Analog Devices Inc. AD737KRZ-R7

Overview

AD737KRZ-R7 from Analog Devices is a monolithic, low-power true RMS-to-DC converter IC designed for precision ac/dc voltage measurement in portable and battery-powered instrumentation. It computes true RMS, average rectified, and absolute values of input signals with ±0.2 mV ± 0.3% reading accuracy, 10¹² Ω high-Z FET input impedance, and 25 µA typical standby current. It operates from ±2.5 V to ±16.5 V dual supplies and delivers negative-going DC output suitable for interfacing with 3½-digit CMOS ADCs in handheld multimeters.

For engineers reviewing the AD737KRZ-R7 datasheet, AD737KRZ-R7 pinout, AD737KRZ-R7 application, or AD737KRZ-R7 equivalent, key selection considerations include its dual-input architecture (Pin 1 low-Z, Pin 2 high-Z), required external averaging capacitor (CAV), crest factor tolerance up to 5, absence of output buffer amplifier, and power-down capability via Pin 3 - all critical for low-offset, low-power RMS measurement systems.

Technical Context

The AD737KRZ-R7 implements a four-stage analog signal path: FET-input amplifier, full-wave precision rectifier, rms core (squaring–averaging–square-rooting), and bias-controlled power-down section. Its rms core relies on an external averaging capacitor (CAV) to set time constant and accuracy, while internal 8 kΩ scaling resistor enables direct low-Z input at Pin 1 and supports quasi-differential operation.

It supports both ac-coupled (via CC capacitor) and dc-coupled configurations, achieves ≤1% reading error bandwidth exceeding 10 kHz at 20–200 mV rms inputs, and maintains ±0.3% reading accuracy across crest factors 1–5 when CAV ≥ 33 µF - enabling reliable measurement of non-sinusoidal waveforms including triac-phase-controlled and pulse-train signals.

Key Specifications

Pinout & Package

AD737KRZ-R7 is housed in an 8-lead SOIC_N (R-8) package, 3.9 mm × 4.9 mm, with standard gull-wing leads and 1.27 mm pitch. Thermal resistance θ_JA = 155°C/W.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar true RMS-to-DC conversion applications.

Compared with AD737KRZ-R7, AD736JRZ-R7 offers identical performance with inverted output polarity, while MAX4206ETA+ trades dual-supply flexibility and high-Z input for single-rail simplicity and built-in buffering - making AD737KRZ-R7 optimal for precision, low-power, wide-dynamic-range RMS measurement in portable test gear.

Availability

AD737KRZ-R7 is available at Aetrix Electronics and suitable for handheld multimeters, industrial power analyzers, battery-powered clamp meters, and audio level meters requiring stable component supply and long-lifecycle availability.

Supply support for AD737KRZ-R7 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Analog Devices, Inc. is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, founded in 1965 and headquartered in Wilmington, MA.

The AD737 belongs to Analog Devices' precision RMS-to-DC converter product line, engineered specifically for high-accuracy, low-power ac voltage measurement in portable instrumentation and industrial monitoring systems where waveform independence and minimal external components are essential.

FAQ

What is the function of Pin 3 (POWER DOWN) on the AD737KRZ-R7?

Pin 3 controls the power-down mode of the AD737KRZ-R7. When pulled high (to +VS), it disables the internal circuitry and reduces supply current to 25 µA typical. When grounded or held low, the AD737KRZ-R7 operates normally with 160 µA typical supply current. This feature is essential for extending battery life in portable instruments where RMS measurement is performed intermittently.

Does the AD737KRZ-R7 require external trimming for specified accuracy?

No, the AD737KRZ-R7 does not require external trims to achieve its specified accuracy of ±0.2 mV ± 0.3% of reading. It is laser-trimmed at wafer level to meet this specification with only one external component - the averaging capacitor CAV. External trims (e.g., scale factor or offset) are optional and only used when higher accuracy than the base specification is required.

Can the AD737KRZ-R7 measure DC signals, and how is DC coupling implemented?

Yes, the AD737KRZ-R7 measures both AC and DC input voltages. For DC coupling, the input signal is applied directly to Pin 2 (VIN) or Pin 1 (CC), with COM serving as the reference. The device computes the true RMS value of the combined AC+DC signal. In DC-coupled mode, input offset voltage is ±31 mV (typical), and the output reflects the RMS magnitude of the total input, including any DC component.

What is the role of the CAV capacitor in the AD737KRZ-R7 circuit?

The CAV capacitor is the critical external component that sets the averaging time constant for true RMS computation in the AD737KRZ-R7. Connected between Pin 5 and COM, it determines both measurement accuracy (especially at low frequencies) and settling time. For example, a 33 µF CAV yields ≤0.35% nonlinearity at 100 mV rms and ~360 ms settling time for 1% accuracy - balancing speed and precision per application requirements.

How does the AD737KRZ-R7 differ from the AD736 in terms of output polarity and compatibility?

The AD737KRZ-R7 provides a negative-going DC output voltage, whereas the AD736 is its functional counterpart with positive-going output. Both share identical accuracy, bandwidth, power consumption, pinout, and package. They are not pin-compatible replacements due to opposite polarity - substituting one for the other requires inverting the output signal path or redesigning downstream interface circuitry.