Analog Devices Inc. AD636JD

Overview

AD636JD from Analog Devices is a monolithic true RMS-to-DC converter IC designed for precision low-level ac/dc signal measurement in portable and battery-powered instrumentation. It delivers 200 mV full-scale output, ±1.0% maximum total error (J-grade), 1.5 MHz ±3 dB bandwidth at 200 mV rms input, and operates from dual supplies (±2.5 V to ±16.5 V) or single supply (+5 V to +24 V). Its integrated buffer amplifier and IOUT current output support direct interfacing with ADCs and display drivers.

For engineers reviewing the AD636JD datasheet, AD636JD pinout, AD636JD application, or AD636JD equivalent, key selection considerations include its 0.5%–1.0% accuracy grade, crest factor tolerance up to 6, 800 μA quiescent current, dB output with 50 dB range, and compatibility with standard 10 MΩ attenuators via the BUF IN/BUF OUT terminals.

Technical Context

The AD636JD implements an implicit analog RMS computation using an absolute value circuit, squarer/divider, current mirror, and averaging capacitor (CAV) to solve V_OUT = √(avg[V_IN²]). Its architecture avoids digital sampling and preserves analog fidelity for complex waveforms including pulse trains with crest factors ≤6.

It features dual-mode operation: voltage output across RL (10 kΩ internal) or current output (IOUT = 100 μA/V_rms) with 8–12 kΩ output impedance; a dedicated dB output derived from the emitter of Q3 provides logarithmic scaling (−3.0 mV/dB) with externally set 0 dB reference (1–50 μA IREF).

Key Specifications

Pinout & Package

AD636JD is supplied in a 14-lead hermetically sealed SBDIP (Small Outline Ceramic DIP) package with 0.300" wide body and 0.100" lead pitch. Pin 1 is marked with a dot; pins 2, 11, 12, and 13 are no-connect (NC). The package is rated for 0°C to +70°C operation and offers robust ESD protection (1000 V HBM).

Key Features

Applications

Equivalent & Alternatives

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

Compared with AD636K, AD636JD trades 0.5% absolute error margin for lower cost and identical form factor; compared with AD736JRZ, it delivers 3× higher bandwidth and superior crest factor handling at the expense of higher quiescent current and larger package - making AD636JD the balanced choice for industrial handheld test equipment.

Availability

AD636JD is available at Aetrix Electronics and suitable for portable multimeters, audio level analyzers, power supply monitors, and battery-powered instrumentation requiring stable component supply and long-term calibration integrity.

Supply support for AD636JD 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, headquartered in Norwood, MA, with design centers worldwide and ISO 9001-certified manufacturing.

The AD636 product line was engineered specifically for precision analog RMS measurement in portable and industrial test equipment, emphasizing low power, wide crest factor tolerance, and factory-trimmed accuracy without external calibration.

FAQ

What is the maximum input signal level the AD636JD can handle without damage?

The AD636JD withstands continuous nondestructive input levels up to ±12 V p-p across all supply voltages, and peak transients up to ±5.0 V p-p with ±5 V supplies. This input overvoltage tolerance applies even when no supply voltage is present, protecting the device during probing errors or hot-plug scenarios. The AD636JD input stage is fully protected per its Absolute Maximum Ratings table, ensuring robustness in field service environments.

Can the AD636JD operate from a single 9 V battery?

Yes, the AD636JD supports single-supply operation from +5 V to +24 V, making it compatible with a fresh 9 V alkaline or lithium battery. When powered from 9 V, the COM pin must be biased using the external R-R-C network shown in Figure 11 of the datasheet to establish an artificial ground reference. This configuration maintains full 200 mV rms input range and preserves the specified ±1.0% accuracy, enabling true RMS functionality in compact handheld meters.

How does the CAV capacitor value affect AD636JD performance?

The CAV capacitor (Pin 4) sets the averaging time constant at 25 ms per microfarad, directly governing low-frequency accuracy, output ripple magnitude, and settling time. For example, a 4 μF CAV yields 1% dc error above 10 Hz but increases 1% settling time to ~460 ms for decreasing signals. Larger CAV reduces ripple but slows response; post-filtering (e.g., 2-pole active filter) allows smaller CAV while maintaining low ripple - a key trade-off in dynamic measurement applications using the AD636JD.

Does the AD636JD require external trimming to achieve datasheet accuracy?

No, the AD636JD is laser-trimmed at wafer level for input/output offset, positive/negative waveform symmetry, and full-scale accuracy at 200 mV rms, so no external trims are needed to meet its ±0.5 mV ± 1.0% total error specification. Optional external trims (R1, R4 in Figure 10) exist only for applications demanding sub-0.5% error - the AD636JD delivers full-rated accuracy out-of-the-box, simplifying production calibration for portable test instruments.

What is the purpose of the IOUT pin on the AD636JD?

The IOUT pin (Pin 8) provides a true RMS current output scaled at 100 μA per volt rms of input, with ±20% tolerance and 8–12 kΩ output impedance. This ratiometric current output enables noise-immune transmission over cables, direct interfacing with current-input ADCs or optocouplers, and isolation in high-common-mode-voltage applications. Unlike the buffered voltage output (BUF OUT), IOUT remains functional even when the internal buffer is reconfigured for input use - enhancing design flexibility in the AD636JD.