AD736

The AD736 is a low power, precision, monolithic true rms-to-dc converter. It is laser trimmed to provide a maximum rror of ±0.3 mV ±0.3% of reading with sine-wave inputs. Fur-thermore, 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 applica-tions. Compared to these circuits, the AD736 offers higher ac-curacy at equal or lower cost.

The AD736 can compute the rms value of both ac and dc input voltages. It can also be operated ac coupled by adding one ex-ternal capacitor. In this mode, the AD736 can resolve input sig-nal levels of 100 V 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 AD736 has its own output buffer amplifier, thereby provid-ing a great deal of design flexibility. Requiring only 200 A of power supply current, the AD736 is optimized for use in por-
table multimeters and other battery powered applications.

The AD736 allows the choice of two signal input terminals: a12 high impedance (10 ?) FET input which will directly interface with high Z input attenuators and a low impedance (8 k?) inputwhich allows the measurement of 300 mV input levels, while operating from the minimum power supply voltage of +2.8 V,3.2 V. The two inputs may be used either singly or differentially.

The AD736 achieves a 1% of reading error bandwidth exceeding 10 kHz for input amplitudes from 20 mV rms to 200 mV rms while consuming only 1 mW.The AD736 is available in four performance grades. The AD736J and AD736K grades are rated over the commercial tem-perature range of 0°C to +70°C. The AD736A and AD736B grades are rated over the industrial temperature range of 40°C to +85°C.The AD736 is available in three low-cost, 8-pin packages: plastic mini-DIP, plastic SO and hermetic cerdip.