 10M 100M –40 –50 –40 05614-057 –120 100 05614-009 COMMON-MODE REJECTION (dB) POWER DOWN PIN (V) 1.2 VS = 5V G = +1 VIN = 1VDC 1.0 TIME = 10μs/DIV 05614-025 6 –25 –10 5 20 35 50 65 80 95 110 125 TEMPERATURE (°C) FREQUENCY (Hz) Figure 32. CMR vs. Frequency Figure 35. Input Offset Voltage vs. Temperature for Various Supplies Rev. C | Page 11 of 20 3.6 –40 3.5 G = +1 –50 V = 5V S RL = 1kΩ –60 VS = +5V CROSSTALK (dB) 3.4 VS = +3V 3.3 VS = ±5V –70 –80 –90 –110 3.2 05614-058 –25 –10 5 20 35 50 65 80 95 110 125 TEMPERATURE (°C) –130 –140 10k 1.6 1.5 1.4 1.3 1.2 VS = ±5V 1.0 VS = +5V 05614-059 0.9 VS = +3V 0.8 –40 –25 –10 5 20 35 50 65 80 95 110 100k 1M 10M FREQUENCY (Hz) Figure 38. Crosstalk Output to Output Figure 36. Input Bias Current vs. Temperature for Various Supplies SUPPLY CURRENT (mA) B TO A –120 3.1 –40 1.1 A TO B –100 05614-062 INPUT BIAS CURRENT (μA) ADA4841-1/ADA4841-2 125 TEMPERATURE (°C) Figure 37. Supply Current vs. Temperature for Various Supplies Rev. C | Page 12 of 20 100M 1G ADA4841-1/ADA4841-2 THEORY OF OPERATION AMPLIFIER DESCRIPTION The ADA4841-1/ADA4841-2 are low power, low noise, precision voltage-feedback op amps for single or dual voltage supply operation. The ADA4841-1/ADA4841-2 are fabricated on ADI’s second generation XFCB process and feature trimmed supply current and offset voltage. The 2.1 nV/√Hz voltage noise (very low for a 1.1 mA supply current amplifier), 40 μV offset voltage, and sub 1 μV/°C offset drift is accomplished with an input stage made of an undegenerated PNP input pair driving a symmetrical folded cascode. A rail-to-rail output stage provides the maximum linear signal range possible on low voltage supplies and has the current drive capability needed for the relatively low resistance feedback networks required for low noise operation. CMRR, PSRR, and open-loop gain are all typically above 100 dB, preserving the precision performance in a variety of configurations. Gain bandwidth is kept high for this power level to preserve the outstanding linearity performance for frequencies up to 100 kHz. The ADA4841-1 has a powerdown function to further reduce power consumption. All this results in a low noise, power efficient, precision amplifier that is well-suited for high resolution and precision applications. Figure 39 shows a typical connection diagram and the major dc error sources. The ideal transfer function (all error sources set to 0 and infinite dc gain) can be written as VCM VP − VPNOM VOUT ⎞ ⎛ RF ⎛ + + ⎜ VOFFSETNOM + ⎟ × ⎜1 + CMRR PSRR A ⎠ ⎜⎝ RG ⎝ ⎞ ⎟ × VIP ⎟ ⎠ ⎛R − ⎜⎜ F ⎝ RG ⎞ ⎟ × VIN ⎟ ⎠ (1) RF where: VOFFSETNOM is the offset voltage at the specified supply voltage. This is measured with the input and output at midsupply. VCM is the common-mode voltage. VP is the power supply voltage. VpNOM is the specified power supply voltage. CMRR is the common-mode rejection ratio. PSRR is the power supply rejection ratio. The output error due to the input currents can be estimated as ⎛ R VOUTERROR = (RF || RG ) × ⎜⎜1 + F ⎝ RG ⎞ ⎛ R ⎟ I B − − RS × ⎜ 1 + F ⎟ ⎜ R G ⎠ ⎝ ⎞ ⎟ × I B+ ⎟ ⎠ Note that setting RS equal to RF||RG compensates for the voltage error due to the input bias current. Figure 40 illustrates the primary noise contributors for the typical gain configurations. The total rms output noise is the root-mean-square of all the contributions. + VOUT – RS RF 05614-004 IB+ vn _ RG = 4kT × RG Figure 39. Typical Connection Diagram and DC Error Sources vn _ RF = 4kT × RF ven RG ien This reduces to the familiar forms for inverting and noninverting op amp gain expressions ⎛ R = ⎜⎜1 + F ⎝ RG ⎞ ⎟ ×VIP ⎟ ⎠ vn _ RS = 4kT × RS (2) ⎞ ⎟ ×VIN ⎟ ⎠ (3) (Inverting gain, VIP = 0 V) Rev. C | Page 13 of 20 + vout_en – RS ien (Noninverting gain, VIN = 0 V) ⎛ − RF VOUT = ⎜⎜ ⎝ RG (5) NOISE CONSIDERATIONS + VOS – RG IB– VOUT ⎞ (4) ⎟ ⎟ ⎠ Figure 40. Noise Sources in Typical Connection 05614-005 ⎛ R VOUT = ⎜⎜1 + F ⎝ RG – VIP + VOUTERROR = A is the dc open-loop gain. DC ERRORS – VIN + The total output voltage error is the sum of errors due to the amplifier offset voltage and input currents. The output error due to the offset voltage can be estimated as ADA4841-1/ADA4841-2 The output noise spectral density can be calculated by vout _ en = [ ] 2 (6) where: k is Boltzmann’s Constant. T is the absolute temperature, degrees Kelvin. 300 260 ien is the amplifier input current noise spectral density, pA/√Hz. RS is the source resistance as shown in Figure 40. RF and RG are the feedback network resistances, as shown in Figure 40. 1000 100 140 AMPLIFIER + RESISTOR NOISE 10 20 100 1k –60 –100 –140 –180 –220 –260 –300 3.00 3.20 3.40 3.60 3.80 4.00 4.20 4.40 4.60 4.80 5.00 COMMON-MODE VOLTAGE (V) Figure 42. +CMV vs. Common-Mode Error vs. VOS 0 –50 –100 –150 –40°C –200 –250 –300 +25°C –350 –400 –450 +125°C –500 –550 –600 –650 –700 –750 –800 –6.00 –5.80 –5.60 –5.40 –5.20 –5.00 –4.80 –4.60 –4.40 –4.20 –4.00 05614-007 10k –40°C –20 1 0.1 10 +25°C 60 TOTAL AMPLIFIER NOISE SOURCE RESISTANCE NOISE +125°C 100 05614-054 NOISE (nV/ Hz) 180 COMMON-MODE ERROR (μV) Source resistance noise, amplifier voltage noise (ven), and the voltage noise from the amplifier current noise (ien × RS) are all subject to the noise gain term (1 + RF/RG). Note that with a 2.1 nV/√Hz input voltage noise and 1.4 pA/√Hz input current, the noise contributions of the amplifier are relatively small for source resistances between approximately 200 Ω and 30 kΩ. Figure 41 shows the total RTI noise due to the amplifier vs. the source resistance. In addition, the value of the feedback resistors used impacts the noise. It is recommended to keep the value of feedback resistors between 250 Ω and 1 kΩ to keep the total noise low. COMMON-MODE ERROR (μV) ven is the amplifier input voltage spectral density, nV/√Hz. 220 05614-055 2 ⎛ R ⎞ ⎛R ⎞ 2 2 4 kTRf + ⎜⎜1 + F ⎟⎟ 4 kTRs + ien RS 2 + ven + ⎜⎜ F ⎟⎟ 4 kTRg + ien 2 R F 2 R G ⎠ ⎝ ⎝ RG ⎠ The input stage positive limit is almost exactly a volt below the positive supply at room temperature. Input voltages above that start to show clipping behavior. The positive input voltage limit increases with temperature with a coefficient of about 2 mV/°C. The lower supply limit is nominally below the minus supply; therefore, in a standard gain configuration, the output stage limits the signal headroom on the negative supply side. Figure 42 and Figure 43 show the nominal CMRR behavior at the limits of the input headroom for three temperatures—this is generated using the subtractor topology shown in Figure 44, which avoids the output stage limitation. COMMON-MODE VOLTAGE (V) Figure 43. −CMV vs. Common-Mode Error vs. VOS 100k – VCM + SOURCE RESISTANCE (Ω) + VOUT – 05614-051 Figure 41. RTI Noise vs. Source Resistance HEADROOM CONSIDERATIONS The ADA4841-1/ADA4841-2 are designed to provide maximum input and output signal ranges with 16-bit to 18-bit dc linearity. As the input or output headroom limits are reached, the signal linearity degrades. Rev. C | Page 14 of 20 Figure 44. Common-Range Subtractor ADA4841-1/ADA4841-2 60 Figure 45 shows the amplifier frequency response as a G = −1 inverter with the input and output stage biased near the negative supply rail. VS– = –150mV VS– = –100mV VS– = –200mV VS– = –50mV 30 20 VS– = –20mV –3 10 G = +2 G = +5 –6 0 10 100 10000 1000 CAPACITANCE LOAD (pF) 05614-017 –9 –12 0.1 05614-050 GAIN (dB) 0 40 1 10 100 FREQUENCY (MHz) Figure 45. Small Signal Frequency Response vs. Negative Supply Bias The input voltage (VIN) and reference voltage (VIP) are both at 0 V, (see Figure 39). +VS is biased at +5 V, and −VS is swept from −200 mV to −20 mV. With the input and output voltages biased 200 mV above the bottom rail, the G = −1 inverter frequency response is not much different from what is seen with the input and output voltages biased near midsupply. At 150 mV bias, the frequency response starts to decrease and at 20 mV, the inverter bandwidth is less than half its nominal value. Figure 46. Series Resistance vs. Capacitance Load INPUT PROTECTION The ADA4841-1/ADA4841-2 are fully protected from ESD events, withstanding human body model ESD events of 2.5 keV and charge device model events of 1 keV with no measured performance degradation. The precision input is protected with an ESD network between the power supplies and diode clamps across the input device pair, as shown in Figure 47. VCC BIAS ESD VP CAPACITANCE DRIVE A small resistor in series with the amplifier output and the capacitive load mitigates the problem. Figure 46 plots the recommended series resistance vs. capacitance for gains of +1, +2, and +5. VN ESD Capacitance at the output of an amplifier creates a delay within the feedback path that, if within the bandwidth of the loop, can create excessive ringing and oscillation. The G = +1 follower topology has the highest loop bandwidth of any typical configuration and, therefore, is the most vulnerable to the effects of capacitance load. ESD ESD VEE TO REST OF AMPLIFIER 05614-006 3 VS+ = 5V G = –1 VIN = 20mV p-p SERIES RESISTANCE (Ω) 6 G = +1 50 Figure 47. Input Stage and Protection Diodes For differential voltages above approximately 1.4 V, the diode clamps start to conduct. Too much current can cause damage due to excessive heating. If large differential voltages need to be sustained across the input terminals, it is recommended that the current through the input clamps be limited to below 150 mA. Series input resistors sized appropriately for the expected differential overvoltage provide the needed protection. The ESD clamps start to conduct for input voltages more than 0.7 V above the positive supply and input voltages more than 0.7 V below the negative supply. It is recommended that the fault current be limited to less than 150 mA if an overvoltage condition is expected. Rev. C | Page 15 of 20 ADA4841-1/ADA4841-2 POWER-DOWN OPERATION Figure 48 shows the ADA4841-1 power-down circuitry. If the POWER DOWN pin is left unconnected, then the base of the input PNP transistor is pulled high through the internal pull-up resistor to the positive supply, and the part is turned on. Pulling the POWER DOWN pin approximately 1.7 V below the positive supply turns the part off, reducing the supply current to approximately 40 μA. VCC IBIAS ESD POWER DOWN ESD VEE 05614-052 TO AMPLIFIER BIAS Figure 48. POWER DOWN Circuit The POWER DOWN pin is protected with ESD clamps, as shown in Figure 48. Voltages beyond the power supplies cause these diodes to conduct. The guidelines for limiting the overload current in the input protection section should also be followed for the POWER DOWN pin. Rev. C | Page 16 of 20 ADA4841-1/ADA4841-2 APPLICATIONS TYPICAL PERFORMANCE VALUES RECONSTRUCTION FILTER To reduce design time and eliminate uncertainty Table 6 provides a convenient reference for typical gains, component values, and performance parameters. The ADA4841-1/ADA4841-2 can also be used as a reconstruction filter at the output of DACs for suppression of the sampling frequency. The filter shown in Figure 50 is a two-pole, 500 kHz Sallen-Key LPF with a fixed gain of G = +1.6. 16-BIT ADC DRIVER C2 1320pF The combination of low noise, low power, and high speed make the ADA4841-1/ADA4841-2 the perfect driver solution for low power, 16-bit ADCs, such as the AD7685. Figure 49 shows a typical 16-bit single-supply application. +5V Rail-to-rail input amplifiers are usually higher noise than the ADA4841-1/ADA4841-2 and cannot be used in this mode because of the nonlinear region around the crossover point of their input stages. The ADA4841-1/ADA4841-2, which have no crossover region but have a wide linear input range from 100 mV below ground to 1 V below positive rail, solve this problem, as shown in Figure 49. The amplifier, when configured as a follower, has a linear signal range from 0.25 V above the minus supply voltage (limited by the amplifier’s output stage) to 1 V below the positive supply (limited by the amplifier input stage). A 0 V to +4.096 V signal range can be accommodated with a positive supply as low as +5.2 V and a negative power supply of −0.25 V. The 5.2 V supply also allows the use of a small, low dropout, low temperature drift ADR364 reference voltage. If ground is used as the amplifier negative supply, then note that at the low end of the input range close to ground, the ADA4841-1/ ADA4841-2 exhibit substantial nonlinearity, as any rail-to-rail output amplifier. The ADA4841-1/ADA4841-2 drive a onepole, low-pass filter. This filter limits the already very low noise contribution from the amplifier to the AD7685. INPUT 0.1μF R2 249Ω C1 1320pF U1 OUTPUT 0.1μF 10μF –5V R3 840Ω R4 499Ω Figure 50. Two-Pole 500 kHz Reconstruction Filter Schematic Setting the resistors and capacitors equal to each other greatly simplifies the design equations for the Sallen-Key filter. The corner frequency, or −3 dB frequency, can be described by the equation fC = 1 2πR1C1 The quality factor, or Q, is shown in the equation Q= 1 3−K For minimum peaking, set Q equal to 0.707. The gain, or K, of the amplifier is K= R4 +1 R3 +5.2V 100nF ADA4841 Resistor values are kept low for minimal noise contribution, offset voltage, and optimal frequency response. 100nF ADR364 10μF 100nF 0V TO 4.096V 33Ω REF VDD IN+ AD7685 2.7nF –0.25V IN– VIO SDI SCK SDO CNV 05614-060 GND 05614-044 There are different challenges to a single-supply, high resolution design, and the ADA4841-1/ADA4841-2 address these nicely. In a single-supply system, a main challenge is using the amplifier in buffer mode with the lowest output noise and preserving linearity compatible with the ADC. R1 249Ω 10μF Figure 49. ADC Driver Schematic Rev. C | Page 17 of 20 ADA4841-1/ADA4841-2 Table 6. Recommended Values and Typical Performance Gain +1 +2 −1 +5 +10 +20 RF (Ω) 0 499 499 499 499 499 RG (Ω) N/A 499 499 124 54.9 26.1 −3 dB BW (MHz) 77 34 38 11 5 2.3 Slew Rate (V/μs) 12.5 12.5 12.5 12 12 11.2 Capacitor selection is critical for optimal filter performance. Capacitors with low temperature coefficients, such as NPO ceramic capacitors, are good choices for filter elements. Figure 51 shows the filter response. 5 0 –5 GAIN (dB) –10 –15 –20 –25 Peaking (dB) 0.9 0.3 0.4 0 0 0 Output Noise ADA4841-1/ ADA4841-2 Only (nV/√Hz) 2 4 4 10 20 40 Total Output Noise Including Resistors (nV/√Hz) 2 5.73 5.73 11.9 21.1 42.2 POWER SUPPLY BYPASSING Power supply bypassing is a critical aspect in the performance of the ADA4841-1/ADA4841-2. A parallel connection of capacitors from each of the power supply pins to ground works best. A typical connection is shown in Figure 50. Smaller value capacitors offer better high frequency response where larger value electrolytics offer better low frequency performance. Paralleling different values and sizes of capacitors helps to ensure that the power supply pins are provided a low ac impedance across a wide band of frequencies. This is important for minimizing the coupling of noise into the amplifier. This can be especially important when the amplifier PSR is starting to roll off—the bypass capacitors can help lessen the degradation in PSR performance. –30 –40 0.03 05614-043 –35 0.1 1 FREQUENCY (MHz) 10 Figure 51. Filter Frequency Response LAYOUT CONSIDERATIONS To ensure optimal performance, careful and deliberate attention must be paid to the board layout, signal routing, power supply bypassing, and grounding. GROUND PLANE It is important to avoid ground in the areas under and around the input and output of the ADA4841-1/ADA4841-2. Stray capacitance created between the ground plane and the input and output pads of a device are detrimental to high speed amplifier performance. Stray capacitance at the inverting input, along with the amplifier input capacitance, lowers the phase margin and can cause instability. Stray capacitance at the output creates a pole in the feedback loop. This can reduce phase margin and can cause the circuit to become unstable. Starting directly at the ADA4841-1/ADA4841-2 power supply pins, the smallest value capacitor should be placed on the same side of the board as the amplifier, and as close as possible to the amplifier power supply pin. The ground end of the capacitor should be connected directly to the ground plane. Keeping the capacitors’ distance short but equal from the load is important and can improve distortion performance. This process should be repeated for the next largest value capacitor. It is recommended that a 0.1 μF ceramic 0508 case be used. The 0508 case size offers low series inductance and excellent high frequency performance. A 10 μF electrolytic capacitor should be placed in parallel with the 0.1 μF capacitor. Depending on the circuit parameters, some enhancement to performance can be realized by adding additional capacitors. Each circuit is different and should be individually analyzed for optimal performance. Rev. C | Page 18 of 20 ADA4841-1/ADA4841-2 OUTLINE DIMENSIONS 2.90 BSC 5.00 (0.1968) 4.80 (0.1890) 8 5 4.00 (0.1574) 3.80 (0.1497) 1 6 5 4 1 2 3 2.80 BSC 1.60 BSC 6.20 (0.2440) 4 5.80 (0.2284) PIN 1 INDICATOR 1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0040) 0.51 (0.0201) COPLANARITY SEATING 0.31 (0.0122) 0.10 PLANE 0.95 BSC 0.50 (0.0196) × 45° 0.25 (0.0099) 1.75 (0.0688) 1.35 (0.0532) 1.30 1.15 0.90 8° 0.25 (0.0098) 0° 1.27 (0.0500) 0.40 (0.0157) 0.17 (0.0067) 1.45 MAX COMPLIANT TO JEDEC STANDARDS MS-012-AA 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. 0.15 MAX Figure 52. 8-Lead Standard Small Outline Package [SOIC_N] Narrow Body (R-8) Dimensions shown in millimeters and (inches) 8 1 5 5.15 4.90 4.65 4 PIN 1 0.65 BSC 0.95 0.85 0.75 1.10 MAX 0.15 0.00 0.38 0.22 COPLANARITY 0.10 0.23 0.08 8° 0° 0.50 0.30 SEATING PLANE 0.22 0.08 10° 4° 0° 0.60 0.45 0.30 COMPLIANT TO JEDEC STANDARDS MO-178-AB Figure 54. 6-Lead Small Outline Transistor Package [SOT-23] (RJ-6) Dimensions shown in millimeters 3.20 3.00 2.80 3.20 3.00 2.80 1.90 BSC 0.80 0.60 0.40 SEATING PLANE COMPLIANT TO JEDEC STANDARDS MO-187-AA Figure 53. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters Rev. C | Page 19 of 20 ADA4841-1/ADA4841-2 ORDERING GUIDE Model ADA4841-1YRZ 1 ADA4841-1YRZ-R71 ADA4841-1YRZ-RL1 ADA4841-1YRJZ-R21 ADA4841-1YRJZ-R71 ADA4841-1YRJZ-RL1 ADA4841-2YRMZ1 ADA4841-2YRMZ-R71 ADA4841-2YRMZ-RL1 ADA4841-2YRZ1 ADA4841-2YRZ-R71 ADA4841-2YRZ-RL1 1 Temperature Range −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C −40°C to +125°C Package Description 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 6-Lead SOT-23 6-Lead SOT-23 6-Lead SOT-23 8-Lead MSOP 8-Lead MSOP 8-Lead MSOP 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N Z = Pb-free part. ©2006 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D05614–0–3/06(C) Rev. C | Page 20 of 20 Package Option R-8 R-8 R-8 RJ-6 RJ-6 RJ-6 RM-8 RM-8 RM-8 R-8 R-8 R-8 Ordering Quantity 1 1,000 2,500 250 3,000 10,000 1 1,000 3,000 1 1,000 2,500 Branding HQB HQB HQB HRB HRB HRB