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Low Power, Low Noise and Distortion, Rail-to-Rail Output Amplifier ADA4841-1/ADA4841-2
FEATURES
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/s slew rate 175 ns settling time to 0.1% Low offset voltage 0.3 mV max Rail-to-rail output Power down Wide supply range: 2.7 V to 12 V
CONNECTION DIAGRAMS
ADA4841-1
TOP VIEW NC 1 (Not to Scale) 8 POWER DOWN -IN 2 +IN 3 -VS 4 7 +VS
05614-001
6 VOUT 5 NC
Figure 1. 8-Lead SOIC (R)
ADA4841-2
OUT1 1 -IN1 2 +IN1 3 -VS 4 TOP VIEW (Not to Scale)
8 7 6 5
+VS OUT2 -IN2 +IN2
05614-064
Figure 2. 8-Lead MSOP (RM-8)
APPLICATIONS
Low power, low noise signal processing Battery-powered instrumentation 16-bit PulSAR(R) ADC drivers
GENERAL DESCRIPTION
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. The ADA4841-1/ADA4841-2 output can swing to less than 100 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 20 pF of capacitive load with minimal peaking. 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.
Rev. B
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.
The ADA4841-1/ADA4841-2 packages feature Pb-free lead finish. The amplifiers are rated to work over the industrial temperature range (-40C to +125C).
-30 -40 VS = 5V G = +1
HARMONIC DISTORTION (dBc)
-50 -60 -70 2V p-p THIRD -80 -90 -100 -110 -120 0.01 2V p-p SECOND
05614-048
0.1 FREQUENCY (MHz)
1
Figure 3. Harmonic Distortion
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 (c) 2005 Analog Devices, Inc. All rights reserved.
ADA4841-1/ADA4841-2 TABLE OF CONTENTS
Features .............................................................................................. 1 Applications....................................................................................... 1 Connection Diagrams...................................................................... 1 General Description ......................................................................... 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Absolute Maximum Ratings............................................................ 6 Thermal Resistance ...................................................................... 6 ESD Caution.................................................................................. 6 Typical Performance Characteristics ............................................. 7 Theory of Operation ...................................................................... 13 Amplifier Description................................................................ 13 DC Errors .................................................................................... 13 Noise Considerations ................................................................. 13 Headroom Considerations........................................................ 14 Capacitance Drive ...................................................................... 15 Input Protection ......................................................................... 15 Power-Down Operation ............................................................ 16 Applications..................................................................................... 17 Typical Performance Values...................................................... 17 16-Bit ADC Driver..................................................................... 17 Reconstruction Filter ................................................................. 17 Layout Considerations............................................................... 18 Ground Plane.............................................................................. 18 Power Supply Bypassing ............................................................ 18 Outline Dimensions ....................................................................... 19 Ordering Guide .......................................................................... 20
REVISION HISTORY
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. B | Page 2 of 20
ADA4841-1/ADA4841-2 SPECIFICATIONS
TA = 25C, VS = 5 V, RL = 1 k, 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 VO = 0.02 V p-p VO = 2 V p-p G = +1, VO = 9 V step, RL = 1 k G = +1, VO = 8 V step G = +1, VO = 8 V step fC = 100 kHz, VO = 2 V p-p, G = +1 fC = 1 MHz, VO = 2 V p-p f = 100 kHz f = 100 kHz Min 58 12 Typ 80 3 13 650 1000 -111/-105 -80/-67 2.1 1.4 40 1 3 0.1 120 90 25 1 3 VCM = -2 V to +2 V -5.1 95 +4 115 70 60 Enabled Power down POWER DOWN = +5 V POWER DOWN = -5 V >3.6 <3.2 1 -13 1 40 G > +1 Sourcing, VIN = +VS , RL = 50 to GND Sinking, VIN = -VS , RL = 50 to GND 30% overshoot 4.90 4.955 30 60 15 12 1.5 90 2 -30 300 5.3 0.4 Max Unit MHz MHz V/s ns ns dBc dBc nV/Hz pA/Hz V V/C A A dB M k pF pF V dB V nA V V A A s s V mA mA pF V mA A dB dB
VO = 4 V
103
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 1.2 40 110 120
95 96
Rev. B | Page 3 of 20
ADA4841-1/ADA4841-2
TA = 25C, VS = 5 V, RL = 1 k, 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 VO = 0.02 V p-p VO = 2 V p-p G = +1, VO = 4 V step, RL = 1 k G = +1, VO = 2 V step G = +1, VO = 2 V step 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 Min 54 10 Typ 80 3 12 175 550 -109/-105 -78/-66 2.1 1.4 -117 40 1 3 0.1 124 90 25 1 3 VCM = 2.5 V to 4 V -0.1 88 +4 115 70 70 Enabled Power down POWER DOWN = 5 V POWER DOWN = 0 V >3.6 <3.2 1 -13 1 40 G > +1 Sourcing, VIN = +VS, RL = 50 to VCM Sinking, VIN = -VS, RL = 50 to VCM 30% overshoot 0.065 to 4.920 0.029 to 4.974 30 60 15 12 1.4 70 2 -30 300 5.3 0.4 Max Unit MHz MHz V/s ns ns dBc dBc nV/Hz pA/Hz dB V V/C A A dB M k pF pF V dB V nA
VO = 0.5 V to 4.5 V
103
V A A s s V mA mA pF V mA A dB dB
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 1.1 35 110 120
95 96
Rev. B | Page 4 of 20
ADA4841-1/ADA4841-2
TA = 25C, VS = 3 V, RL = 1 k, 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 VO = 0.02 V p-p G = +1, VO = 2 V step, RL = 1 k G = +1, VO = 1 V step G = +1, VO = 1 V step fC = 100 kHz, VO = 1 V p-p fC = 1 MHz, VO = 1 V p-p f = 100 kHz f = 100 kHz Min 52 10 Typ 80 12 120 250 -97/-100 -79/-80 2.1 1.4 40 1 3 0.1 123 90 25 1 3 VCM = 1.5 V to 1.9 V -0.1 86 +2 115 70 60 Enabled Power down POWER DOWN = 3 V POWER DOWN = 0 V >1.6 <1.2 1 -10 1 40 G > +1 Sourcing, VIN = +VS, RL = 50 to VCM Sinking, VIN = -VS, RL = 50 to VCM 30% overshoot 0.045 to 2.955 0.023 to 2.988 30 60 30 12 1.3 60 2 -30 300 5.3 0.4 Max Unit MHz V/s ns ns dBc dBc nV/Hz pA/Hz V V/C A A dB M k pF pF V dB V nA
VO = 0.5 V to 2.5 V
101
V A A s s V mA mA pF V mA A dB dB
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 1.1 25 110 120
95 96
Rev. B | Page 5 of 20
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 Rating 12.6 V See Figure 4 -VS - 0.5 V to +VS + 0.5 V 1.8 V -65C to +125C -40C to +85C JEDEC J-STD-20 150C
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). PD = Quiescent Power + (Total Drive Power - Load Power)
V V PD = (VS x I S ) + S x OUT 2 RL
VOUT 2 R L
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.
RMS output voltages should be considered. If RL is referenced to -VS, as in single-supply operation, the total drive power is VS x IOUT. If the rms signal levels are indeterminate, consider the worst case, when VOUT = VS/4 for RL to midsupply.
PD = (VS x I S ) +
(VS /4 )2
RL
THERMAL RESISTANCE
JA is specified for the worst-case conditions, that is, JA is specified for device soldered in circuit board for surface-mount packages. Table 5. Thermal Resistance
Package Type 8-lead SOIC 8-lead MSOP JA 125 130 Unit C/W C/W
In single-supply operation with RL referenced to -VS, worst case is VOUT = VS/2. Airflow increases heat dissipation, effectively reducing JA. In addition, more metal directly in contact with the package leads and through holes under the device reduces JA. Figure 4 shows the maximum safe power dissipation in the package vs. the ambient temperature for the 8-lead MSOP (145C/W) and the 8-lead SOIC (125C/W) on a JEDEC standard 4-layer board. JA values are approximations.
2.0
Maximum Power Dissipation
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 150C, 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 150C for an extended period can result in changes in silicon devices, potentially causing degradation or loss of functionality.
MAXIMUM POWER DISSIPATION (W)
SOIC 1.5 MSOP 1.0
0.5
05614-061
0
-55
-35
-15
5
25
45
65
85
105
125
AMBIENT TEMPERATURE (C)
Figure 4. 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. B | Page 6 of 20
ADA4841-1/ADA4841-2 TYPICAL PERFORMANCE CHARACTERISTICS
RL = 1 k, unless otherwise noted.
3 VOUT = 2V pp VS = 5V 3 G = +1 VS = 5V VIN = 20mV p-p G = +1 -40C +25C
NORMALIZED CLOSED-LOOP GAIN (dB)
0 0 -3 G = +10 G = +2 -6
GAIN (dB)
+125C -3
-6 -9
05614-021 05614-028
-12 0.1
1 FREQUENCY (MHz)
10
-9 0.1
1
10 FREQUENCY (MHz)
100
Figure 5. Large Signal Frequency Response vs. Gain
6 VIN = 20mV p-p G = +1 VS = 5V 20pF 20pF WITH 100 SNUBBER
Figure 8. Small Signal Frequency Response vs. Temperature
2 1 0 VIN = 20mV p-p G = +1 VS = +5V
VS = +3V
VS = 5V
3
CLOSED-LOOP GAIN (dB)
GAIN (dB)
05614-026
0 0pF -3
-1 -2 -3 -4
05614-029
10pF
-6
-5 -6 0.1
-9 0.1
1
10 FREQUENCY (MHz)
100
1
10 FREQUENCY (MHz)
100
Figure 6. Small Signal Frequency Response vs. Capacitive Load
3 VIN = 20mV p-p VS = 5V G = -1
Figure 9. Small Signal Frequency Response vs. Supply Voltage
3 VS = 5V G = +1
NORMALIZED CLOSED-LOOP GAIN (dB)
G = +1
10mV p-p
0 G = +10 -3
0
GAIN (dB)
-3
2V p-p
400mV p-p 20mV p-p
-6
-6
-9
05614-027
100mV p-p
05614-014
-12 0.1
1
10 FREQUENCY (MHz)
100
-9 0.1
1
10 FREQUENCY (MHz)
100
Figure 7. Small Signal Frequency Response vs. Gain
Figure 10. Frequency Response for Various VOUT
Rev. B | Page 7 of 20
ADA4841-1/ADA4841-2
140 120 100 80 60 40 20 0 -20 10 PHASE MAGNITUDE VS = 5V 0 -20
-30 -40
OPEN-LOOP PHASE (Degrees)
VOUT = 2V p-p G = +2 +5V SECOND
OPEN-LOOP GAIN (dB)
-40 -60 -80 -100 -120 -140 -160 100M
HARMONIC DISTORTION (dBc)
-50 -60 -70 -80 -90 -100 -110 -120 -130 0.01 5V SECOND 0.1 +3V THIRD +3V SECOND
5V THIRD
05614-047
+5V THIRD
100
1k
10k
100k
1M
10M
05614-042
FREQUENCY (Hz)
1
FREQUENCY (MHz)
Figure 11. Open-Loop Gain and Phase vs. Frequency
-30 -40
Figure 14. Harmonic Distortion vs. Frequency for Various Supplies
10 VS = 5V
VS = + 5V VOUT = 2V p-p
HARMONIC DISTORTION (dBc)
-50 -60 -70 -80 -90 -100 -110 -120 -130 0.01 0.1 FREQUENCY (MHz) G = +2 SECOND G = +5 SECOND
G = +1 SECOND G = +1 THIRD
05614-045
VOLTAGE NOISE (nV/ Hz)
G = +5 THIRD
G = +2 THIRD 1
1 10
100
1k
10k
100k
1M
10M
FREQUENCY (Hz)
Figure 12. Harmonic Distortion vs. Frequency for Various Gains
-30 -40
Figure 15. Voltage Noise vs. Frequency
100 VS = 5V
VS = 5V G = +1 8V p-p SECOND
HARMONIC DISTORTION (dBc)
-50 8V p-p THIRD -60 -70 -80 -90 -100
05614-046
CURRENT NOISE (pA/ Hz)
10
4V p-p THIRD 4V p-p SECOND
1
-120 0.01
2V p-p SECOND 0.1 FREQUENCY (MHz) 1
0.1 10
100
1k
10k
100k
1M
FREQUENCY (Hz)
Figure 13. Harmonic Distortion vs. Frequency for Various Output Voltages
Figure 16. Current Noise vs. Frequency
Rev. B | Page 8 of 20
05614-018
-110
2V p-p THIRD
05614-034
ADA4841-1/ADA4841-2
55 COUNT = 190 50 x = 0.36V/C = 1.21V/C 45
OUTPUT VOLTAGE (V)
0.25 G = +2 TIME = 50ns/DIV VS = +5V 0.23 VS = 5V 0.22 VS = +3V
0.24
NUMBER OF PARTS
40 35 30 25 20 15 10 5 0 -5 -4 -2 0 2 4 6
05614-053
0.21
0.20
05614-033
0.19
OFFSET DRIFT DISTRIBUTION (V/C)
Figure 17. Input Offset Voltage Drift Distribution
10 9 8 G = +1 VS = 5V
Figure 20. Small Signal Transient Response for Various Supplies
0.15 G = +2 VIN = 20mV p-p TIME = 50ns/DIV 0pF 0.13
0.14
OUTPUT VOLTAGE (V)
NONLINEARITY (V)
7 6 5 4 3 2
10pF
0.12
0.11
0
0
1
2 VIN (V)
3
4
5
0.09
Figure 18. Nonlinearity vs. VIN
100 80 60
VOFFSET (V)
Figure 21. Small Signal Transient Response for Various Capacitive Loads
0.130 0.125 0.120
VS = 5
G = +1 TIME = 50ns/DIV
VS = 3V
OUTPUT VOLTAGE (V)
40 20 0 -20
05614-036
0.115 0.110 0.105 0.100
VS = 5V
-60 -6
0.090
-4
-2
0 VOUT (V)
2
4
6
Figure 19. Input Error Voltage vs. Output Voltage
Figure 22. Small Signal Transient Response for Various Supplies
Rev. B | Page 9 of 20
05614-030
-40
0.095
05614-031
1
05614-013
0.10
20pF 47pF
ADA4841-1/ADA4841-2
6 5 VOUT 4 3 2 1 0 -1 VIN VS = 5V G = +1 TIME = 200ns/DIV
4.5 4.0 3.5 G = +2 VS = 5 TIME = 100ns/DIV +125C 3.0 2.5 -40C 2.0 1.5 1.0
05614-019
INPUT AND OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
+25C
0
Figure 23. Input Overdrive Recovery
Figure 26. Slew Rate vs. Temperature
6 5 4 3 2 1 0 -1
VIN 2 VOUT
VS = 5V G = +2 TIME = 100ns/DIV
2.0 1.5 1.0
INPUT AND OUTPUT VOLTAGE (V)
VS = 5V G = +1 VOUT = 2V p-p TIME = 100ns/DIV VOUT
2.0 1.5 1.0 0.5 0 -0.5 -1.0
05614-041
EXPANDED V OUT (mV)
05614-016
0.5
0.5 0 -0.5 -1.0 VIN
VOUT (EXPANDED)
05614-023
-1.5 -2.0
-1.5 -2.0
Figure 24. Output Overdrive Recovery
6
Figure 27. Settling Time
1.2 POWER DOWN PIN 5 4 -40C 3 2 1 0 -1 VS = 5V G = +1 VIN = 1VDC TIME = 200ns/DIV +125C +25C 1.0 0.8
1.5
1.0
VS = 5V VOUT = 2V p-p TIME = 100ns/DIV
OUTPUT VOLTAGE (V)
0.5 G = +1 0
POWER DOWN PIN (V)
G = +2
0.4 0.2 0 -0.2
-0.5
-1.5
05614-022
Figure 25. Large Signal Transient Response for Various Gains
Figure 28. Power-Up Time vs. Temperature
Rev. B | Page 10 of 20
05614-039
-1.0
VOUT (V)
0.6
VIN AND V OUT (V)
ADA4841-1/ADA4841-2
6 5 4 3 +125C 2 1 0 -1 POWER DOWN PIN +25C -40C 0.4 0.2 0 -0.2 POWER DOWN PIN 1.2 VS = 5V G = +1 VIN = 1VDC 1.0 TIME = 10s/DIV 0.8 VOUT (V) 0.6
0
VS = 5V
POWER SUPPLY REJECTION (dB)
-20
POWER DOWN PIN (V)
-40
+PSR
-60
-80 -PSR -100
05614-025
05614-040
-120 100
1k
10k
100k
1M
10M
100M
FREQUENCY (Hz)
Figure 29. POWER DOWN Time vs. Temperature
1.6 1.4
Figure 32. PSR vs. Frequency
100
VS = 5V
+125C
VS = 5V
CLOSED-LOOP OUTPUT IMPEDANCE ()
SUPPLY CURRENT/AMPLIFIER (mA)
1.2 1.0 0.8 0.6 0.4 0.2
05614-020
10
+25C
1
-40C
0.1
0.01
05614-024
0 -0.2
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0.001 100
1k
10k
100k
1M
10M
100M
POWER DOWN PIN (V)
FREQUENCY (Hz)
Figure 30. Supply Current per Amplifier vs. POWER DOWN Pin Voltage
0 VS = 5V G = +1
Figure 33. Output Impedance vs. Frequency
40 30
INPUT OFFSET VOLTAGE (V)
COMMON-MODE REJECTION (dB)
-20
20 10 0 VS = 5V -10 -20 -30 VS = +3V
VS = +5V
-40
-60
-80
-100
05614-009
-120 100
1k
10k
100k
1M
10M
100M
-50 -40
-25
-10
5
20
35
50
65
80
95
110
125
FREQUENCY (Hz)
TEMPERATURE (C)
Figure 31. CMR vs. Frequency
Figure 34. Input Offset Voltage vs. Temperature for Various Supplies
Rev. B | Page 11 of 20
05614-057
-40
ADA4841-1/ADA4841-2
3.6
-40 G = +1 -50 V = 5V S RL = 1k -60
3.5
INPUT BIAS CURRENT (A)
VS = +5V 3.4
CROSSTALK (dB)
-70 -80 -90 -100 -110 -120 B TO A
05614-062
3.3
VS = +3V VS = 5V
A TO B
3.2
05614-058
-130 -140 10k 100k 1M 10M FREQUENCY (Hz) 100M
3.1 -40
-25
-10
5
20
35
50
65
80
95
110
125
TEMPERATURE (C)
1G
Figure 35. Input Bias Current vs. Temperature for Various Supplies
1.6 1.5 1.4 1.3 1.2 1.1 1.0 VS = +5V VS = +3V 0.8 -40 -25 -10 5 20 35 50 65 80 95 110
05614-059
Figure 37. Crosstalk Output to Output
SUPPLY CURRENT (mA)
VS = 5V
0.9
125
TEMPERATURE (C)
Figure 36. Supply Current vs. Temperature for Various Supplies
Rev. B | Page 12 of 20
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 V offset voltage, and sub 1 V/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.
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
VOUTERROR = VCM VP - VPNOM VOUT RF + + VOFFSETNOM + x 1 + CMRR PSRR A RG 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. A is the dc open-loop gain. The output error due to the input currents can be estimated as R VOUTERROR = (RF || RG ) x 1 + F R G R I B - - RS x 1 + F R G x I B+ (5) (4)
DC ERRORS
Figure 38 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
R VOUT = 1 + F R G
x VIP
R - F R G
RF
x VIN
(1)
Note that setting RS equal to RF||RG compensates for the voltage error due to the input bias current.
- VIN +
RG IB-
+ VOS - + VOUT -
NOISE CONSIDERATIONS
Figure 39 illustrates the primary noise contributors for the typical gain configurations. The total rms output noise is the root-mean-square of all the contributions.
05614-004
- VIP +
RS IB+
RF vn _ RG = 4kT x RG RG ien ven
vn _ RF = 4kT x RF
Figure 38. Typical Connection Diagram and DC Error Sources
+ vout_en -
This reduces to the familiar forms for inverting and noninverting op amp gain expressions
vn _ RS = 4kT x RS
RS ien
05614-005
R VOUT = 1 + F R G
xVIP
(2)
Figure 39. Noise Sources in Typical Connection
(Noninverting gain, VIN = 0 V)
- RF VOUT = R G xVIN
(3)
(Inverting gain, VIP = 0 V)
Rev. B | Page 13 of 20
ADA4841-1/ADA4841-2
The output noise spectral density can be calculated by
vout _ en = R R 2 2 4 kTRf + 1 + F 4 kTRs + ien RS 2 + ven + F 4 kTRg + ien 2 R F 2 R R G G
2
[
]
2
(6) where: k is Boltzmann's Constant. T is the absolute temperature, degrees Kelvin. ien is the amplifier input current noise spectral density, pA/Hz. ven is the amplifier input voltage spectral density, nV/Hz. RS is the source resistance as shown in Figure 39. RF and RG are the feedback network resistances, as shown in Figure 39. Source resistance noise, amplifier voltage noise (ven), and the voltage noise from the amplifier current noise (ien x 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 and 30 k. Figure 40 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 and 1 k to keep the total noise low.
1000
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 41 and Figure 42 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 43, which avoids the output stage limitation.
300 260 220 180 140 100 60 20 -20 -60 -100 -140 -180 -260 -300 3.00 3.20 3.40 3.60 3.80 4.00 4.20 4.40 4.60
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COMMON-MODE ERROR (V)
+125C +25C -40C
-220
4.80 5.00
COMMON-MODE VOLTAGE (V)
Figure 41. +CMV vs. Common-Mode Error vs. VOS
0 -50 -100
COMMON-MODE ERROR (V)
-150 -200 -250 -300 -350 -400 -450 -500 -550 -600 -650
-40C +25C
100
NOISE (nV/ Hz)
AMPLIFIER + RESISTOR NOISE
+125C
10
TOTAL AMPLIFIER NOISE 1
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-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 COMMON-MODE VOLTAGE (V)
SOURCE RESISTANCE NOISE 0.1 10 100 1k SOURCE RESISTANCE () 10k
Figure 42. -CMV vs. Common-Mode Error vs. VOS
- VCM + + VOUT -
100k
Figure 40. 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. B | Page 14 of 20
Figure 43. Common-Range Subtractor
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05614-054
ADA4841-1/ADA4841-2
Figure 44 shows the amplifier frequency response as a G = -1 inverter with the input and output stage biased near the negative supply rail.
6 VS+ = 5V G = -1 VIN = 20mV p-p
60 G = +1 50
SERIES RESISTANCE ()
VS- = -150mV VS- = -100mV VS- = -200mV
40
3
VS- = -50mV 0
30
GAIN (dB)
20
-3
VS- = -20mV
10
-6
G = +5 0 10 100 1000
10000
-9
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CAPACITANCE LOAD (pF)
Figure 45. Series Resistance vs. Capacitance Load
-12 0.1
1
10 FREQUENCY (MHz)
100
INPUT PROTECTION
The ADA4841-1/ADA4841-2 are fully protected from ESD events, withstanding ESD events of 2.5 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 46.
VCC BIAS ESD VP ESD ESD VN ESD
Figure 44. Small Signal Frequency Response vs. Negative Supply Bias
The input voltage (VIN) and reference voltage (VIP) are both at 0 V, (see Figure 38). +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.
CAPACITANCE DRIVE
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. A small resistor in series with the amplifier output and the capacitive load mitigates the problem. Figure 45 plots the recommended series resistance vs. capacitance for gains of +1, +2, and +5.
VEE
05614-006
TO REST OF AMPLIFIER
Figure 46. 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. B | Page 15 of 20
05614-050
G = +2
ADA4841-1/ADA4841-2
POWER-DOWN OPERATION
Figure 47 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 A.
VCC IBIAS ESD POWER DOWN ESD TO AMPLIFIER BIAS
VEE
Figure 47. POWER DOWN Circuit
The POWER DOWN pin is protected with ESD clamps, as shown in Figure 47. 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.
05614-052
Rev. B | Page 16 of 20
ADA4841-1/ADA4841-2 APPLICATIONS
TYPICAL PERFORMANCE VALUES
To reduce design time and eliminate uncertainty Table 6 provides a convenient reference for typical gains, component values, and performance parameters.
RECONSTRUCTION FILTER
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 49 is a two-pole, 500 kHz Sallen-Key LPF with a fixed gain of G = +1.6.
C2 1320pF +5V 10F 0.1F R2 249 C1 1320pF
16-BIT ADC DRIVER
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 48 shows a typical 16-bit single-supply application. 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. 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 has no crossover region but has a wide linear input range from 100 mV below ground to 1 V below positive rail, solve this problem, as shown in Figure 48. 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 ADA48411/ADA4841-2 exhibits substantial nonlinearity, as any rail-torail 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.
+5.2V 100nF 10F
INPUT
R1 249
U1
0.1F 10F -5V
OUTPUT
R3 840
R4 499
Figure 49. 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 2R1C1
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
ADR364 100nF
Resistor values are kept low for minimal noise contribution, offset voltage, and optimal frequency response.
ADA4841 0V TO 4.096V
100nF 33 2.7nF REF IN+ VDD VIO SDI SCK SDO CNV
05614-060
-0.25V IN- GND
AD7685
Figure 48. ADC Driver Schematic
Rev. B | Page 17 of 20
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ADA4841-1/ADA4841-2
Table 6. Recommended Values and Typical Performance
Gain +1 +2 -1 +5 +10 +20 RF () 0 499 499 499 499 499 RG () N/A 499 499 124 54.9 26.1 -3 dB BW (MHz) 77 34 38 11 5 2.3 Slew Rate (V/s) 12.5 12.5 12.5 12 12 11.2 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
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 50 shows the filter response.
5 0 -5 -10
GAIN (dB)
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 49. 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. 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 F ceramic 0508 case be used. The 0508 case size offers low series inductance and excellent high frequency performance. A 10 F electrolytic capacitor should be placed in parallel with the 0.1 F 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.
-15 -20 -25 -30
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-35 -40 0.03
0.1
1 FREQUENCY (MHz)
10
Figure 50. 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.
Rev. B | Page 18 of 20
ADA4841-1/ADA4841-2 OUTLINE DIMENSIONS
5.00 (0.1968) 4.80 (0.1890)
8 5
4.00 (0.1574) 3.80 (0.1497) 1
6.20 (0.2440)
4 5.80 (0.2284)
1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0040)
1.75 (0.0688) 1.35 (0.0532)
0.50 (0.0196) x 45 0.25 (0.0099)
0.51 (0.0201) COPLANARITY SEATING 0.31 (0.0122) 0.10 PLANE
8 0.25 (0.0098) 0 1.27 (0.0500) 0.40 (0.0157) 0.17 (0.0067)
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.
Figure 51. 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 PIN 1
8
5
1
5.15 4.90 4.65
4
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 52. 8-Lead Mini Small Outline Package [MSOP] (RM-8) Dimensions shown in millimeters
Rev. B | Page 19 of 20
ADA4841-1/ADA4841-2
ORDERING GUIDE
Model ADA4841-1YRZ 1 ADA4841-1YRZ-R71 ADA4841-1YRZ-RL1 ADA4841-2YRMZ1 ADA4841-2YRMZ-R71 ADA4841-2YRMZ-RL1
1
Temperature Range -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C -40C to +125C
Package Description 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead SOIC_N 8-Lead MSOP 8-Lead MSOP 8-Lead MSOP
Package Option R-8 R-8 R-8 RM-8 RM-8 RM-8
Ordering Quantity 1 1,000 2,500 1 1,000 3,000
Z = Pb-free part.
(c) 2005 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D05614-0-10/05(B)
Rev. B | Page 20 of 20

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