很完整的AD637资料

High Precision, Wideband RMS-to-DC Converter AD637 Rev. K 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 ©2011 Analog Devices, Inc. All rights reserved. FEATURES High accuracy 0.02% maximum nonlinearity, 0 V to 2 V rms input 0.10% additional error to crest factor of 3 Wide bandwidth 8 MHz at 2 V rms input 600 kHz at 100 mV rms Computes True rms Square Mean square Absolute value dB output (60 dB range) Chip select/power-down feature allows Analog three-state operation Quiescent current reduction from 2.2 mA to 350 μA 14-lead SBDIP, 14-lead low cost CERDIP, and 16-lead SOIC_W FUNCTIONAL BLOCK DIAGRAM ABSOLUTE VALUE DEN INPUT RMS OUT dB OUTPUT BUFF IN BUFF OUT 25kΩ 25kΩ COMMON CS OUTPUT OFFSET 00 78 8- 00 1 SQUARER/ DIVIDER BIAS VIN CAV AD637 Figure 1. GENERAL DESCRIPTION The AD637 is a complete, high accuracy, monolithic rms-to-dc converter that computes the true rms value of any complex waveform. It offers performance that is unprecedented in integrated circuit rms-to-dc converters and comparable to discrete and modular techniques in accuracy, bandwidth, and dynamic range. A crest factor compensation scheme in the AD637 permits measurements of signals with crest factors of up to 10 with less than 1% additional error. The wide band- width of the AD637 permits the measurement of signals up to 600 kHz with inputs of 200 mV rms and up to 8 MHz when the input levels are above 1 V rms. As with previous monolithic rms converters from Analog Devices, Inc., the AD637 has an auxiliary dB output available to users. The logarithm of the rms output signal is brought out to a separate pin, allowing direct dB measurement with a useful range of 60 dB. An externally programmed reference current allows the user to select the 0 dB reference voltage to correspond to any level between 0.1 V and 2.0 V rms. A chip select connection on the AD637 permits the user to decrease the supply current from 2.2 mA to 350 μA during periods when the rms function is not in use. This feature facilitates the addition of precision rms measurement to remote or handheld applications where minimum power consumption is critical. In addition, when the AD637 is powered down, the output goes to a high impedance state. This allows several AD637s to be tied together to form a wideband true rms multiplexer. The input circuitry of the AD637 is protected from overload voltages in excess of the supply levels. The inputs are not damaged by input signals if the supply voltages are lost. The AD637 is available in accuracy Grade J and Grade K for commercial temperature range (0°C to 70°C) applications, accuracy Grade A and Grade B for industrial range (−40°C to +85°C) appli- cations, and accuracy Grade S rated over the −55°C to +125°C temperature range. All versions are available in hermetically sealed, 14-lead SBDIP, 14-lead CERDIP, and 16-lead SOIC_W packages. The AD637 computes the true root mean square, mean square, or absolute value of any complex ac (or ac plus dc) input waveform and gives an equivalent dc output voltage. The true rms value of a waveform is more useful than an average rectified signal because it relates directly to the power of the signal. The rms value of a statistical signal is also related to the standard deviation of the signal. The AD637 is laser wafer trimmed to achieve rated performance without external trimming. The only external component required is a capacitor that sets the averaging time period. The value of this capacitor also determines low frequency accuracy, ripple level, and settling time. The on-chip buffer amplifier can be used either as an input buffer or in an active filter configuration. The filter can be used to reduce the amount of ac ripple, thereby increasing accuracy. AD637 Rev. K | Page 2 of 20 TABLE OF CONTENTS Features .............................................................................................. 1  Functional Block Diagram .............................................................. 1  General Description ......................................................................... 1  Revision History ............................................................................... 2  Specifications..................................................................................... 3  Absolute Maximum Ratings............................................................ 5  ESD Caution.................................................................................. 5  Pin Configurations and Function Descriptions ........................... 6  Functional Description .................................................................... 7  Standard Connection ................................................................... 8  Chip Select..................................................................................... 8  Optional Trims for High Accuracy ............................................ 8  Choosing the Averaging Time Constant....................................9  Frequency Response .................................................................. 11  AC Measurement Accuracy and Crest Factor ........................ 12  Connection for dB Output........................................................ 12  dB Calibration............................................................................. 13  Low Frequency Measurements................................................. 14  Vector Summation ..................................................................... 14  Evaluation Board ............................................................................ 16  Outline Dimensions ....................................................................... 19  Ordering Guide .......................................................................... 20  REVISION HISTORY 2/11—Rev. J to Rev. K Changes to Figure 15...................................................................... 11 Changes to Figure 16...................................................................... 12 Changes to Evaluation Board Section and Figure 23................. 16 Added Figure 24; Renumbered Sequentially .............................. 17 Changes to Figure 25 Through Figure 29.................................... 17 Changes to Figure 30...................................................................... 18 Added Figure 31.............................................................................. 18 Deleted Table 6; Renumbered Sequentially ................................ 18 Changes to Ordering Guide .......................................................... 20 4/07—Rev. I to Rev. J Added Evaluation Board Section ................................................. 16 Updated Outline Dimensions ....................................................... 20 10/06—Rev. H to Rev. I Changes to Table 1............................................................................ 3 Changes to Figure 4.......................................................................... 7 Changes to Figure 7.......................................................................... 9 Changes to Figure 16, Figure 18, and Figure 19 ......................... 12 Changes to Figure 20...................................................................... 13 12/05—Rev. G to Rev. H Updated Format..................................................................Universal Changes to Figure 1.......................................................................... 1 Changes to Figure 11...................................................................... 10 Updated Outline Dimensions ....................................................... 16 Changes to Ordering Guide .......................................................... 17 4/05—Rev. F to Rev. G Updated Format..................................................................Universal Changes to Figure 1...........................................................................1 Changes to General Description .....................................................1 Deleted Product Highlights .............................................................1 Moved Figure 4 to Page ....................................................................8 Changes to Figure 5...........................................................................9 Changes to Figure 8........................................................................ 10 Changes to Figure 11, Figure 12, Figure 13, and Figure 14....... 11 Changes to Figure 19...................................................................... 14 Changes to Figure 20...................................................................... 14 Changes to Figure 21...................................................................... 16 Updated Outline Dimensions....................................................... 17 Changes to Ordering Guide .......................................................... 18 3/02—Rev. E to Rev. F Edits to Ordering Guide ...................................................................3 AD637 Rev. K | Page 3 of 20 SPECIFICATIONS At 25°C and ±15 V dc, unless otherwise noted.1 Table 1. AD637J/AD637A AD637K/AD637B AD637S Parameter Min Typ Max Min Typ Max Min Typ Max Unit TRANSFER FUNCTION VOUT = 2IN )(V avg × VOUT = 2IN )(V avg × VOUT = 2IN )(V avg × CONVERSION ACCURACY Total Error, Internal Trim2 (Figure 5) ±1 ± 0.5 ±0.5 ± 0.2 ±1 ± 0.5 mV ±% of reading TMIN to TMAX ±3.0 ± 0.6 ±2.0 ± 0.3 ±6 ± 0.7 mV ± % of reading vs. Supply +VIN = 300 mV 30 150 30 150 30 150 μV/V vs. Supply −VIN = −300 mV 100 300 100 300 100 300 μV/V DC Reversal Error at 2 V 0.25 0.1 0.25 % of reading Nonlinearity 2 V Full Scale3 0.04 0.02 0.04 % of FSR Nonlinearity 7 V Full Scale 0.05 0.05 0.05 % of FSR Total Error, External Trim ±0.5 ± 0.1 ±0.25 ± 0.05 ±0.5 ± 0.1 mV ± % of reading ERROR VS. CREST FACTOR4 Crest Factor 1 to 2 Specified accuracy Specified accuracy Specified accuracy Crest Factor = 3 ±0.1 ±0.1 ±0.1 % of reading Crest Factor = 10 ±1.0 ±1.0 ±1.0 % of reading AVERAGING TIME CONSTANT 25 25 25 ms/μF CAV INPUT CHARACTERISTICS Signal Range, ±15 V Supply Continuous RMS Level 0 to 7 0 to 7 0 to 7 V rms Peak Transient Input ±15 ±15 ±15 V p-p Signal Range, ±5 V Supply Continuous RMS Level 0 to 4 0 to 4 0 to 4 V rms Peak Transient Input ±6 ±6 ±6 V p-p Maximum Continuous Nondestructive Input Level (All Supply Voltages) ±15 ±15 ±15 V p-p Input Resistance 6.4 8 9.6 6.4 8 9.6 6.4 8 9.6 kΩ Input Offset Voltage ±0.5 ±0.2 ±0.5 mV FREQUENCY RESPONSE5 Bandwidth for 1% Additional Error (0.09 dB) VIN = 20 mV 11 11 11 kHz VIN = 200 mV 66 66 66 kHz VIN = 2 V 200 200 200 kHz ±3 dB Bandwidth VIN = 20 mV 150 150 150 kHz VIN = 200 mV 1 1 1 MHz VIN = 2 V 8 8 8 MHz AD637 Rev. K | Page 4 of 20 AD637J/AD637A AD637K/AD637B AD637S Parameter Min Typ Max Min Typ Max Min Typ Max Unit OUTPUT CHARACTERISTICS Offset Voltage ±1 ±0.5 ±1 mV vs. Temperature ±0.05 ±0.089 ±0.04 ±0.056 ±0.04 ±0.07 mV/°C Voltage Swing, ±15 V Supply, 2 kΩ Load 0 to 12.0 13.5 0 to 12.0 13.5 0 to 12.0 13.5 V Voltage Swing, ±3 V Supply, 2 kΩ Load 0 to 2 2.2 0 to 2 2.2 0 to 2 2.2 V Output Current 6 6 6 mA Short-Circuit Current 20 20 20 mA Resistance Chip Select High 0.5 0.5 0.5 Ω Resistance Chip Select Low 100 100 100 kΩ dB OUTPUT Error, VIN 7 mV to 7 V rms, 0 dB = 1 V rms ±0.5 ±0.3 ±0.5 dB Scale Factor −3 −3 −3 mV/dB Scale Factor Temperature Coefficient +0.33 +0.33 +0.33 % of reading/°C −0.033 −0.033 −0.033 dB/°C IREF for 0 dB = 1 V rms 5 20 80 5 20 80 5 20 80 μA IREF Range 1 100 1 100 1 100 μA BUFFER AMPLIFIER Input Output Voltage Range −VS to (+VS − 2.5 V) −VS to (+VS − 2.5 V) −VS to (+VS − 2.5 V) V Input Offset Voltage ±0.8 ±2 ±0.5 ±1 ±0.8 ±2 mV Input Current ±2 ±10 ±2 ±5 ±2 ±10 nA Input Resistance 108 108 108 Ω Output Current −0.13 +5 −0.13 +5 −0.13 +5 mA Short-Circuit Current 20 20 20 mA Small Signal Bandwidth 1 1 1 MHz Slew Rate6 5 5 5 V/μs DENOMINATOR INPUT Input Range 0 to 10 0 to 10 0 to 10 V Input Resistance 20 25 30 20 25 30 20 25 30 kΩ Offset Voltage ±0.2 ±0.5 ±0.2 ±0.5 ±0.2 ±0.5 mV CHIP SELECT (CS) RMS On Level Open or 2.4 V < VC < +VS Open or 2.4 V < VC < +VS Open or 2.4 V < VC < +VS RMS Off Level VC < 0.2 V VC < 0.2 V VC < 0.2 V IOUT of Chip Select CS Low 10 10 10 μA CS High 0 0 0 μA On Time Constant 10 + ((25 kΩ) × CAV) 10 + ((25 kΩ) × CAV) 10 + ((25 kΩ) × CAV) μs Off Time Constant 10 + ((25 kΩ) × CAV) 10 + ((25 kΩ) × CAV) 10 + ((25 kΩ) × CAV) μs POWER SUPPLY Operating Voltage Range ±3.0 ±18 ±3.0 ±18 ±3.0 ±18 V Quiescent Current 2.2 3 2.2 3 2.2 3 mA Standby Current 350 450 350 450 350 450 μA 1 Specifications shown in bold are tested on all production units at final electrical test. Results from those tests are used to calculate outgoing quality levels. All minimum and maximum specifications are guaranteed, although only those shown in boldface are tested on all production units. 2 Accuracy specified 0 V rms to 7 V rms dc with AD637 connected, as shown in . Figure 5 3 Nonlinearity is defined as the maximum deviation from the straight line connecting the readings at 10 mV and 2 V. 4 Error vs. crest factor is specified as additional error for 1 V rms. 5 Input voltages are expressed in volts rms. Percent is in % of reading. 6 With external 2 kΩ pull-down resistor tied to −VS. AD637 Rev. K | Page 5 of 20 ABSOLUTE MAXIMUM RATINGS Table 2. Parameter Rating ESD Rating 500 V Supply Voltage ±18 V dc Internal Quiescent Power Dissipation 108 mW Output Short-Circuit Duration Indefinite Storage Temperature Range −65°C to +150°C Lead Temperature (Soldering 10 sec) 300°C Rated Operating Temperature Range AD637J, AD637K 0°C to 70°C AD637A, AD637B −40°C to +85°C AD637S, 5962-8963701CA −55°C to +125°C 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. ESD CAUTION AD637 Rev. K | Page 6 of 20 PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS BUFF IN 1 NC 2 COMMON 3 OUTPUT OFFSET 4 BUFF OUT14 VIN13 NC12 +VS11 CS 5 –VS10 DEN INPUT 6 RMS OUT9 dB OUTPUT 7 CAV8 NC = NO CONNECT AD637 TOP VIEW (Not to Scale) 00 78 8- 00 2 Figure 2. 14-Lead SBDIP/CERDIP Pin Configuration BUFF IN 1 NC 2 COMMON 3 OUTPUT OFFSET 4 BUFF OUT16 VIN15 NC14 +VS13 CS 5 –VS12 DEN INPUT 6 RMS OUT11 dB OUTPUT 7 CAV10 NC 8 NC9 NC = NO CONNECT AD637 TOP VIEW (Not to Scale) 00 78 8- 00 3 Figure 3. 16-Lead SOIC_W Pin Configuration Table 3. 14-Lead SBDIP/CERDIP Pin Function Descriptions Pin No. Mnemonic Description 1 BUFF IN Buffer Input 2, 12 NC No Connection 3 COMMON Analog Common 4 OUTPUT OFFSET Output Offset 5 CS Chip Select 6 DEN INPUT Denominator Input 7 dB OUTPUT dB Output 8 CAV Averaging Capacitor Connection 9 RMS OUT RMS Output 10 −VS Negative Supply Rail 11 +VS Positive Supply Rail 13 VIN Signal Input 14 BUFF OUT Buffer Output Table 4. 16-Lead SOIC_W Pin Function Descriptions Pin No. Mnemonic Description 1 BUFF IN Buffer Input 2, 8, 9, 14 NC No Connection 3 COMMON Analog Common 4 OUTPUT OFFSET Output Offset 5 CS Chip Select 6 DEN INPUT Denominator Input 7 dB OUTPUT dB Output 10 CAV Averaging Capacitor Connection 11 RMS OUT RMS Output 12 −VS Negative Supply Rail 13 +VS Positive Supply Rail 15 VIN Signal Input 16 BUFF OUT Buffer Output AD637 Rev. K | Page 7 of 20 FUNCTIONAL DESCRIPTION FILTER/AMPLIFIER 24kΩ 24kΩ ONE QUADRANT SQUARER/DIVIDER BUFFER AMPLIFIER Q1 Q2 Q3 Q4 125Ω 6kΩ6kΩ 12kΩ 24kΩ A5 A1 A2 ABSOLUTE VALUE VOLTAGE TO CURRENT CONVERTER I1 I3 I4 A4 A3 BIASQ5 CAV +VS RMS OUT COMMON CS DEN INPUT OUTPUT OFFSET dB OUTPUT AD637 BUFF OUT BUFF IN –VS 00 78 8- 00 4 14 1 13 10 4 6 5 3 7 9 11 8 VIN Figure 4. Simplified Schematic The AD637 embodies an implicit solution of the rms equation that overcomes the inherent limitations of straightforward rms computation. The actual computation performed by the AD637 follows the equation ⎥⎥⎦ ⎤ ⎢⎢⎣ ⎡= rmsV VAvgrmsV IN 2 Figure 4 is a simplified schematic of the AD637, subdivided into four major sections: absolute value circuit (active rectifier), squarer/divider, filter circuit, and buffer amplifier. The input voltage (VIN), which can be ac or dc, is converted to a unipolar current I1 by the active rectifiers A1 and A2. I1 drives one input of the squarer/divider, which has the transfer function 3 1 4 I II 2 = The output current of the squarer/divider I4 drives A4, forming a low-pass filter with the external averaging capacitor. If the RC time constant of the filter is much greater than the longest period of the input signal, then the A4 output is proportional to the average of I4. The output of this filter amplifier is used by A3 to provide the denominator current I3, which equals Avg I4 and is returned to the squarer/divider to complete the implicit rms computation rmsI I IAvgI 1 4 1 4 =⎥⎦ ⎤⎢⎣ ⎡= 2 and VOUT = VIN rms To compute the absolute value of the input signal, the averaging capacitor is omitted. However, a small capacitance value at the averaging capacitor pin is recommended to maintain stability; 5 pF is sufficient for this purpose. The circuit operates identically to that of the rms configuration, except that I3 is now equal to I4, giving 4 1 I I 2 4I = I4 = |I1| The denominator current can also be supplied externally by providing a reference voltage (VREF) to Pin 6. The circuit operates identically to the rms case, except that I3 is now proportional to VREF. Therefore, 3 1 I I Avg 2 4I = and DEN IN OUT V V V 2 = This is the mean square of the input signal. AD637 Rev. K | Page 8 of 20 STANDARD CONNECTION The AD637 is simple to connect for a majority of rms measurements. In the standard rms connection shown in Figure 5, only a single external capacitor is required to set the averaging time constant. In this configuration, the AD637 computes the true rms of any input signal. An averaging error, the magnitude of which is dependent on the value of the averaging capacitor, is present at low frequencies. For example, if the filter capacitor, CAV, is 4 μF, the error is 0.1% at 10 Hz and increases to 1% at 3 Hz. To measure ac signals, the AD637 can be ac-coupled by addin