LME49871 High Performance, High Fidelity Current Feedback Audio Operational Amplifier
April 28, 2008
LME49871 High Performance, High Fidelity Current Feedback Audio Operational Amplifier
General Description
The LME49871 is an ultra-low distortion, low noise, ultra high slew rate current feedback operational amplifier optimized and fully specified for high performance, high fidelity applications. Combining advanced leading-edge process technology with state-of-the-art circuit design, the LME49871 current feedback operational amplifier delivers superior signal amplification for outstanding performance. Operating on a wide supply range of ±5V to ±22V, the LME49871 combines extremely low voltage noise density (1.9nV/√Hz) with very low THD+N (0.00012%) to easily satisfy the most demanding applications. To ensure that the most challenging loads are driven without compromise, the LME49871 has a high slew rate of ±1900V/μs and an output current capability of ±100mA. Further, dynamic range is maximized by an output stage that drives 150Ω loads to within 2.9V of either power supply voltage. The LME49871 's outstanding CMRR (88dB), PSRR (102dB), and VOS (0.05mV) give the amplifier excellent operational amplifier DC performance. The LME49871 is available in an 8–lead narrow body SOIC. Demonstration boards are available.
Key Specifications
■ Power Supply Voltage Range ■ THD+N (AV = 1, RL = 100Ω, VOUT = 2VP-P, f = 1kHz) ■ THD+N (AV = 1, RL = 600Ω, VOUT = 1.4VRMS, f = 1kHz) ■ Input Noise Density ■ Slew Rate ■ Bandwidth
(AV = 1, RL= 2kΩ, RF = 800Ω) ±5V to ±22V
0.00021% (typ)
0.00012% (typ) 1.9nV/√Hz (typ) ±1900V/μs (typ) 213MHz (typ) 1.8μA (typ) 0.05mV (typ) 102dB (typ) 90dB (typ)
■ Input Bias Current ■ Input Offset Voltage ■ PSRR ■ CMRR
Features
■ ■ ■ ■
Easily drives 150Ω loads Optimized for superior audio signal fidelity Output short circuit protection SOIC package
Applications
■ ■ ■ ■ ■ ■ ■ ■ ■
Ultra high quality audio amplification High fidelity preamplifiers High fidelity multimedia State of the art phono pre amps High performance professional audio High fidelity equalization and crossover networks High performance line drivers High performance line receivers High fidelity active filters
© 2008 National Semiconductor Corporation
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LME49871
Connection Diagrams
SOIC Package
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Order Number LME49871MA See NS Package Number M08A LME49871MA Top Mark
30042602
N = National Logo Z = Assembly plant code X = 1 Digit date code TT = Die traceability L49871 = LME49871 MA = Package code
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LME49871
Absolute Maximum Ratings (Notes 1, 2)
If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Power Supply Voltage (VS = V+ - V-) Storage Temperature Input Voltage Output Short Circuit (Note 3) Power Dissipation 46V −65°C to 150°C (V-) - 0.7V to (V+) + 0.7V Continuous Internally Limited
ESD Rating (Note 4) ESD Rating (Note 5) Pins 1, 4, 7 and 8 Pins 2, 3, 5 and 6 Junction Temperature Thermal Resistance θJA (MA) Temperature Range TMIN ≤ TA ≤ TMAX Supply Voltage Range
2000V 200V 100V 150°C 145°C/W –40°C ≤ TA ≤ 85°C
±5.0V ≤ VS ≤ ±22V
Electrical Characteristics
Symbol Parameter
(Notes 1, 2) The following specifications apply for ±22V, RL = 2kΩ, RSOURCE = 10Ω, fIN = 1kHz, and TA = 25°C, unless otherwise specified. LME49871 Conditions AV = 1, f = 1kHz, RF = 1.2kΩ THD+N Total Harmonic Distortion + Noise RL = 100Ω, VOUT = 3VRMS RL = 600Ω, VOUT = 1.4VRMS IMD BW SR FPBW Intermodulation Distortion Bandwidth Slew Rate Full Power Bandwidth AV = 1, VIN = 3VRMS Two-tone, 60Hz & 7kHz 4:1 AV = –1, RF = 800Ω VOUT = 20VP-P, AV = –5 VOUT = 20VP-P, –3dB referenced to output magnitude at f = 1kHz, AV = 1 AV = –1, 10V step, 0.1% error range fBW = 20Hz to 20kHz f = 1kHz f = 10Hz f = 1kHz f = 10Hz 0.00021 0.00012 0.00009 213 ±1900 30 % % % MHz V/μs MHz Typical (Note 6) Limit (Note 7) Units (Limits)
ts
Settling Time Equivalent Input Noise Voltage
50 0.26 1.9 11.5 16 160 ±0.05 0.29 102 1.8 4.5 4.7 1.3 ±20.5 90 1.2 58 5 (V+) – 1.0 (V-) + 1.0 86 100 6 ±1.0 0.6 4.0
ns μVRMS (max)
en Equivalent Input Noise Density in VOS Current Noise Density Input Offset Voltage
nV/√Hz
(max)
pA/√Hz pA/√Hz
mV (max) μV/°C dB (min) μA (max) nA/°C nA/°C μA (max) V (min) V (min) dB (min) MΩ Ω MΩ (min) MΩ (min)
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Average Input Offset Voltage Drift vs ΔVOS/ΔTemp –40°C ≤ TA ≤ 85°C Temperature PSRR IB ΔIOS/ΔTemp IOS VIN-CM CMRR ZIN Average Input Offset Voltage Shift vs VS = ±22V, ΔVS = 30V (Note 8) Power Supply Voltage Input Bias Current Input Bias Current Drift vs Temperature Input Offset Current VCM = 0V –40°C ≤ TA ≤ 85°C Inverting input Non-inverting input VCM = 0V
Common-Mode Input Voltage Range VS = ±22V Common-Mode Rejection –10V ≤ VCM ≤ 10V –10V ≤ VCM ≤ 10V VOUT = ±10V RL = 200Ω RL = ∞
Non-inverting-input Input Impedance –10V ≤ VCM ≤ 10V Inverting-input Input Impedance Transimpedance
ZT
4.2 4.7
3
2.0 2.65
LME49871
LME49871 Symbol Parameter RL = 150Ω RL = 600Ω RL = 150Ω, VS = ±22V fIN = 5MHz Open-Loop IOUT = 0mA Conditions Typical (Note 6) VOUTMAX IOUT IOUT-CC ROUT IS ±18.6 ±19.4 ±100 ±140 10 8.3 9.5 Maximum Output Voltage Swing Output Current Instantaneous Short Circuit Current Output Resistance Total Quiescent Current Limit (Note 7) ±17.6 ±18.4 ±93
Units (Limits) V (min) V (min) mA (min) mA Ω mA (max)
Note 1: “Absolute Maximum Ratings” indicate limits beyond which damage to the device may occur, including inoperability and degradation of device reliability and/or performance. Functional operation of the device and/or non-degradation at the Absolute Maximum Ratings or other conditions beyond those indicated in the Recommended Operating Conditions is not implied. TheRecommended Operating Conditions indicate conditions at which the device is functional and the device should not be operated beyond such conditions. All voltages are measured with respect to the ground pin, unless otherwise specified. Note 2: The Electrical Characteristics tables list guaranteed specifications under the listed Recommended Operating Conditions except as otherwise modified or specified by the Electrical Characteristics Conditions and/or Notes. Typical specifications are estimations only and are not guaranteed. Note 3: Amplifier output connected to GND, any number of amplifiers within a package. Note 4: Human body model, applicable std. JESD22-A114C. Note 5: Machine model, applicable std. JESD22-A115-A. Note 6: Typical values represent most likely parametric norms at TA = +25ºC, and at the Recommended Operation Conditions at the time of product characterization and are not guaranteed. Note 7: Datasheet min/max specification limits are guaranteed by test or statistical analysis. Note 8: PSRR is measured as follows: VOS is measured at two supply voltages, ±7V and ±22V. PSRR = | 20log(ΔVOS/ΔVS) |.
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LME49871
Typical Performance Characteristics
FFT of 1kHz Sinewave, 0dBr Input Magnitude VOUT = 3VRMS, RL = 1kΩ, VS = ±15V, AV = 1 FFT of 1kHz Sinewave, 0dBr Input Magnitude VOUT = 3VRMS, RL = 100Ω, VS = ±15V, AV = 1
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FFT of 1kHz Sinewave, 0dBr Input Magnitude VOUT = 3VRMS, RL = 600Ω, VS = ±15V, AV = 1
FFT of 1kHz Sinewave, 0dBr Input Magnitude VOUT = 1.4VRMS, RL = 1kΩ, VS = ±15V, AV = 1
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FFT of 1kHz Sinewave, 0dBr Input Magnitude VOUT = 1.4VRMS, RL = 100Ω, VS = ±15V, AV = 1
FFT of 1kHz Sinewave, 0dBr Input Magnitude VOUT = 1.4VRMS, RL = 600Ω, VS = ±15V, AV = 1
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LME49871
FFT of 1kHz Sinewave, 0dBr Input Magnitude VOUT = 3VRMS, RL = 1kΩ, VS = ±22V, AV = 1
FFT of 1kHz Sinewave, 0dBr Input Magnitude VOUT = 3VRMS, RL = 100Ω, VS = ±22V, AV = 1
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FFT of 1kHz Sinewave, 0dBr Input Magnitude VOUT = 3VRMS, RL = 600Ω, VS = ±22V, AV = 1
FFT of 1kHz Sinewave, 0dBr Input Magnitude VOUT = 1.4VRMS, RL = 1kΩ, VS = ±22V, AV = 1
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FFT of 1kHz Sinewave, 0dBr Input Magnitude VOUT = 1.4VRMS, RL = 100Ω, VS = ±22V, AV = 1
FFT of 1kHz Sinewave, 0dBr Input Magnitude VOUT = 1.4VRMS, RL = 600Ω, VS = ±22V, AV = 1
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Output Voltage vs Supply Voltage AV = 1, RL = 600Ω, 1% THD+N
Output Voltage vs Supply Voltage AV = 1, RL = open, 1% THD+N
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Supply Current (ICC) vs Power Supply RL = open
Gain vs Frequency VS = ±15V, G = –1
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Gain vs Frequency VS = ±15V, G = –2
Gain vs Frequency VS = ±15V, G = –5
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LME49871
Gain vs Frequency VS = ±15V, G = –10
Gain vs Frequency VS = ±15V, RF = 800Ω
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Gain vs Frequency VS = ±15V, RF = 1.2kΩ
Gain vs Frequency VS = ±15V, RF = 2kΩ
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Gain vs Frequency VS = ±15V, RF = 3kΩ
Gain vs Frequency VS = ±22V, RF = 1.2kΩ
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LME49871
Gain vs Frequency VS = ±22V, RF = 2kΩ
Gain vs Frequency VS = ±22V, RF = 3kΩ
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Gain vs Frequency VS = ±22V, RF = 800Ω
Gain vs Frequency VS = ±22V, AV = –1
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Gain vs Frequency VS = ±22V, AV = –2
Gain vs Frequency VS = ±22V, AV = –5
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LME49871
Gain vs Frequency VS = ±22V, AV = –10
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LME49871
Application Information
GENERAL AMPLIFIER FUNCTION oltage feedback amplifiers have a small-signal bandwidth that is a function of the closed-loop gain. Conversely, the LME49871 current feedback amplifier features a small-signal bandwidth that is relatively independent of the closed-loop gain. This is shown in Figure 1 where the LME49871’s gain is –1,–2, –5 and –10. Like all current feedback amplifiers, the LME49871’s closed-loop bandwidth is a function of the feedback resistance value. Therefore, Rs must be varied to select the desired closed-loop gain. POWER SUPPLY BYPASSING AND LAYOUT CONSIDERATIONS Properly placed and correctly valued supply bypassing is essential for optimized high-speed amplifier operation. The supply bypassing must maintain a wideband, low-impedance capacitive connection between the amplifier’s supply pin and ground. This helps preserve high speed signal and fast transient fidelity. The bypassing is easily accomplished using a parallel combination of a 10μF tantalum and a 0.1μF ceramic capacitors for each power supply pin. The bypass capacitors should be placed as close to the amplifier power supply pins as possible. FEEDBACK RESISTOR SELECTION (Rf) The value of the Rf, is also a dominant factor in compensating the LME49871. For general applications, the LME49871 will maintain specified performance with an 1.2kΩ feedback resistor. Although this value will provide good results for most applications, it may be advantageous to adjust this value slightly for best pulse response optimized for the desired bandwidth. In addition to reducing bandwidth, increasing the feedback resistor value also reduces overshoot in the time domain response.
SLEW RATE CONSIDERATIONS A current feedback amplifier’s slew rate characteristics are different than that of voltage feedback amplifiers. A voltage feedback amplifier’s slew rate limiting or non-linear amplifier behavior is dominated by the finite availability of the first stage tail current charging the second stage voltage amplifier’s compensation capacitor. Conversely, a current feedback amplifier’s slew rate is not constant. Transient current at the inverting input determines slew rate for both inverting and non-inverting gains. The non-inverting configuration slew rate is also determined by input stage limitations. Accordingly, variations of slew rates occur for different circuit topologies. DRIVING CAPACITIVE LOADS The LME49871 can drive significantly higher capacitive loads than many current feedback amplifiers. Although the LME49871 can directly drive as much as 100pF without oscillating, the resulting response will be a function of the feedback resistor value. CAPACITIVE FEEDBACK It is quite common to place a small lead-compensation capacitor in parallel with a voltage feedback amplifier’s feedback resistance, Rf. This compensation reduces the amplifier’s peaking in the frequency domain and damps the transient response. Whereas this yields the expected results when used with voltage feedback amplifiers, this technique must not be used with current feedback amplifiers. The dynamic impedance of capacitors in the feedback loop reduces the amplifier’s stability. Instead, reduced peaking in the frequency response and bandwidth limiting can be accomplished by adding an RC circuit to the amplifier’s input.
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FIGURE 1. Bandwidth as a function of gain
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LME49871
Revision History
Rev 1.0 1.01 Date 04/24/08 04/28/08 Description Initial release. Changed the Limit values on VIN-CM from –2.0 and +2.0 to –1.0 and +1.0.
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LME49871
Physical Dimensions inches (millimeters) unless otherwise noted
SOIC Package Order Number LME49871MA NS Package Number M08A
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LME49871 High Performance, High Fidelity Current Feedback Audio Operational Amplifier
Notes
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