a
FEATURES
COMPUTES
True RMS Value
Average Rectified Value
Absolute Value
PROVIDES
200 mV Full-Scale Input Range
(Larger Inputs with Input Attenuator)
High Input Impedance of 10
12
Low Input Bias Current: 25 pA max
High Accuracy: 0.3 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: 200 A max Supply Current
Buffered Voltage Output
No External Trims Needed for Specified Accuracy
AD737—An Unbuffered Voltage Output Version with
Chip Power Down Is Also Available
PRODUCT DESCRIPTION
Low Cost, Low Power,
True RMS-to-DC Converter
AD736
FUNCTIONAL BLOCK DIAGRAM
which 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.
PRODUCT HIGHLIGHTS
The AD736 is a low power, precision, monolithic true
rms-to-dc converter. It is laser trimmed to provide a maximum
error 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
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 AD736 has its own output buffer amplifier, thereby provid-
ing a great deal of design flexibility. Requiring only 200
µA
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: a
high impedance (10
12
Ω)
FET input which will directly interface
with high Z input attenuators and a low impedance (8 kΩ) input
1. The AD736 is capable of computing the average rectified
value, absolute value or true rms value of various input
signals.
2. Only one external component, an averaging capacitor, is
required for the AD736 to perform true rms measurement.
3. The low power consumption of 1 mW makes the AD736
suitable for many battery powered applications.
4. A high input impedance of 10
12
Ω
eliminates the need for an
external buffer when interfacing with input attenuators.
5. A low impedance input is available for those applications
requiring up to 300 mV rms input signal operating from low
power supply voltages.
REV. C
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700
Fax: 617/326-8703
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