Higher integration with wider dynamic range and faster settling time
Features and Benefits
True rms value
Average rectified value
- 200 mV full-scale input range (larger inputs with input attenuator)
- Direct interfacing with 3½ digit CMOS analog-to-digital (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
Product DetailsThe 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 computes the rms value of both the ac and dc input voltages, and is ac-coupled by adding an input 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 maintained for input waveforms with crest factors of 1 to 3 and crest factors at 2.5% or less with respect to 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 of up 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.
- Computes average rectified, absolute, or true rms value of a signal regardless of waveform.
- Only one external component, an averaging capacitor, is required for the AD737 to perform true rms measurement.
- The standby power consumption of 125 μW makes the AD737 suitable for battery-powered applications.
Product Lifecycle Not Recommended for New Designs
This designates products ADI does not recommend broadly for new designs.
Evaluation Kits (1)
An evaluation board, AD737-EVALZ, is available for experiments or for becoming familiar with rms-to-dc converters. The board is designed for multipurpose applications. The board is configured for dual supplies with the high impedance input connected and the power-down feature disabled. Please refer to the AD737 data sheet for more information.
Tools & Simulations
ADIsimPE, which is powered by SIMetrix/SIMPLIS, is a circuit simulation suite optimized for the design and development of analog and mixed signal circuits. SIMetrix mode is ideal for the simulation of general non-switching circuits. It provides full Pspice compatibility for use with industry-standard SPICE models. SIMPLIS (SIMulation Piecewise-Linear System) mode simulates the operation of switching circuits with vastly improved robustness, speed, and accuracy compared to standard SPICE. It is particularly useful for switching power supply, PLLs, and ADC/DAC applications.
ADI has always placed the highest emphasis on delivering products that meet the maximum levels of quality and reliability. We achieve this by incorporating quality and reliability checks in every scope of product and process design, and in the manufacturing process as well. "Zero defects" for shipped products is always our goal.
Sample & Buy
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.