Low Cost, Low Power, True RMS-to-DC Converter AD737 FUNCTIONAL BLOCK DIAGRAM Computes True rms value Average rectified value Absolute value Provides 200 mV full-scale input range (larger inputs with input attenuator) Direct interfacing with 31/2 digit CMOS ADCs High input impedance: 1012 Low input bias current: 25 pA maximum High accuracy: 0.2 mV 0.3% of reading RMS conversion with signal crest factors up to 5 Wide power supply range: 2.5 V to 16.5 V Low power: 160 A maximum supply current No external trims needed for specified accuracy A general-purpose, buffered voltage output version also available (AD736) AD737 8k CC 1 FULL-WAVE RECTIFIER VIN 2 8k INPUT AMPLIFIER POWER 3 DOWN 8 COM BIAS SECTION RMS CORE -VS 4 7 +VS 6 OUTPUT 5 CAV 00828-001 FEATURES Figure 1. GENERAL DESCRIPTION The AD7371 is a low power, precision, monolithic, true rms-to-dc converter. It is laser trimmed to provide a maximum error of 0.2 mV 0.3% of reading with sine wave inputs. Furthermore, it maintains high accuracy while measuring a wide range of input waveforms, including variable duty cycle pulses and triac (phase) controlled sine waves. The low cost and small physical size of this converter make it suitable for upgrading the performance of nonrms precision rectifiers in many applications. Compared to these circuits, the AD737 offers higher accuracy at equal or lower cost. Two signal input terminals are provided in the AD737. A high impedance (1012 ) FET input interfaces directly with high R input attenuators, and a low impedance (8 k) input accepts rms voltages to 0.9 V while operating from the minimum power supply voltage of 2.5 V. The two inputs can be used either single ended or differentially. The AD737 can compute the rms value of both ac and dc input voltages. It can also be operated ac-coupled by adding one external capacitor. In this mode, the AD737 can resolve input signal levels of 100 V rms or less, despite variations in temperature or supply voltage. High accuracy is also maintained for input waveforms with crest factors of 1 to 3. In addition, crest factors as high as 5 can be measured (while introducing only 2.5% additional error) at the 200 mV full-scale input level. The AD737 is available in four performance grades. The AD737J and AD737K grades are rated over the commercial temperature range of 0C to 70C. The AD737JR-5 is tested with supply voltages of 2.5 V dc. The AD737A and AD737B grades are rated over the industrial temperature range of -40C to +85C. The AD737 is available in three low cost, 8lead packages: PDIP, SOIC_N, and CERDIP. The AD737 has no output buffer amplifier, thereby significantly reducing dc offset errors occurring at the output, which makes the device highly compatible with high input impedance ADCs. Requiring only 160 A of power supply current, the AD737 is optimized for use in portable multimeters and other batterypowered applications. This converter also provides a power-down feature that reduces the power-supply standby current to less than 30 A. 1 The AD737 achieves 1% of reading error bandwidth, exceeding 10 kHz for input amplitudes from 20 mV rms to 200 mV rms, while consuming only 0.72 mW. PRODUCT HIGHLIGHTS 1. 2. 3. Capable of computing the average rectified value, absolute value, or true rms value of various input signals. Only one external component, an averaging capacitor, is required for the AD737 to perform true rms measurement. The low power consumption of 0.72 mW makes the AD737 suitable for battery-powered applications. Protected under U.S. Patent Number 5,495,245. Rev. H 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 (c)2008 Analog Devices, Inc. All rights reserved. AD737 TABLE OF CONTENTS Features .............................................................................................. 1 DC Error, Output Ripple, and Averaging Error ..................... 13 Functional Block Diagram .............................................................. 1 AC Measurement Accuracy and Crest Factor ........................ 13 General Description ......................................................................... 1 Calculating Settling Time.......................................................... 13 Product Highlights ........................................................................... 1 Applications Information .............................................................. 14 Revision History ............................................................................... 2 RMS Measurement--Choosing an Optimum Value for CAV ............................................................................... 14 Specifications..................................................................................... 3 Absolute Maximum Ratings............................................................ 6 Thermal Resistance ...................................................................... 6 ESD Caution .................................................................................. 6 Pin Configurations and Function Descriptions ........................... 7 Typical Performance Characteristics ............................................. 8 Theory of Operation ...................................................................... 12 Types of AC Measurement ........................................................ 12 Rapid Settling Times via the Average Responding Connection.................................................................................. 14 Selecting Practical Values for Capacitors ................................ 14 Scaling Input and Output Voltages .......................................... 14 AD737 Evaluation Board............................................................... 18 Outline Dimensions ....................................................................... 20 Ordering Guide .......................................................................... 22 REVISION HISTORY 10/08--Rev. G to Rev. H Added Selectable Average or RMS Conversion Section and Figure 27 .......................................................................................... 14 Updated Outline Dimensions ....................................................... 20 Changes to Ordering Guide .......................................................... 22 12/06--Rev. F to Rev. G Changes to Specifications ................................................................ 3 Reorganized Typical Performance Characteristics ...................... 8 Changes to Figure 21 ...................................................................... 11 Reorganized Theory of Operation Section ................................. 12 Reorganized Applications Section ................................................ 14 Added Scaling Input and Output Voltages Section.................... 14 Deleted Application Circuits Heading ......................................... 16 Changes to Figure 28 ...................................................................... 16 Added AD737 Evaluation Board Section .................................... 18 Updated Outline Dimensions ....................................................... 20 Changes to Ordering Guide .......................................................... 21 1/05--Rev. E to Rev. F Updated Format .................................................................. Universal Added Functional Block Diagram.................................................. 1 Changes to General Description Section ...................................... 1 Changes to Pin Configurations and Function Descriptions Section ........................................................................ 6 Changes to Typical Performance Characteristics Section ........... 7 Changes to Table 4 .......................................................................... 11 Change to Figure 24 ....................................................................... 12 Change to Figure 27 ....................................................................... 15 Changes to Ordering Guide .......................................................... 18 6/03--Rev. D to Rev. E Added AD737JR-5 .............................................................. Universal Changes to Features ..........................................................................1 Changes to General Description .....................................................1 Changes to Specifications .................................................................2 Changes to Absolute Maximum Ratings ........................................4 Changes to Ordering Guide .............................................................4 Added TPCs 16 through 19 .............................................................6 Changes to Figures 1 and 2 ..............................................................8 Changes to Figure 8 ........................................................................ 11 Updated Outline Dimensions ....................................................... 12 12/02--Rev. C to Rev. D Changes to Functional Block Diagram...........................................1 Changes to Pin Configuration .........................................................4 Figure 1 Replaced ..............................................................................8 Changes to Figure 2 ...........................................................................8 Figure 5 Replaced ........................................................................... 10 Changes to Application Circuits Figures 4, 6-8 ......................... 10 Outline Dimensions Updated ....................................................... 12 12/99--Rev. B to Rev. C Rev. H | Page 2 of 24 AD737 SPECIFICATIONS TA = 25C, VS = 5 V except as noted, CAV = 33 F, CC = 10 F, f = 1 kHz, sine wave input applied to Pin 2, unless otherwise specified. Specifications shown in boldface are tested on all production units at final electrical test. Results from these tests are used to calculate outgoing quality levels. Table 1. Parameter ACCURACY Total Error Conditions Min EIN = 0 to 200 mV rms VS = 2.5 V 0.2/0.3 VS = 2.5 V, input to Pin 1 EIN = 200 mV to 1 V rms Over Temperature AQ and BQ JN, JR, KN, KR AN and AR AD737A, AD737J Typ Max -1.2 EIN = 200 mV rms EIN = 200 mV rms, VS = 2.5 V EIN = 200 mV rms, VS = 2.5 V Min AD737B, AD737K Typ Max 0.2/0.2 0.4/0.5 -1.2 2.0 0.5/0.7 Min AD737J-5 Typ Max Unit 0.2/0.3 0.4/0.5 mV/POR1 mV/POR1 0.2/0.3 0.4/0.5 mV/POR1 0.2/0.3 POR 2.0 POR/C POR/C 0.3/0.5 0.007 0.007 0.014 0.014 0.02 POR/C Vs. Supply Voltage DC Reversal Error Nonlinearity2 Input to Pin 13 Total Error, External Trim ADDITIONAL CREST FACTOR ERROR4 For Crest Factors from 1 to 3 For Crest Factors from 3 to 5 INPUT CHARACTERISTICS High-Z Input (Pin 2) Signal Range Continuous RMS Level EIN = 200 mV rms, VS = 2.5 V to 5 V EIN = 200 mV rms, VS = 5 V to 16.5 V DC coupled, VIN = 600 mV dc VIN = 200 mV dc, VS = 2.5 V EIN = 0 mV to 200 mV rms, @ 100 mV rms AC coupled, EIN = 100 mV rms, after correction, VS = 2.5 V EIN = 0 mV to 200 mV rms CAV = CF = 100 F CAV = 22 F, CF = 100 F, VS = 2.5 V, input to Pin 1 CAV = CF = 100 F 0 -0.18 -0.3 0 -0.18 -0.3 0 -0.18 -0.3 %/V 0 0.06 0.1 0 0.06 0.1 0 0.06 0.1 %/V 1.3 2.5 1.3 2.5 1.7 0 0.25 0.35 0 0.25 0.1/0.2 0.7 0.7 0.1 0.1/0.2 % % 2.5 % 200 200 1 Rev. H | Page 3 of 24 POR mV/POR 1.7 2.5 POR POR 0.02 0.1/0.2 2.5 0.35 VS = +2.5 V VS = +2.8 V/-3.2 V VS = 5 V to 16.5 V POR 200 1 mV rms mV rms V rms AD737 Parameter Peak Transient Input Input Resistance Input Bias Current Low-Z Input (Pin 1) Signal Range Continuous RMS Level Peak Transient Input Conditions VS = +2.5 V input to Pin 1 VS = +2.8 V/-3.2 V VS = 5 V VS = 16.5 V Min OUTPUT CHARACTERISTICS Output Voltage Swing Output Resistance FREQUENCY RESPONSE High-Z Input (Pin 2) 1% Additional Error Min AD737B, AD737K Typ Max 0.9 AD737J-5 Typ Max 1012 1 4.0 1012 1 25 1012 1 25 VS = +2.5 V VS = +2.8 V/-3.2 V VS = 5 V to 16.5 V VS = +2.5 V 300 1 25 300 mV rms 300 1 mV rms V rms V 1.7 6.4 1.7 3.8 11 8 All supply voltages 9.6 12 AC coupled 3 VS = 2.5 V to 5 V VS = 5 V to 16.5 V No load 6.4 1.7 3.8 11 8 9.6 12 6.4 8 3 8 30 8 30 80 50 150 80 50 150 8 Unit V V V V pA 2.7 4.0 VS = 5 V Min 0.6 0.9 2.7 VS = +2.8 V/-3.2 V VS = 5 V VS = 16.5 V Input Resistance Maximum Continuous Nondestructive Input Input Offset Voltage5 Over the Rated Operating Temperature Range Vs. Supply AD737A, AD737J Typ Max 9.6 12 V V V k V p-p 3 mV 30 V/C 80 V/V V/V VS = +2.8 V/-3.2 V -1.6 -1.7 -1.6 -1.7 V VS = 5 V VS = 16.5 V VS = 2.5 V, input to Pin 1 DC -3.3 -4 -3.4 -5 -3.3 -4 -3.4 -5 V V V 6.4 8 9.6 6.4 8 9.6 -1.1 -0.9 6.4 8 9.6 k VIN = 1 mV rms 1 1 1 kHz VIN = 10 mV rms VIN = 100 mV rms VIN = 200 mV rms 6 37 33 6 37 33 6 37 33 kHz kHz kHz Rev. H | Page 4 of 24 AD737 Parameter 3 dB Bandwidth Low-Z Input (Pin 1) 1% Additional Error 3 dB Bandwidth POWER-DOWN MODE Disable Voltage Input Current, PD Enabled POWER SUPPLY Operating Voltage Range Current Conditions VIN = 1 mV rms VIN = 10 mV rms VIN = 100 mV rms VIN = 200 mV rms Min AD737A, AD737J Typ Max 5 55 170 190 Min AD737B, AD737K Typ Max 5 55 170 190 Min AD737J-5 Typ Max 5 55 170 190 Unit kHz kHz kHz kHz VIN = 1 mV rms 1 1 1 kHz VIN = 10 mV rms VIN = 40 mV rms VIN = 100 mV rms VIN = 200 mV rms VIN = 1 mV rms VIN = 10 mV rms VIN = 100 mV rms VIN = 200 mV rms 6 6 90 90 5 55 350 460 90 90 5 55 350 460 6 25 90 90 5 55 350 460 kHz kHz kHz kHz kHz kHz kHz kHz VPD = VS 0 11 0 11 +2.8/ -3.2 No input Rated input Powered down 5 16.5 120 170 25 160 210 40 +2.8/ -3.2 1 V A 5 16.5 120 170 25 160 210 40 2.5 5 16.5 V 120 170 25 160 210 40 A A A POR is % of reading. Nonlinearity is defined as the maximum deviation (in percent error) from a straight line connecting the readings at 0 V and at 200 mV rms. 3 After fourth-order error correction using the equation y = - 0.31009x4 - 0.21692x3 - 0.06939x2 + 0.99756x + 11.1 x 10-6 where y is the corrected result and x is the device output between 0.01 V and 0.3 V. 4 Crest factor error is specified as the additional error resulting from the specific crest factor, using a 200 mV rms signal as a reference. The crest factor is defined as VPEAK/V rms. 5 DC offset does not limit ac resolution. 2 Rev. H | Page 5 of 24 AD737 ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE Table 2. Parameter Supply Voltage Internal Power Dissipation Input Voltage Output Short-Circuit Duration Differential Input Voltage Storage Temperature Range CERDIP (Q-8) PDIP (N-8) and SOIC_N (R-8) Lead Temperature, Soldering (60 sec) ESD Rating JA is specified for the worst-case conditions, that is, a device soldered in a circuit board for surface-mount packages. Rating 16.5 V 200 mW VS Indefinite +VS and -VS Table 3. Thermal Resistance -65C to +150C -65C to +125C 300C 500 V Package Type 8-Lead CERDIP (Q-8) 8-Lead PDIP (N-8) 8-Lead SOIC_N (R-8) ESD CAUTION Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Rev. H | Page 6 of 24 JA 110 165 155 Unit C/W C/W C/W AD737 8 COM CC 1 7 +VS VIN 2 POWER DOWN 3 6 OUTPUT TOP VIEW -VS 4 (Not to Scale) 5 CAV Figure 2. SOIC_N Pin Configuration (R-8) 8 AD737 COM +VS TOP VIEW 6 OUTPUT POWER DOWN 3 (Not to Scale) 5 CAV -VS 4 CC 1 7 VIN 2 00828-003 AD737 00828-002 CC 1 VIN 2 Figure 3. CERDIP Pin Configuration (Q-8) Table 4. Pin Function Descriptions Pin No. 1 2 3 4 5 6 7 8 Mnemonic CC VIN POWER DOWN -VS CAV OUTPUT +VS COM Description Coupling Capacitor for Indirect DC Coupling. RMS Input. Disables the AD737. Low is enabled; high is powered down. Negative Power Supply. Averaging Capacitor. Output. Positive Power Supply. Common. Rev. H | Page 7 of 24 POWER DOWN 3 -VS 4 8 COM AD737 7 +VS TOP VIEW (Not to Scale) 6 OUTPUT 5 CAV Figure 4. PDIP Pin Configuration (N-8) 00828-004 PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS AD737 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25C, VS = 5 V (except AD737J-5, where VS = 2.5 V), CAV = 33 F, CC = 10 F, f = 1 kHz, sine wave input applied to Pin 2, unless otherwise specified. 10V VIN = 200mV rms CAV = 100F CF = 22F CAV = 22F, CF = 4.7F, CC = 22F 1V INPUT LEVEL (rms) 0.5 0.3 0.1 0 -0.1 100mV 1% ERROR 10mV -3dB 1mV -0.3 0 2 4 6 8 10 SUPPLY VOLTAGE (V) 12 14 100V 0.1 16 Figure 5. Additional Error vs. Supply Voltage 100 1000 10V DC COUPLED CAV = 22F, CF = 4.7F, CC = 22F 14 1V 12 INPUT LEVEL (rms) 10 PIN 1 8 PIN 2 6 100mV 1% ERROR 10mV 10% ERROR 4 1mV 0 2 4 6 8 10 SUPPLY VOLTAGE (V) 12 14 100V 0.1 16 Figure 6. Maximum Input Level vs. Supply Voltage 10 FREQUENCY (kHz) 100 1000 Figure 9. Frequency Response Driving Pin 2 6 ADDITIONAL ERROR (% of Reading) 25 20 15 00828-007 10 5 1 00828-009 0 -3dB 00828-006 2 0 2 4 6 8 10 12 14 DUAL SUPPLY VOLTAGE (V) 16 3ms BURST OF 1kHz = 3 CYCLES 200mV rms SIGNAL CC = 22F CF = 100F 5 CAV = 10F CAV = 33F 4 3 2 1 CAV = 100F 00828-010 PEAK INPUT BEFORE CLIPPING (V) 10 FREQUENCY (kHz) Figure 8. Frequency Response Driving Pin 1 16 SUPPLY CURRENT (A) 1 00828-008 -0.5 10% ERROR 00828-005 ADDITIONAL ERROR (% of Reading) 0.7 CAV = 250F 0 18 Figure 7. Supply Current (Power-Down Mode) vs. Supply Voltage (Dual) Rev. H | Page 8 of 24 1 2 3 4 CREST FACTOR (VPEAK /V rms) Figure 10. Additional Error vs. Crest Factor 5 AD737 1.0 VIN = 200mV rms CAV = 100F CF = 22F 0.5 0.4 0.2 0 -0.2 -0.4 -0.8 -60 -40 -20 0 20 40 60 80 TEMPERATURE (C) 100 120 -1.5 CAV = 22F, CC = 47F, CF = 4.7F 100mV INPUT LEVEL (rms) 1V 2V Figure 14. Error vs. RMS Input Level Using Circuit in Figure 30 100 500 VIN = 200mV rms CC = 47F CF = 47F AVERAGING CAPACITOR (F) 400 300 200 100 10 -0.5% 00828-012 -1% 0 0.2 0.4 0.6 RMS INPUT LEVEL (V) 0.8 1 10 1.0 Figure 12. DC Supply Current vs. RMS Input Level 00828-015 DC SUPPLY CURRENT (A) -1.0 -2.5 10mV 140 Figure 11. Additional Error vs. Temperature 0 -0.5 -2.0 00828-011 -0.6 0 00828-014 0.6 ERROR (% of Reading) ADDITIONAL ERROR (% of Reading) 0.8 100 FREQUENCY (Hz) 1k Figure 15. Value of Averaging Capacitor vs. Frequency for Specified Averaging Error 10mV 1V AC COUPLED -0.5% INPUT LEVEL (rms) 100V 10V 100 1k 10k -3dB FREQUENCY (Hz) Figure 13. RMS Input Level vs. -3 dB Frequency 100mV 10mV AC COUPLED CAV = 10F, CC = 47F, CF = 47F 1mV 100k 1 10 100 00828-016 1mV 00828-013 INPUT LEVEL (rms) -1% 1k FREQUENCY (Hz) Figure 16. RMS Input Level vs. Frequency for Specified Averaging Error Rev. H | Page 9 of 24 AD737 10nA 4.0 1nA INPUT BIAS CURRENT 3.0 2.5 2.0 10pA 1pA 00828-017 1.5 1.0 100pA 0 2 4 6 8 10 SUPPLY VOLTAGE (V) 12 14 100fA -55 16 Figure 17. Input Bias Current vs. Supply Voltage 00828-019 INPUT BIAS CURRENT (pA) 3.5 -35 -15 5 25 45 65 TEMPERATURE (C) 85 105 125 Figure 19. Input Bias Current vs. Temperature 1V 10V VS = 2.5V, CAV = 22F, CF = 4.7F, CC = 22F CC = 22F CF = 0F 1V CAV = 10F 10mV INPUT LEVEL (rms) INPUT LEVEL (rms) 100mV CAV = 100F CAV = 33F 100mV 10mV 1mV 10ms 100ms 1s SETTLING TIME 10s 100s Figure 18. RMS Input Level vs. Settling Time for Three Values of CAV 100V 0.1 00828-020 100V 1ms 00828-018 1mV 1 10 FREQUENCY (kHz) 100 Figure 20. Frequency Response Driving Pin 1 Rev. H | Page 10 of 24 1000 AD737 10V 1.0 VS = 2.5V, CAV = 22F, CF = 4.7F, CC = 22F 0.5 ERROR (% of Reading) INPUT LEVEL (rms) 1V 100mV 0.5% 10mV 0 -0.5 -1.0 -1.5 00828-021 -3dB 1% 100V 0.1 1 10 FREQUENCY (kHz) 100 1000 Figure 21. Error Contours Driving Pin 1 CAV = 10F CAV = 22F CAV = 33F 3 CAV = 100F 2 CAV = 220F 1 0 00828-022 ADDITIONAL ERROR (% of Reading) 4 1 2 3 CREST FACTOR 4 CAV = 22F, VS = 2.5V CC = 47F, CF = 4.7F -2.5 10mV 100mV INPUT LEVEL (rms) 1V Figure 23. Error vs. RMS Input Level Driving Pin 1 5 3 CYCLES OF 1kHz 200mV rms VS = 2.5V CC = 22F CF = 100F -2.0 00828-023 10% 1mV 5 Figure 22. Additional Error vs. Crest Factor for Various Values of CAV Rev. H | Page 11 of 24 2V AD737 THEORY OF OPERATION As shown in Figure 24, the AD737 has four functional subsections: an input amplifier, a full-wave rectifier, an rms core, and a bias section. The FET input amplifier allows a high impedance, buffered input at Pin 2 or a low impedance, wide dynamic range input at Pin 1. The high impedance input, with its low input bias current, is ideal for use with high impedance input attenuators. The input signal can be either dc-coupled or ac-coupled to the input amplifier. Unlike other rms converters, the AD737 permits both direct and indirect ac coupling of the inputs. AC coupling is provided by placing a series capacitor between the input signal and Pin 2 (or Pin 1) for direct coupling and between Pin 1 and ground (while driving Pin 2) for indirect coupling. AC CC = 10F + DC OPTIONAL RETURN PATH CURRENT MODE ABSOLUTE VALUE CC 8 1 8k COM VIN VIN + 2 8k 7 +VS CF 10F (OPTIONAL LPF) FET OP AMP 1B<10pA POWER DOWN 3 BIAS SECTION 6 OUTPUT 4 5 TYPES OF AC MEASUREMENT The AD737 is capable of measuring ac signals by operating as either an average responding converter or a true rms-to-dc converter. As its name implies, an average responding converter computes the average absolute value of an ac (or ac and dc) voltage or current by full-wave rectifying and low-pass filtering the input signal; this approximates the average. The resulting output, a dc average level, is then scaled by adding (or reducing) gain; this scale factor converts the dc average reading to an rms equivalent value for the waveform being measured. For example, the average absolute value of a sine wave voltage is 0.636 that of VPEAK; the corresponding rms value is 0.707 times VPEAK. Therefore, for sine wave voltages, the required scale factor is 1.11 (0.707 divided by 0.636). In contrast to measuring the average value, true rms measurement is a universal language among waveforms, allowing the magnitudes of all types of voltage (or current) waveforms to be compared to one another and to dc. RMS is a direct measure of the power or heating value of an ac voltage compared to that of a dc voltage; an ac signal of 1 V rms produces the same amount of heat in a resistor as a 1 V dc signal. CAV V rms = CA 33F + +VS POSITIVE SUPPLY 00828-024 0.1F COMMON 0.1F NEGATIVE SUPPLY Finally, the bias subsection permits a power-down function. This reduces the idle current of the AD737 from 160 A to 30 A. This feature is selected by connecting Pin 3 to Pin 7 (+VS). Mathematically, the rms value of a voltage is defined (using a simplified equation) as RMS TRANSLINEAR CORE -VS external averaging capacitor, CF. In the rms circuit, this additional filtering stage reduces any output ripple that was not removed by the averaging capacitor. -VS Figure 24. AD737 True RMS Circuit (Test Circuit) The output of the input amplifier drives a full-wave precision rectifier which, in turn, drives the rms core. It is the core that provides the essential rms operations of squaring, averaging, and square rooting, using an external averaging capacitor, CAV. Without CAV, the rectified input signal passes through the core unprocessed, as is done with the average responding connection (see Figure 26). In the average responding mode, averaging is carried out by an RC post filter consisting of an 8 k internal scale factor resistor connected between Pin 6 and Pin 8 and an Avg (V 2 ) This involves squaring the signal, taking the average, and then obtaining the square root. True rms converters are smart rectifiers; they provide an accurate rms reading regardless of the type of waveform being measured. However, average responding converters can exhibit very high errors when their input signals deviate from their precalibrated waveform; the magnitude of the error depends on the type of waveform being measured. As an example, if an average responding converter is calibrated to measure the rms value of sine wave voltages and then is used to measure either symmetrical square waves or dc voltages, the converter has a computational error 11% (of reading) higher than the true rms value (see Table 5). The transfer function for the AD737 is Rev. H | Page 12 of 24 V OUT = 2 Avg (V IN ) AD737 DC ERROR, OUTPUT RIPPLE, AND AVERAGING ERROR AC MEASUREMENT ACCURACY AND CREST FACTOR Figure 25 shows the typical output waveform of the AD737 with a sine wave input voltage applied. As with all real-world devices, the ideal output of VOUT = VIN is never exactly achieved; instead, the output contains both a dc and an ac error component. The crest factor of the input waveform is often overlooked when determining the accuracy of an ac measurement. Crest factor is defined as the ratio of the peak signal amplitude to the rms amplitude (crest factor = VPEAK/V rms). Many common waveforms, such as sine and triangle waves, have relatively low crest factors (2). Other waveforms, such as low duty cycle pulse trains and SCR waveforms, have high crest factors. These types of waveforms require a long averaging time constant to average out the long time periods between pulses. Figure 10 shows the additional error vs. the crest factor of the AD737 for various values of CAV. EO IDEAL EO DC ERROR = EO - EO (IDEAL) TIME 00828-026 AVERAGE EO = EO DOUBLE-FREQUENCY RIPPLE CALCULATING SETTLING TIME Figure 18 can be used to closely approximate the time required for the AD737 to settle when its input level is reduced in amplitude. The net time required for the rms converter to settle is the difference between two times extracted from the graph: the initial time minus the final settling time. As an example, consider the following conditions: a 33 F averaging capacitor, an initial rms input level of 100 mV, and a final (reduced) input level of 1 mV. From Figure 18, the initial settling time (where the 100 mV line intersects the 33 F line) is approximately 80 ms. The settling time corresponding to the new or final input level of 1 mV is approximately 8 seconds. Therefore, the net time for the circuit to settle to its new value is 8 seconds minus 80 ms, which is 7.92 seconds. Figure 25. Output Waveform for Sine Wave Input Voltage As shown, the dc error is the difference between the average of the output signal (when all the ripple in the output has been removed by external filtering) and the ideal dc output. The dc error component is, therefore, set solely by the value of the averaging capacitor used--no amount of post filtering (using a very large postfiltering capacitor, CF) allows the output voltage to equal its ideal value. The ac error component, an output ripple, can be easily removed using a large enough CF. In most cases, the combined magnitudes of the dc and ac error components must be considered when selecting appropriate values for CAV and CF capacitors. This combined error, representing the maximum uncertainty of the measurement, is termed the averaging error and is equal to the peak value of the output ripple plus the dc error. As the input frequency increases, both error components decrease rapidly. If the input frequency doubles, the dc error and ripple reduce to one-quarter and one-half of their original values, respectively, and rapidly become insignificant. Note that, because of the inherent smoothness of the decay characteristic of a capacitor/diode combination, this is the total settling time to the final value (not the settling time to 1%, 0.1%, and so on, of the final value). Also, this graph provides the worst-case settling time because the AD737 settles very quickly with increasing input levels. Table 5. Error Introduced by an Average Responding Circuit When Measuring Common Waveforms Type of Waveform 1 V Peak Amplitude Undistorted Sine Wave Symmetrical Square Wave Undistorted Triangle Wave Gaussian Noise (98% of Peaks <1 V) Rectangular Pulse Train SCR Waveforms 50% Duty Cycle 25% Duty Cycle Crest Factor (VPEAK/V rms) 1.414 1.00 1.73 True RMS Value (V) 0.707 1.00 0.577 Reading of an Average Responding Circuit Calibrated to an RMS Sine Wave Value (V) 0.707 1.11 0.555 Error (%) 0 11.0 -3.8 3 2 10 0.333 0.5 0.1 0.295 0.278 0.011 -11.4 -44 -89 2 4.7 0.495 0.212 0.354 0.150 -28 -30 Rev. H | Page 13 of 24 AD737 APPLICATIONS INFORMATION Because the external averaging capacitor, CAV, holds the rectified input signal during rms computation, its value directly affects the accuracy of the rms measurement, especially at low frequencies. Furthermore, because the averaging capacitor is connected across a diode in the rms core, the averaging time constant (AV) increases exponentially as the input signal decreases. It follows that decreasing the input signal decreases errors due to nonideal averaging but increases the settling time approaching the decreased rms-computed dc value. Thus, diminishing input values allow the circuit to perform better (due to increased averaging) while increasing the waiting time between measurements. A trade-off must be made between computational accuracy and settling time when selecting CAV. RAPID SETTLING TIMES VIA THE AVERAGE RESPONDING CONNECTION Because the average responding connection shown in Figure 26 does not use an averaging capacitor, its settling time does not vary with input signal level; it is determined solely by the RC time constant of CF and the internal 8 k output scaling resistor. CC AD737 8k 1 8 COM VIN FULL-WAVE RECTIFIER 2 8k INPUT AMPLIFIER POWER 3 DOWN BIAS SECTION + 6 VOUT +VS -VS 00828-025 0.1F NEGATIVE SUPPLY +VS 3 OUT 4 -V S CAV 7 +2.5V 6 VOUTDC 5 33F 33F NTR4501NT1 rms AVG ASSUMED TO BE A LOGIC SOURCE -2.5V Figure 27. CMOS Switch Is Used to Select RMS or Average Responding Modes SELECTING PRACTICAL VALUES FOR CAPACITORS Table 6 provides practical values of CAV and CF for several common applications. The input coupling capacitor, CC, in conjunction with the 8 k internal input scaling resistor, determines the -3 dB low frequency roll-off. This frequency, FL, is equal to FL = 1 2 x 8000 x C C ( in Farads ) (1) Note that, at FL, the amplitude error is approximately -30% (-3 dB) of reading. To reduce this error to 0.5% of reading, choose a value of CC that sets FL at one-tenth of the lowest frequency to be measured. The AD737 is an extremely flexible device. With minimal external circuitry, it can be powered with single- or dualpolarity power supplies, and input and output voltages are independently scalable to accommodate nonmatching I/O devices. This section describes a few such applications. 0.1F COMMON 1M 8 SCALING INPUT AND OUTPUT VOLTAGES 5 CAV POSITIVE SUPPLY 2 V IN VINRMS COM AD737 In addition, if the input voltage has more than 100 mV of dc offset, the ac coupling network at Pin 2 is required in addition to Capacitor CC. CF 33F OUTPUT RMS CORE -VS 4 7 +VS 1 CC 00828-039 RMS MEASUREMENT--CHOOSING AN OPTIMUM VALUE FOR CAV Figure 26. AD737 Average Responding Circuit Selectable Average or RMS Conversion For some applications, it is desirable to be able to select between rms-value-to-dc conversion and average-value-to-dc conversion. If CAV is disconnected from the root-mean core, the AD737 fullwave rectifier is a highly accurate absolute value circuit. A CMOS switch whose gate is controlled by a logic level selects between average and rms values. Extending or Scaling the Input Range For low supply voltage applications, the maximum peak voltage to the device is extended by simply applying the input voltage to Pin 1 across the internal 8 k input resistor. The AD737 input circuit functions quasi-differentially, with a high impedance FET input at Pin 2 (noninverting) and a low impedance input at Pin 1 (inverting, see Figure 26). The internal 8 k resistor behaves as a voltage-to-current converter connected to the summing node of a feedback loop around the input amplifier. Because the feedback loop acts to servo the summing node voltage to match the voltage at Pin 2, the maximum peak input voltage increases until the internal circuit runs out of headroom, approximately double for a symmetrical dual supply. Rev. H | Page 14 of 24 AD737 Battery Operation All the level-shifting for battery operation is provided by the 31/2 digit converter, shown in Figure 28. Alternatively, an external op amp adds flexibility by accommodating nonzero common-mode voltages and providing output scaling and offset to zero. When an external operational amplifier is used, the output polarity is positive going. Figure 29 shows an op amp used in a single-supply application. Note that the combined input resistor value (R1 + R2 + 8 k) matches that of the R5 feedback resistor. In this instance, the magnitudes of the output dc voltage and the rms of the ac input are equal. R3 and R4 provide current to offset the output to 0 V. Scaling the Output Voltage The output voltage can be scaled to the input rms voltage. For example, assume that the AD737 is retrofitted to an existing application using an averaging responding circuit (full-wave rectifier). The power supply is 12 V, the input voltage is 10 V ac, and the desired output is 6 V dc. For convenience, use the same combined input resistance as shown in Figure 29. Calculate the rms input current as I INMAG = 10 V = 125 A = I OUTMAG 69.8 k + 2.5 k + 8 k (2) Next, using the IOUTMAG value from Equation 2, calculate the feedback resistor required for 6 V output using R FB = 6V = 48.1 k 125 A (3) Select the closest-value standard 1% resistor, 47.5 k. Because the supply is 12 V, the common-mode voltage at the R7/R8 divider is 6 V, and the combined resistor value (R3 + R4) is equal to the feedback resistor, or 47.5 k. R2 is used to calibrate the transfer function (gain), and R4 sets the output voltage to zero with no input voltage. Perform calibration as follows: 1. 2. 3. With no ac input applied, adjust R4 for 0 V. Apply a known input to the input. Adjust the R2 trimmer until the input and output match. The op amp selected for any single-supply application must bea rail-to-rail type, for example an AD8541, as shown in Figure 29. For higher voltages, a higher voltage part, such as an OP196, can be used. When calibrating to 0 V, the specified voltage above ground for the operational amplifier must be taken into account. Adjust R4 slightly higher as appropriate. Table 6. AD737 Capacitor Selection Application General-Purpose RMS Computation RMS Input Level 0 V to 1 V 0 mV to 200 mV General-Purpose Average Responding 0 V to 1 V Audio Applications Speech Music 1 Maximum Crest Factor 5 200 Hz 20 Hz 200 Hz 20 Hz 5 5 5 CAV (F) 150 CF (F) 10 Settling Time 1 to 1% 360 ms 15 33 3.3 None 1 10 1 33 36 ms 360 ms 36 ms 1.2 sec 3.3 33 3.3 33 120 ms 1.2 sec 120 ms 1.2 sec 200 Hz 20 Hz 200 Hz 50 Hz 5 None None None 100 0 mV to 100 mV 60 Hz 50 Hz 60 Hz 5 5 5 82 50 47 27 33 27 1.0 sec 1.2 sec 1.0 sec 0 mV to 200 mV 0 mV to 100 mV 300 Hz 20 Hz 3 10 1.5 100 0.5 68 18 ms 2.4 sec 0 mV to 200 mV SCR Waveform Measurement Low Frequency Cutoff (-3 dB) 20 Hz 0 mV to 200 mV Settling time is specified over the stated rms input level with the input signal increasing from zero. Settling times are greater for decreasing amplitude input signals. Rev. H | Page 15 of 24 AD737 1F 20k +VS + AD589 1PRV 0.01F VIN + CC 10F CC 200mV 1 200k 1.23V COM AD737 8k TYPE CONVERTER 8 50k 1N4148 9M FULL-WAVE RECTIFIER VIN 2V 2 900k 20V 47k 1W POWER DOWN -VS 10k REF LOW +V 7 COMMON OUTPUT BIAS SECTION 3 200V REF HIGH +VS 8k INPUT AMPLIFIER 1N4148 90k 31/2 DIGIT ICL7136 1M 0.1F 1F 9V ANALOG CAV RMS CORE 4 + LOW 6 HIGH 5 + + -VS 33F 00828-027 SWITCH CLOSED ACTIVATES POWER-DOWN MODE. AD737 DRAWS JUST 40A IN THIS MODE Figure 28. 31/2 Digit DVM Circuit INPUT INPUT SCALE FACTOR ADJ R1 R2 C1 69.8k 5k 0.47F 1% 1 CF 0.47F COM 8 NC CC 5V 2 VIN +VS 7 C2 0.01F POWER DOWN R4 5k R5 80.6k 5V AD737 3 R3 78.7k OUTPUT ZERO ADJUST 0.01F 1 OUTPUT 6 2 7 AD8541AR 4 CAV 5 -VS 6 OUTPUT 5 3 4 C3 0.01F 5V + C4 2.2F CAV 33F R7 100k 2.5V C5 + 1F 00828-028 R8 100k NC = NO CONNECT Figure 29. Battery-Powered Operation for 200 mV Maximum RMS Full-Scale Input CC 10F + 100 SCALE FACTOR ADJUST CC COM AD737 8k 1 8 200 VIN FULL-WAVE RECTIFIER 2 8k INPUT AMPLIFIER 7 +VS CF 10F + OUTPUT BIAS SECTION 6 -VS 4 VOUT CAV RMS CORE 5 + CAV 33F Figure 30. External Scale Factor Trim Rev. H | Page 16 of 24 00828-029 POWER 3 DOWN AD737 13 CC 10F CC + 1 COM VIN FULL-WAVE RECTIFIER 2 8k INPUT AMPLIFIER 14 1k 3500PPM/C 12 * AD737 8k Q1 8 NC PRECISION RESISTOR CORP TYPE PT/ST 60.4 SCALE FACTOR TRIM 7 +VS 2k OUTPUT POWER 3 DOWN BIAS SECTION 31.6k 2 6 AD711 -VS CAV RMS CORE 4 3 * 10 Q2 11 + IREF R1** 9 00828-030 NC = NO CONNECT *Q1, Q2 PART OF RCA CA3046 OR SIMILAR NPN TRANSISTOR ARRAY. 4.3V **R1 + RCAL IN = 10,000 x 0dB INPUT LEVEL IN V Figure 31. dB Output Connection OFFSET ADJUST 500k +VS -VS 1M 1k COM 499 8k AD737 1 VIN 2 FULL-WAVE RECTIFIER INPUT AMPLIFIER POWER DOWN 3 8 7 +VS 6 1k SCALE FACTOR ADJUST VOUT Figure 32. DC-Coupled Offset Voltage and Scale Factor Trims Rev. H | Page 17 of 24 00828-031 CC dB OUTPUT 100mV/dB 5 CAV RCAL ** 6 AD737 AD737 EVALUATION BOARD 00828-033 An evaluation board, AD737-EVALZ, is available for experiments or for becoming familiar with rms-to-dc converters. Figure 33 is a photograph of the board; Figure 35 to Figure 38 show the signal and power plane copper patterns. The board is designed for multipurpose applications and can be used for the AD736 as well. Although not shipped with the board, an optional socket that accepts the 8lead surface mount package is available from Enplas Corp. 00828-038 Figure 35. AD737 Evaluation Board--Component-Side Copper 00828-032 00828-034 Figure 33. AD737 Evaluation Board Figure 36. AD737 Evaluation Board--Secondary-Side Copper Figure 37. AD737 Evaluation Board--Internal Power Plane 00828-036 As described in the Applications Information section, the AD737 can be connected in a variety of ways. As shipped, the board is configured for dual supplies with the high impedance input connected and the power-down feature disabled. Jumpers are provided for connecting the input to the low impedance input (Pin 1) and for dc connections to either input. The schematic with movable jumpers is shown in Figure 39. The jumper positions in black are default connections; the dotted-outline jumpers are optional connections. The board is tested prior to shipment and requires only a power supply connection and a precision meter to perform measurements. Table 7 provides a bill of materials for the AD737 evaluation board. 00828-035 Figure 34. AD737 Evaluation Board--Component-Side Silkscreen Figure 38. AD737 Evaluation Board--Internal Ground Plane Rev. H | Page 18 of 24 AD737 -VS GND1 GND2 GND3 GND4 +VS C1 + 10F 25V W1 DC COUP LO-Z W4 LO-Z IN + C2 10F 25V -VS +VS W3 AC COUP R3 0 + CC J1 CIN 0.1F DUT P2 HI-Z SEL HI-Z AD737 1 IN COM CC 8 2 V IN GND 7 +VS 3 POWER DOWN OUTPUT 6 W2 R1 1M +VS 4 -VS J3 PD FILT NORM -VS SEL PIN3 CAV R4 0 +VS C6 0.1F 5 CAV VOUT J2 CF1 CAV 33 F 16V + C4 0.1F CF2 00828-037 VIN Figure 39. AD737 Evaluation Board Schematic Table 7. AD737 Evaluation Board Bill of Materials Qty 1 1 2 3 1 5 1 4 2 1 1 1 2 4 Name Test loop Test loop Capacitor Capacitor Capacitor Test loop Integrated circuit Test loop Connector Header Header Resistor Resistor Header Description Red Green Tantalum 10 F, 25 V 0.1 F, 16 V, 0603, X7R Tantalum 33 F, 16V, 20%, 6032 Purple RMS-to-DC converter Black BNC, right angle 6 pins, 2 x 3 3 pins 1 M, 1/10 W, 1%, 0603 0 , 5%, 0603 2 Pins, 0.1" center Reference Designator +VS -VS C1, C2 C4, C6, CIN CAV CAV, HI-Z, LO-Z, VIN, VOUT DUT GND1, GND2, GND3, GND4 J1, J2 J3 P2 R1 R3, R4 W1, W2, W3, W4 Rev. H | Page 19 of 24 Manufacturer Components Corp. Components Corp. Nichicon KEMET Nichicon Components Corp. Analog Devices, Inc. Components Corp. AMP 3M Molex Panasonic Panasonic Molex Mfg. Part Number TP-104-01-02 TP-104-01-05 F931E106MCC C0603C104K4RACTU F931C336MCC TP-104-01-07 AD737JRZ TP-104-01-00 227161-1 929836-09-03 22-10-2031 ERJ3EKF1004V ERJ3GEY0R00V 22-10-2021 AD737 OUTLINE DIMENSIONS 5.00 (0.1968) 4.80 (0.1890) 5 1 6.20 (0.2441) 5.80 (0.2284) 4 1.27 (0.0500) BSC 0.25 (0.0098) 0.10 (0.0040) 0.51 (0.0201) 0.31 (0.0122) COPLANARITY 0.10 SEATING PLANE 0.50 (0.0196) 0.25 (0.0099) 1.75 (0.0688) 1.35 (0.0532) 45 8 0 0.25 (0.0098) 0.17 (0.0067) 1.27 (0.0500) 0.40 (0.0157) COMPLIANT TO JEDEC STANDARDS MS-012-A A CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN. Figure 40. 8-Lead Standard Small Outline Package [SOIC_N] Narrow Body (R-8) Dimensions shown in millimeters and (inches) 0.005 (0.13) MIN 8 0.055 (1.40) MAX 5 0.310 (7.87) 0.220 (5.59) 1 4 0.100 (2.54) BSC 0.320 (8.13) 0.290 (7.37) 0.405 (10.29) MAX 0.060 (1.52) 0.015 (0.38) 0.200 (5.08) MAX 0.150 (3.81) MIN 0.200 (5.08) 0.125 (3.18) 0.023 (0.58) 0.014 (0.36) 0.070 (1.78) 0.030 (0.76) SEATING PLANE 15 0 0.015 (0.38) 0.008 (0.20) CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN. Figure 41. 8-Lead Ceramic Dual In-Line Package [CERDIP] (Q-8) Dimensions shown in inches and (millimeters) Rev. H | Page 20 of 24 012407-A 8 4.00 (0.1574) 3.80 (0.1497) AD737 0.400 (10.16) 0.365 (9.27) 0.355 (9.02) 8 5 1 4 0.280 (7.11) 0.250 (6.35) 0.240 (6.10) 0.100 (2.54) BSC 0.060 (1.52) MAX 0.210 (5.33) MAX 0.015 (0.38) MIN 0.150 (3.81) 0.130 (3.30) 0.115 (2.92) SEATING PLANE 0.022 (0.56) 0.018 (0.46) 0.014 (0.36) 0.325 (8.26) 0.310 (7.87) 0.300 (7.62) 0.195 (4.95) 0.130 (3.30) 0.115 (2.92) 0.015 (0.38) GAUGE PLANE 0.005 (0.13) MIN 0.014 (0.36) 0.010 (0.25) 0.008 (0.20) 0.430 (10.92) MAX COMPLIANT TO JEDEC STANDARDS MS-001 CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN. CORNER LEADS MAY BE CONFIGURED AS WHOLE OR HALF LEADS. Figure 42. 8-Lead Plastic Dual-In-Line Package [PDIP] (N-8) Dimensions shown in inches and (millimeters) Rev. H | Page 21 of 24 070606-A 0.070 (1.78) 0.060 (1.52) 0.045 (1.14) AD737 ORDERING GUIDE Model AD737AN AD737ANZ1 AD737AQ AD737AR AD737ARZ1 AD737BQ AD737JN AD737JNZ 1 AD737JR AD737JR-REEL AD737JR-REEL7 AD737JR-5 AD737JR-5-REEL AD737JR-5-REEL7 AD737JRZ1 AD737JRZ-R71 AD737JRZ-RL1 AD737JRZ-51 AD737JRZ-5-R71 AD737JRZ-5-RL1 AD737KN AD737KNZ1 AD737KR AD737KR-REEL AD737KR-REEL7 AD737KRZ1 AD737KRZ-RL1 AD737KRZ-R71 AD737-EVALZ1 1 Temperature Range -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C 0C to 70C 0C to 70C 0C to 70C 0C to 70C 0C to 70C 0C to 70C 0C to 70C 0C to 70C 0C to 70C 0C to 70C 0C to 70C 0C to 70C 0C to 70C 0C to 70C 0C to 70C 0C to 70C 0C to 70C 0C to 70C 0C to 70C 0C to 70C 0C to 70C 0C to 70C Package Description 8-Lead Plastic Dual In-Line Package [PDIP] 8-Lead Plastic Dual In-Line Package [PDIP] 8-Lead Ceramic Dual In-Line Package [CERDIP] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Ceramic Dual In-Line Package [CERDIP] 8-Lead Plastic Dual In-Line Package [PDIP] 8-Lead Plastic Dual In-Line Package [PDIP] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Plastic Dual In-Line Package [PDIP] 8-Lead Plastic Dual In-Line Package [PDIP] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Standard Small Outline Package [SOIC_N] 8-Lead Standard Small Outline Package [SOIC_N] Evaluation Board Z = RoHS Compliant Part. Rev. H | Page 22 of 24 Package Option N-8 N-8 Q-8 R-8 R-8 Q-8 N-8 N-8 R-8 R-8 R-8 R-8 R-8 R-8 R-8 R-8 R-8 R-8 R-8 R-8 N-8 N-8 R-8 R-8 R-8 R-8 R-8 R-8 AD737 NOTES Rev. H | Page 23 of 24 AD737 NOTES (c)2008 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D00828-0-10/08(H) Rev. H | Page 24 of 24