AD737: Low Cost, Low Power, True RMS-to-DC Converter
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 ...More
AD737: Low Cost, Low Power, True RMS-to-DC Converter
Product Description
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 occurring at the output, which makes the device highly compatible with high input impedance ADCs.
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 that reduces the power-supply standby current to less than 30 μA.
Two signal input terminals are provided in the AD737. A high impedance (1012 Ω) FET input interfaces directly with high R input attenuators, and a low impedance (8 kΩ) 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 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.
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 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 −40°C to +85°C. The AD737 is available in three low cost, 8lead packages: PDIP, SOIC_N, and CERDIP.
Product Highlights
- 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.
Features
- Computes
True rms value
Average rectified value
Absolute value - 200 mV full-scale input range (larger inputs with input attenuator)
- Direct interfacing with 3½ digit CMOS ADCs
- High input impedance: 1012 Ω
- 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 μA maximum supply current
- No external trims needed for specified accuracy
- A general-purpose, buffered voltage output version also available (AD736)
Diagrams
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- Other Diagrams
- Symbols and Footprints
Functional Block Diagram for AD737
Low Cost, Low Power, True RMS-to-DC Converter
Other Diagrams for AD737
Low Cost, Low Power, True RMS-to-DC Converter
AD737 Pin Configurations
Functional Block Diagram for AD737
| Part# | Total Error (@ 25°C) | BW (kHz@ 100mV) | Supply Voltage | Max Input Level (Vrms) | dB Output (Y/N) | Supply Current (max) | Error (%@ CF = 3) | Error %@ CF = As Shown | Temp Range (°C) | Package | Price* (1000-4999) |
|---|---|---|---|---|---|---|---|---|---|---|---|
| AD536A | +/-2+/-0.2 (mV) | 450 | +/-15 | 7 | Y | 2 | 0.1 | -1.0 (@CF =7) | -55 to 125 | CDIP, HEADER, LCC, DIE | $7.87 |
| AD636 | +/-0.2+/-0.5 (mV) | 1500 | +3/-5 | 8.5 | Y | 1 | 0.2 | -0.5 (@CF =6) | -55 to 125 | CDIP, HEADER, DIE | $6.18 |
| AD637 | +/-0.5+/-0.2 (mV) | 8000 | +3/-5 | 10.6 | Y | 3 | +/-0.1 | ±1 (@CF =10) | -55 to 125 | SOIC, CDIP, HEADER, DIE | $11.01 |
| AD736 | +/-0.2+/-0.3 (mV) | 33 | +2.8/-3.2 | 1 | N | 0.2 | 0.7 | ±2.5 (@CF =5) | -40 to 85 | SOIC, CDIP, PDIP | $4.21 |
| AD737 | +/-0.2+/-0.3 (mV) | 33 | +/-2.5 | 1 | N | 0.16 | 0.7 | ±2.5 (@CF =5) | -40 to 85 | SOIC, CDIP, PDIP | $3.35 |
* The pricing listed here is provided only for budgetary purposes as recommended list price in U.S.
Dollars in the United States ex factor per unit for the stated volume. Pricing displayed for Evaluation Boards and Kits is based on 1-piece pricing.
** Pricing is currently unavailable. Click on the product number to see the Product Page for additional information.