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AD737:  Low Cost, Low Power, True RMS-to-DC Converter

Product Details


Newer Alternatives:
  • AD8436 with fast settling time, wider dynamic range, embedded input/output low bias current buffer in a smaller package.

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. In power-down mode, the standby supply current in is typically 25 μA.

The AD737 has both high (1012 Ω) and low impedance input options. The high-Z FET input connects high source impedance 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 two performance grades. The AD737J and AD737K grades operate 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 grade operates over the industrial temperature range of −40°C to +85°C. The AD737 is available in two low cost, 8-lead packages: PDIP and SOIC_N.

Product Highlights

  1. Computes average rectified, absolute, or true rms value of a signal regardless of waveform.
  2. Only one external component, an averaging capacitor, is required for the AD737 to perform true rms measurement.
  3. The standby power consumption of 125 μW makes the AD737 suitable for battery-powered applications.

FEATURES and BENEFITS

  • 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: ±2.8 V, −3.2 V to ±16.5 V
  • Low power: 25 μA (typical) standby current
  • No external trims needed for specified accuracy
  • The AD737 output is negative-going; the AD736 is a positive output-going version of the same basic device

Functional Block Diagram for AD737

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Documentation

Title Content Type File Type
AD737: Low Cost, Low Power, True RMS-to-DC Converter Data Sheet  (Rev I, 06/2012) (pdf, 612 kB) Data Sheets PDF
AN-653: Improving Temperature, Stability, and Linearity of High Dynamic Range RMS RF Power Detectors  (pdf, 415 kB) Application Notes PDF
AN-268: RMS-to-DC Converters Ease Measurement Tasks  (pdf, 638 kB)
RMS-to-DC Converters compute the true RMS value of a signal without regard to waveform shape.
Application Notes PDF
RMS-to-DC Application Guide Second Edition Design Handbooks HTML
Introduction to Analog RMS-to-DC Technology: Converters and Applications Online Training Modules HTML
RAQs index Rarely Asked Questions HTML
Glossary of EE Terms Glossary HTML

Design Tools,Models,Drivers & Software

Title Content Type File Type
AD737 SPICE Macro-Model SPICE Models HTML

Evaluation Kits & Symbols & Footprints

Symbols and Footprints— Analog Devices offers Symbols & Footprints which are compatible with a large set of today’s CAD systems for broader and easier support.

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Price, packaging, availability

AD737 Model Options
Model Package Pins Temp.
Range
Packing,
Qty
Price*(100-499) Price*1000 pcs RoHS View PCN/ PDN Check Inventory/
Purchase/Sample
AD737ANZ Status: Production 8 ld PDIP 8 Ind Tube, 50 $8.42 $8.42 Y  Material Info PCN/PDN Purchase
AD737ARZ Status: Production 8 ld SOIC 8 Ind Tube, 98 $8.85 $8.85 Y  Material Info Notify Me Purchase
AD737JNZ Status: Production 8 ld PDIP 8 Comm. Tube, 50 $3.96 $3.59 Y  Material Info PCN Purchase
AD737JRZ Status: Production 8 ld SOIC 8 Comm. Tube, 98 $3.77 $3.42 Y  Material Info Notify Me Purchase
AD737JRZ-5 Status: Production 8 ld SOIC 8 Comm. Tube, 98 $3.77 $3.42 Y  Material Info Notify Me Purchase
AD737JRZ-5-R7 Status: Production 8 ld SOIC 8 Comm. Reel, 1000 - $3.42 Y  Material Info Notify Me Purchase
AD737JRZ-5-RL Status: Production 8 ld SOIC 8 Comm. Reel, 2500 - $3.42 Y  Material Info Notify Me Purchase
AD737JRZ-R7 Status: Production 8 ld SOIC 8 Comm. Reel, 1000 - $3.42 Y  Material Info Notify Me Purchase
AD737JRZ-RL Status: Production 8 ld SOIC 8 Comm. Reel, 2500 - $3.42 Y  Material Info Notify Me Purchase
AD737KR-REEL Status: Production 8 ld SOIC 8 Comm. Reel, 2500 - $10.28 N  Material Info PDN Purchase
AD737KR-REEL7 Status: Production 8 ld SOIC 8 Comm. Reel, 1000 - $10.28 N  Material Info PDN Purchase
AD737KRZ-R7 Status: Production 8 ld SOIC 8 Comm. Reel, 1000 - $8.56 Y  Material Info Notify Me Purchase
AD737KRZ-RL Status: Production 8 ld SOIC 8 Comm. Reel, 2500 - $8.56 Y  Material Info PDN Purchase
Price Table Help

The USA list pricing shown is for BUDGETARY USE ONLY, shown in United States dollars (FOB USA per unit for the stated volume), and is subject to change. International prices may differ due to local duties, taxes, fees and exchange rates. For volume-specific price or delivery quotes, please contact your local Analog Devices, Inc. sales office or authorized distributor. Pricing displayed for Evaluation Boards and Kits is based on 1-piece pricing.


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