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AD737BQ

AD737BQ

  • 厂商:

    AD(亚德诺)

  • 封装:

  • 描述:

    AD737BQ - Low Cost, Low Power, True RMS-to-DC Converter - Analog Devices

  • 数据手册
  • 价格&库存
AD737BQ 数据手册
a FEATURES COMPUTES True RMS Value Average Rectified Value Absolute Value PROVIDES 200 mV Full-Scale Input Range (Larger Inputs with Input Attenuator) Direct Interfacing with 3 1/2 Digit CMOS A/D Converters High Input Impedance of 1012 Low Input Bias Current: 25 pA max High Accuracy: 0.2 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: 160 A max Supply Current No External Trims Needed for Specified Accuracy AD736—A General Purpose, Buffered Voltage Output Version Also Available PRODUCT DESCRIPTION Low Cost, Low Power, True RMS-to-DC Converter AD737* FUNCTIONAL BLOCK DIAGRAM 8k CC 1 FULL WAVE RECTIFIER INPUT AMPLIFIER BIAS SECTION RMS CORE AD737 8 COM VIN 2 8k 7 +VS POWER DOWN 3 6 OUTPUT –VS 4 5 CAV The AD737 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 non-rms “precision rectifiers” in many applications. Compared to these circuits, the AD737 offers higher accuracy at equal or lower cost. 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 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 (while introducing only 2.5% additional error) at the 200 mV full-scale input level. The AD737 has no output buffer amplifier, thereby significantly reducing dc offset errors occuring at the output. This allows the device to be highly compatible with high input impedance A/D converters. Requiring only 160 µA of power supply current, the AD737 is optimized for use in portable multimeters and other battery powered applications. This converter also provides a “power down” feature which reduces the power supply standby current to less than 30 µA. *Protected under U.S. Patent Number 5,495,245. The AD737 allows the choice of two signal input terminals: a high impedance (1012 Ω) FET input which will directly interface with high Z input attenuators and a low impedance (8 kΩ) input which 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 may be used either singly or differentially. The AD737 achieves a 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. The AD737 is available in four performance grades. The AD737J and AD737K grades are rated over the commercial temperature range of 0°C to +70°C. The AD737A and AD737B grades are rated over the industrial temperature range of –40°C to +85°C. The AD737 is available in three low-cost, 8-lead packages: plastic DIP, plastic SO and hermetic cerdip. PRODUCT HIGHLIGHTS 1. The AD737 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 AD737 to perform true rms measurement. 3. The low power consumption of 0.72 mW makes the AD737 suitable for many battery powered applications. R EV. C 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 which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 © Analog Devices, Inc., 1999 AD737–SPECIFICATIONS otherwise noted.) Model Conditions Min (@ +25 C, 5 V supplies, ac coupled with 1 kHz sine-wave input applied unless AD737K/B Typ V OUT = 2 AD737J/A Typ Max 2 Min Max Units TRANSFER FUNCTION CONVERSION ACCURACY Total Error, Internal Trim1 All Grades 1 kHz Sine Wave ac Coupled Using C C 0–200 mV rms 200 mV–1 V rms V OUT = Avg .(V IN ) Avg .(V IN ) 0.2/0.3 –1.2 0.007 0 0 0 +0.06 –0.18 1.3 +0.25 0.1/0.2 0.7 2.5 0.4/0.5 2.0 0.5/0.7 0.2/0.2 –1.2 0.007 0.2/0.3 2.0 0.3/0.5 ± mV/± % of Reading % of Reading ± mV/± % of Reading ± % of Reading/° C %/V %/V % of Reading % of Reading ± mV/± % of Reading % Additional Error % Additional Error TMIN-TMAX A&B Grades @ 200 mV rms J&K Grades @ 200 mV rms vs. Supply Voltage @ 200 mV rms Input VS = ± 5 V to ± 16.5 V @ 200 mV rms Input VS = ± 5 V to ± 3 V dc Reversal Error, dc Coupled @ 600 mV dc Nonlinearity2, 0–200 mV @ 100 mV rms Total Error, External Trim 0–200 mV rms ERROR vs. CREST FACTOR3 Crest Factor 1 to 3 CAV , CF = 100 µF Crest Factor = 5 CAV , CF = 100 µF INPUT CHARACTERISTICS High Impedance Input (Pin 2) Signal Range Continuous rms Level VS = +2.8 V, –3.2 V Continuous rms Level VS = ± 5 V to ± 16.5 V Peak Transient Input VS = +2.8 V, –3.2 V Peak Transient Input VS = ± 5 V Peak Transient Input VS = ± 16.5 V Input Resistance Input Bias Current VS = ± 5 V Low Impedance Input (Pin 1) Signal Range Continuous rms Level VS = +2.8 V, –3.2 V Continuous rms Level VS = ± 5 V to ± 16.5 V Peak Transient Input VS = +2.8 V, –3.2 V Peak Transient Input VS = ± 5 V Peak Transient Input VS = ± 16.5 V Input Resistance Maximum Continuous Nondestructive Input All Supply Voltages Input Offset Voltage4 ac Coupled J&K Grades A&B Grades vs. Temperature vs. Supply VS = ± 5 V to ± 16.5 V vs. Supply VS = ± 5 V to ± 3 V OUTPUT CHARACTERISTICS Output Voltage Swing No Load VS = +2.8 V, –3.2 V No Load VS = ± 5 V No Load VS = ± 16.5 V Output Resistance @ dc FREQUENCY RESPONSE High Impedance Input (Pin 2) For 1% Additional Error Sine-Wave Input VIN = 1 mV rms VIN = 10 mV rms VIN = 100 mV rms VIN = 200 mV rms ± 3 dB Bandwidth Sine-Wave Input VIN = 1 mV rms VIN = 10 mV rms VIN = 100 mV rms VIN = 200 mV rms +0.1 –0.3 2.5 +0.35 0 0 0 +0.06 –0.18 1.3 +0.25 0.1/0.2 0.7 2.5 +0.1 –0.3 2.5 +0.35 200 1 0.9 4.0 1012 1 25 ± 2.7 0.9 4.0 1012 1 ± 2.7 200 1 25 mV rms V rms V V V Ω pA 6.4 ± 1.7 ± 3.8 ± 11 8 300 l 9.6 ± 12 3 3 30 150 6.4 ± 1.7 ± 3.8 ± 11 8 300 l 9.6 ± 12 3 3 30 150 mV rms V rms V V V kΩ V p-p mV mV µV/° C µV/V µV/V 8 50 80 8 50 80 0 to –1.6 0 to –3.3 0 to –4 6.4 –1.7 –3.4 –5 8 9.6 0 to –1.6 0 to –3.3 0 to –4 6.4 –1.7 –3.4 –5 8 9.6 V V V kΩ 1 6 37 33 5 55 170 190 1 6 37 33 5 55 170 190 kHz kHz kHz kHz kHz kHz kHz kHz –2– REV. C AD737 Model Conditions Min AD737J/A Typ Max Min AD737K/B Typ Max Units FREQUENCY RESPONSE 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 Quiescent Current VIN = 200 mV rms, No Load Power Down Mode Current TEMPERATURE RANGE Operating, Rated Performance Commercial (0° C to +70°C) Industrial (–40°C to +85 °C) Sine-Wave Input 1 6 90 90 Sine-Wave Input 5 55 350 460 +2.8, –3.2 ± 5 120 170 25 ± 16.5 160 210 40 +2.8, –3.2 5 55 350 460 ±5 120 170 25 ± 16.5 160 210 40 kHz kHz kHz kHz V µA µA µA 1 6 90 90 kHz kHz kHz kHz Zero Signal Sine-Wave Input Pin 3 Tied to +VS AD737J AD737A AD737K AD737B NOTES l Accuracy is specified with the AD737 connected as shown in Figure 16 with capacitor C C. 2 Nonlinearity is defined as the maximum deviation (in percent error) from a straight line connecting the readings at 0 and 200 mV rms. 3 Error vs. Crest Factor is specified as additional error for a 200 mV rms signal. C.F. = V PEAK /V rms. 4 DC offset does not limit ac resolution. Specifications are subject to change without notice. Specifications shown in boldface are tested on all production units at final electrical test. Results from those tests are used to calculate outgoing quality levels. Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ± 16.5 V Internal Power Dissipation2 . . . . . . . . . . . . . . . . . . . . . 200 mW Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Output Short-Circuit Duration . . . . . . . . . . . . . . . . . Indefinite Differential Input Voltage . . . . . . . . . . . . . . . . . . +VS and –VS Storage Temperature Range (Q) . . . . . . –65°C to +150°C Storage Temperature Range (N, R) . . . . . –65°C to +125°C Operating Temperature Range AD737J/K . . . . . . . . . . . . . . . . . . . . . . . . . . . 0°C to +70°C AD737A/B . . . . . . . . . . . . . . . . . . . . . . . . . . –40°C to +85°C Lead Temperature Range (Soldering 60 sec) . . . . . . . . +300 °C ESD Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500 V NOTES 1 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. 2 8-Lead Plastic DIP Package: θ JA = 165°C/W 8-Lead Cerdip Package: θJA = 110°C/W 8-Lead Small Outline Package: θ JA = 155°C/W ABSOLUTE MAXIMUM RATINGS 1 ORDERING GUIDE Temperature Range –40°C to +85°C –40°C to +85°C 0°C to +70°C 0°C to +70°C 0°C to +70°C 0°C to +70°C 0°C to +70°C 0°C to +70°C 0°C to +70°C 0°C to +70°C Package Description Cerdip Cerdip Plastic DIP SOIC 13" Tape and Reel 7" Tape and Reel Plastic DIP SOIC 13" Tape and Reel 7" Tape and Reel Package Option Q-8 Q-8 N-8 SO-8 SO-8 SO-8 N-8 SO-8 SO-8 SO-8 Model AD737AQ AD737BQ AD737JN AD737JR AD737JR-REEL AD737JR-REEL7 AD737KN AD737KR AD737KR-REEL AD737KR-REEL7 PIN CONFIGURATIONS Plastic DIP (N-8), Cerdip (Q-8), SOIC (SO-8) AD737 8 FULL WAVE RECTIFIER INPUT AMPLIFIER BIAS SECTION RMS CORE COM 8k CC 1 VIN 2 8k 7 +VS POWER DOWN 3 6 OUTPUT –VS 4 5 CAV REV. C –3– AD737 –Typical Characteristics Figure 1. Additional Error vs. Supply Voltage Figure 2. Maximum Input Level vs. Supply Voltage Figure 3. Power Down Current vs. Supply Voltage Figure 4. Frequency Response Driving Pin 1 Figure 5. Frequency Response Driving Pin 2 Figure 6. Additional Error vs. Crest Factor vs. CAV Figure 7. Additional Error vs. Temperature Figure 8. DC Supply Current vs. RMS lnput Level Figure 9. 23 dB Frequency vs. RMS Input Level (Pin 2) –4– REV. C Applying the AD737 Figure 10. Error vs. RMS Input Voltage (Pin 2) Using Circuit of Figure 21 Figure 11. C AV vs. Frequency for Specified Averaging Error Figure 12. RMS Input Level vs. Frequency for Specified Averaging Error Figure 13. Pin 2 Input Bias Current vs. Supply Voltage Figure 14. Settling Time vs. RMS Input Level for Various Values of CAV Figure 15. Pin 2 Input Bias Current vs. Temperature CALCULATING SETTLING TIME USING FIGURE 14 TYPES OF AC MEASUREMENT The graph of Figure 14 may 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 will be 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 µF averaging capacitor, an initial rms input level of 100 mV and a final (reduced) input level of 1 mV. From Figure 14, the initial settling time (where the 100 mV line intersects the 33 µF line) is around 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 will be 8 seconds minus 80 ms which is 7.92 seconds. Note that, because of the smooth decay characteristic inherent with a capacitor/diode combination, this is the total settling time to the final value (i.e., not the settling time to 1%, 0.1%, etc., of final value). Also, this graph provides the worst case settling time, since the AD737 will settle very quickly with increasing input levels. The AD737 is capable of measuring ac signals by operating as either an average responding or a true rms-to-de 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 will approximate 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 dc: an ac signal of 1 volt rms will produce the same amount of heat in a resistor as a 1 volt dc signal. REV. C –5– AD737 Table I. Error Introduced by an Average Responding Circuit When Measuring Common Waveforms Waveform Type 1 Volt Peak Amplitude Crest Factor (VPEAK /V rms) True rms Value Average Responding Circuit Calibrated to Read rms Value of Sine Waves Will Read % of Reading Error* Using Average Responding Circuit Undistorted Sine Wave Symmetrical Square Wave Undistorted Triangle Wave Gaussian Noise (98% of Peaks
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