AD736JRZ

Low Cost, Low Power, True RMS-to-DC Converter AD736 Data Sheet FEATURES GENERAL DESCRIPTION The AD736 is a low power, precision, monolithic true rms-todc converter. It is laser trimmed to provide a maximum error of ±0.3 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 size of this converter make it suitable for upgrading the performance of non-rms precision rectifiers in many applications. Compared to these circuits, the AD736 offers higher accuracy at an equal or lower cost. The AD736 can compute the rms value of both ac and dc input voltages. It can also be operated as an ac-coupled device by adding one external capacitor. In this mode, the AD736 can resolve input signal levels of 100 μV 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 (introducing only 2.5% additional error) at the 200 mV full-scale input level. The AD736 has its own output buffer amplifier, thereby providing a great deal of design flexibility. Requiring only 200 µA of power supply current, the AD736 is optimized for use in portable multimeters and other battery-powered applications. FUNCTIONAL BLOCK DIAGRAM CC 8kΩ +VS OUT VIN FULL WAVE RECTIFIER RMS CORE CF 8kΩ CF (OPT) CAV BIAS SECTION COM CAV –VS 00834-001 Converts an ac voltage waveform to a dc voltage and then converts to the true rms, average rectified, or absolute value 200 mV rms full-scale input range (larger inputs with input attenuator) High input impedance: 1012 Ω Low input bias current: 25 pA maximum High accuracy: ±0.3 mV ± 0.3% of reading RMS conversion with signal crest factors up to 5 Wide power supply range: +2.8 V, −3.2 V to ±16.5 V Low power: 200 µA maximum supply current Buffered voltage output No external trims needed for specified accuracy Related device: the AD737—features a power-down control with standby current of only 25 μA; the dc output voltage is negative and the output impedance is 8 kΩ Figure 1. The AD736 allows the choice of two signal input terminals: a high impedance FET input (1012 Ω) that directly interfaces with High-Z input attenuators and a low impedance input (8 kΩ) that allows the measurement of 300 mV input levels while operating from the minimum power supply voltage of +2.8 V, −3.2 V. The two inputs can be used either single ended or differentially. The AD736 has a 1% reading error bandwidth that exceeds 10 kHz for the input amplitudes from 20 mV rms to 200 mV rms while consuming only 1 mW. The AD736 is available in four performance grades. The AD736J and AD736K grades are rated over the 0°C to +70°C and −20°C to +85°C commercial temperature ranges. The AD736A and AD736B grades are rated over the −40°C to +85°C industrial temperature range. The AD736 is available in three low cost, 8-lead packages: PDIP, SOIC, and CERDIP. PRODUCT HIGHLIGHTS 1. The AD736 is capable of computing the average rectified value, absolute value, or true rms value of various input signals. 2. Only one external component, an averaging capacitor, is required for the AD736 to perform true rms measurement. 3. The low power consumption of 1 mW makes the AD736 suitable for many battery-powered applications. 4. A high input impedance of 1012 Ω eliminates the need for an external buffer when interfacing with input attenuators. 5. A low impedance input is available for those applications that require an input signal up to 300 mV rms operating from low power supply voltages. Rev. I 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 ©1988–2012 Analog Devices, Inc. All rights reserved. AD736 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 RMS Measurement—Choosing the Optimum Value for CAV .... 11 General Description ......................................................................... 1 Functional Block Diagram .............................................................. 1 Rapid Settling Times via the Average Responding Connection .................................................................................. 12 Product Highlights ........................................................................... 1 DC Error, Output Ripple, and Averaging Error ..................... 12 Revision History ............................................................................... 2 AC Measurement Accuracy and Crest Factor............................ 12 Specifications..................................................................................... 3 Applications..................................................................................... 13 Absolute Maximum Ratings ............................................................ 5 Connecting the Input................................................................. 13 Thermal Resistance ...................................................................... 5 Selecting Practical Values for Input Coupling (CC), Averaging (CAV), and Filtering (CF) Capacitors ...................... 14 ESD Caution .................................................................................. 5 Pin Configuration and Function Descriptions ............................. 6 Typical Performance Characteristics ............................................. 7 Theory of Operation ...................................................................... 10 Types of AC Measurement ........................................................ 10 Additional Application Concepts............................................. 15 Evaluation Board ............................................................................ 17 Outline Dimensions ....................................................................... 19 Ordering Guide .......................................................................... 20 Calculating Settling Time Using Figure 16 ............................. 11 REVISION HISTORY 12/12—Rev. H to Rev. I Changes to Features and Figure 1.................................................. 1 Change to Error vs. Crest Factor Parameter, Table 1 .................. 3 Changes to Operating Voltage Range Parameter, Table 1 .......... 4 Changes to Table 2 ........................................................................... 5 Added Table 3; Renumbered Sequentially ................................... 5 Changes to Figure 9 ......................................................................... 8 Changes to Figure 16 ....................................................................... 9 Changes to Figure 18 ..................................................................... 10 Added Additional Application Concepts Section and Changes to Figure 25 ..................................................................... 15 Changes to Figure 29 ..................................................................... 17 Deleted Table 6 ............................................................................... 17 Changes to Ordering Guide ......................................................... 20 2/07—Rev. G to Rev. H Updated Layout .......................................................................9 to 12 Added Applications Section ......................................................... 13 Inserted Figure 21 to Figure 24; Renumbered Sequentially..... 13 Deleted Figure 25 ........................................................................... 15 Added Evaluation Board Section................................................. 16 Inserted Figure 29 to Figure 34; Renumbered Sequentially..... 16 Inserted Figure 35; Renumbered Sequentially........................... 17 Added Table 6................................................................................. 17 2/06—Rev. F to Rev. G Updated Format ................................................................. Universal Changes to Features .........................................................................1 Added Table 3 ...................................................................................6 Changes to Figure 21 and Figure 22 ........................................... 14 Changes to Figure 23, Figure 24, and Figure 25 ........................ 15 Updated Outline Dimensions ...................................................... 16 Changes to Ordering Guide ......................................................... 17 5/04—Rev. E to Rev. F Changes to Specifications ................................................................2 Replaced Figure 18 ........................................................................ 10 Updated Outline Dimensions ...................................................... 16 Changes to Ordering Guide ......................................................... 16 4/03—Rev. D to Rev. E Changes to General Description .................................................1 Changes to Specifications .............................................................3 Changes to Absolute Maximum Ratings ....................................4 Changes to Ordering Guide .........................................................4 11/02—Rev. C to Rev. D Changes to Functional Block Diagram.......................................1 Changes to Pin Configuration .....................................................3 Figure 1 Replaced ..........................................................................6 Changes to Figure 2 .......................................................................6 Changes to Application Circuits Figures 4 to 8 .........................8 Outline Dimensions Updated ......................................................8 Rev. I | Page 2 of 20 Data Sheet AD736 SPECIFICATIONS At 25°C ± 5 V supplies, ac-coupled with 1 kHz sine wave input applied, unless otherwise noted. Specifications in bold are tested on all production units at final electrical test. Results from those tests are used to calculate outgoing quality levels. Table 1. Parameter TRANSFER FUNCTION CONVERSION ACCURACY Total Error, Internal Trim 1 All Grades TMIN to TMAX A and B Grades J and K Grades vs. Supply Voltage @ 200 mV rms Input DC Reversal Error, DC-Coupled Nonlinearity 2, 0 mV to 200 mV Total Error, External Trim ERROR VS. CREST FACTOR 3 Crest Factor = 1 to 3 Crest Factor = 3 to 5 INPUT CHARACTERISTICS High Impedance Input Signal Range (Pin 2) Continuous RMS Level Peak Transient Input Input Resistance Input Bias Current Low Impedance Input Signal Range (Pin 1) Continuous RMS Level Peak Transient Input Input Resistance Maximum Continuous Nondestructive Input Input Offset Voltage 4 J and K Grades A and B Grades vs. Temperature vs. Supply Conditions Min AD736J/AD736A AD736K/AD736B Typ Max Min Typ Max VOUT = √Avg (VIN2) 1 kHz sine wave Using CC 0 mV rms to 200 mV rms 200 mV to 1 V rms 0.3/0.3 −1.2 @ 200 mV rms @ 200 mV rms 0.7/0.7 0.007 VS = ±5 V to ±16.5 V VS = ±5 V to ±3 V @ 600 mV dc @ 100 mV rms 0 mV rms to 200 mV rms 0 0 0 CAV, CF = 100 µF CAV, CF = 100 µF VS = +2.8 V, −3.2 V VS = ±5 V to ±16.5 V VS = +2.8 V, −3.2 V VS = ±5 V VS = ±16.5 V +0.06 −0.18 1.3 0.25 0.1/0.5 0.2/0.2 −1.2 +0.1 −0.3 2.5 0.35 0 0 0 +0.06 −0.18 1.3 0.25 0.1/0.3 ±0.9 0.5/0.5 ±mV/±% of reading ±% of reading/°C +0.1 −0.3 2.5 0.35 %/V %/V % of reading % of reading ±mV/±% of reading % additional error % additional error 200 1 ±0.9 ±2.7 ±2.7 ±4.0 ±4.0 1012 1 1012 1 25 300 1 6.4 ±mV/±% of reading % of reading 0.7 2.5 200 1 VS = +2.8 V, –3.2 V VS = ±5 V to ±16.5 V VS = +2.8 V, −3.2 V VS = ±5 V VS = ±16.5 V 0.3/0.3 ±2.0 0.007 0.7 2.5 VS = ±3 V to ±16.5 V ±1.7 ±3.8 ±11 8 All supply voltages VS = ±5 V to ±16.5 V VS = ±5 V to ±3 V 0.5/0.5 ±2.0 8 50 80 Rev. I | Page 3 of 20 9.6 ±12 ±3 ±3 30 150 25 300 1 6.4 ±1.7 ±3.8 ±11 8 8 50 80 Unit 9.6 ±12 ±3 ±3 30 150 mV rms V rms V V V Ω pA mV rms V rms V V V kΩ V p-p mV mV µV/°C µV/V µV/V AD736 Parameter OUTPUT CHARACTERISTICS Output Offset Voltage J and K Grades A and B Grades vs. Temperature vs. Supply Output Voltage Swing 2 kΩ Load Data Sheet Conditions Quiescent Current 200 mV rms, No Load TEMPERATURE RANGE Operating, Rated Performance Commercial Industrial AD736J/AD736A Typ Max ±0.1 1 50 50 VS = ±5 V to ±16.5 V VS = ±5 V to ±3 V VS = +2.8 V, −3.2 V VS = ±5 V No Load Output Current Short-Circuit Current Output Resistance FREQUENCY RESPONSE High Impedance Input (Pin 2) for 1% Additional Error VIN = 1 mV rms VIN = 10 mV rms VIN = 100 mV rms VIN = 200 mV rms ±3 dB Bandwidth VIN = 1 mV rms VIN = 10 mV rms VIN = 100 mV rms VIN = 200 mV rms Low Impedance Input (Pin 1) for 1% Additional Error VIN = 1 mV rms VIN = 10 mV rms VIN = 100 mV rms VIN = 200 mV rms ±3 dB Bandwidth VIN = 1 mV rms VIN = 10 mV rms VIN = 100 mV rms VIN = 200 mV rms POWER SUPPLY Operating Voltage Range Min VS = ±16.5 V VS = ±16.5 V 0 to 1.6 0 to 3.6 0 to 4 0 to 4 2 @ dc AD736K/AD736B Min Typ Max ±0.5 ±0.5 20 130 1.7 ±0.1 1 50 50 0 to 1.6 0 to 3.6 0 to 4 0 to 4 2 3.8 5 12 ±0.3 ±0.3 20 130 Unit mV mV µV/°C µV/V µV/V 1.7 V 3.8 V 5 12 3 0.2 3 0.2 V V mA mA Ω 1 6 37 33 1 6 37 33 kHz kHz kHz kHz 5 55 170 190 5 55 170 190 kHz kHz kHz kHz 1 6 90 90 1 6 90 90 kHz kHz kHz kHz 5 55 350 460 5 55 350 460 kHz kHz kHz kHz Sine wave input Sine wave input Sine wave input Sine wave input +2.8, −3.2 Zero signal Sine wave input 0°C to 70°C −40°C to +85°C ±5 ±16.5 160 230 200 270 AD736JN, AD736JR AD736AQ, AD736AR +2.8, −3.2 ±5 ±16.5 V 160 230 200 270 µA µA AD736KN, AD736KR AD736BQ, AD736BR Accuracy is specified with the AD736 connected as shown in Figure 18 with Capacitor CC. Nonlinearity is defined as the maximum deviation (in percent error) from a straight line connecting the readings at 0 mV rms and 200 mV rms. Output offset voltage is adjusted to zero. Error vs. crest factor is specified as additional error for a 200 mV rms signal. Crest factor = VPEAK/V rms. 4 DC offset does not limit ac resolution. 1 2 3 Rev. I | Page 4 of 20 Data Sheet AD736 ABSOLUTE MAXIMUM RATINGS THERMAL RESISTANCE Table 2. Parameter Supply Voltage Internal Power Dissipation Input Voltage Pin 2 through Pin 8 Pin 1 Output Short-Circuit Duration Differential Input Voltage Storage Temperature Range (Q) Storage Temperature Range (N, R) Lead Temperature (Soldering, 60 sec) ESD Rating θJA 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 Table 3. Thermal Resistance ±VS ±12 V Indefinite +VS and –VS –65°C to +150°C –65°C to +125°C 300°C 500 V Package Type 8-Lead PDIP 8-Lead CERDIP 8-Lead SOIC 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. I | Page 5 of 20 θJA 165 110 155 Unit °C/W °C/W °C/W AD736 Data Sheet PIN CONFIGURATION AND FUNCTION DESCRIPTIONS 8 AD736 COM +VS TOP VIEW CF 3 (Not to Scale) 6 OUTPUT –VS 4 7 5 CAV 00834-025 CC 1 VIN 2 Figure 2. Pin Configuration Table 4. Pin Function Descriptions Pin No. 1 Mnemonic CC 2 3 4 5 6 7 8 VIN CF −VS CAV OUTPUT +VS COM Description Coupling Capacitor. If dc coupling is desired at Pin 2, connect a coupling capacitor to this pin. If the coupling at Pin 2 is ac, connect this pin to ground. Note that this pin is also an input, with an input impedance of 8 kΩ. Such an input is useful for applications with high input voltages and low supply voltages. High Input Impedance Pin. Connect an Auxiliary Low-Pass Filter Capacitor from the Output. Negative Supply Voltage if Dual Supplies Are Used, or Ground if Connected to a Single-Supply Source. Connect the Averaging Capacitor Here. DC Output Voltage. Positive Supply Voltage. Common. Rev. I | Page 6 of 20 Data Sheet AD736 TYPICAL PERFORMANCE CHARACTERISTICS 10V SINE WAVE INPUT, VS = ±5V, CAV = 22µF, CF = 4.7µF, CC = 22µF VIN = 200mV rms 1kHz SINE WAVE CAV = 100µF CF = 22µF 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 16 100µV 0.1 Figure 3. Additional Error vs. Supply Voltage 10 –3dB FREQUENCY (kHz) 1000 10V SINE WAVE INPUT, VS = ±5V, CAV = 22µF, CF = 4.7µF, CC = 22µF DC-COUPLED 14 1V INPUT LEVEL (rms) 12 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 16 100µV 0.1 00834-003 0 Figure 4. Maximum Input Level vs. Supply Voltage 1 10 –3dB FREQUENCY (kHz) 100 00834-006 –3dB 2 1000 Figure 7. Frequency Response Driving Pin 2 6 16 1kHz SINE WAVE INPUT ADDITIONAL ERROR (% of Reading) 14 12 10 8 6 4 2 3ms BURST OF 1kHz = 3 CYCLES 200mV rms SIGNAL VS = ±5V CC = 22µF CF = 100µF 5 4 CAV = 10µF CAV = 33µF 3 2 1 CAV = 100µF 0 0 2 4 6 8 10 SUPPLY VOLTAGE (±V) 12 14 16 0 Figure 5. Peak Buffer Output vs. Supply Voltage 1 2 3 4 CREST FACTOR (VPEAK /V rms) 5 00834-007 CAV = 250µF 00834-004 PEAK BUFFER OUTPUT (V) 100 Figure 6. Frequency Response Driving Pin 1 16 PEAK INPUT BEFORE CLIPPING (V) 1 00834-005 –0.5 10% ERROR 00834-002 ADDITIONAL ERROR (% of Reading) 0.7 Figure 8. Additional Error vs. Crest Factor with Various Values of CAV Rev. I | Page 7 of 20 AD736 1.0 VIN = 200mV rms 1kHz SINE WAVE CAV = 100µF CF = 22µF VS = ±5V ERROR (% of Reading) 0.4 0.5 0.2 0 –0.2 –0.4 0 –0.5 –1.0 –1.5 VIN = SINE WAVE @ 1kHz CAV = 22µF, CC = 47µF, CF = 4.7µF, VS = ±5V –2.0 –0.6 –0.8 –60 –40 –20 0 20 60 80 40 TEMPERATURE (°C) 100 120 140 –2.5 10mV Figure 9. Additional Error vs. Temperature 2V Figure 12. Error vs. RMS Input Voltage (Pin 2), Output Buffer Offset Is Adjusted to Zero 600 100 VIN = 200mV rms CC = 47µF CF = 47µF VS = ±5V VIN = 200mV rms 1kHz SINE WAVE CAV = 100µF CF = 22µF VS = ±5V 500 400 CAV (µF) DC SUPPLY CURRENT (µA) 1V 100mV INPUT LEVEL (rms) 00834-011 0.6 00834-008 ADDITIONAL ERROR (% of Reading) 0.8 Data Sheet 300 10 –0.5% 200 0 0.2 0.6 0.4 rms INPUT LEVEL (V) 0.8 1.0 1 10 00834-009 100 Figure 10. DC Supply Current vs. rms Input Level 100 FREQUENCY (Hz) Figure 13. CAV vs. Frequency for Specified Averaging Error 10mV 1V VIN = 1kHz SINE WAVE INPUT AC-COUPLED VS = ±5V –0.5% INPUT LEVEL (rms) –1% 1mV 100µV 100mV 10mV 10µV 100 1k 10k –3dB FREQUENCY (Hz) Figure 11. RMS Input Level (Pin 2) vs. −3 dB Frequency 100k 1mV 1 10 100 FREQUENCY (Hz) 1k 00834-013 VIN SINE WAVE AC-COUPLED CAV = 10µF, CC = 47µF, CF = 47µF, VS = ±5V 00834-010 INPUT LEVEL (rms) 1k 00834-012 –1% Figure 14. RMS Input Level vs. Frequency for Specified Averaging Error Rev. I | Page 8 of 20 Data Sheet AD736 10nA 4.0 1nA INPUT BIAS CURRENT 3.0 2.5 2.0 2 4 10 6 8 SUPPLY VOLTAGE (±V) 12 14 16 100fA –55 00834-014 0 Figure 15. Pin 2 Input Bias Current vs. Supply Voltage 1V VS = 5V CC = 22µF CF = 0µF CAV = 100µF CAV = 10µF 10mV CAV = 33µF 10ms 100ms 1s SETTLING TIME 10s 100s 00834-015 1mV 100µV 1ms –35 –15 5 25 65 45 TEMPERATURE (°C) 85 105 Figure 17. Pin 2 Input Bias Current vs. Temperature 100mV INPUT LEVEL (rms) 10pA 1pA 1.5 1.0 100pA Figure 16. RMS Input Level for Various Values of CAV vs. Settling Time Rev. I | Page 9 of 20 125 00834-016 INPUT BIAS CURRENT (pA) 3.5 AD736 Data Sheet THEORY OF OPERATION AC COUPLED CC = 10µF + DC COUPLED FULL-WAVE RECTIFIER AD736 CC COM 8 1 8kΩ 0.1µF OUTPUT AMPLIFIER VIN 2 INPUT AMPLIFIER IB