Data Sheet
FEATURES
Computes
True rms value
Average rectified value
Absolute value
Provides
200 mV full-scale input range (larger inputs with
input scaling)
Direct interfacing with 3½ digit CMOS ADCs
High input impedance: 10
12
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: ±2.5 V to ±16.5 V
Low power: 25 µA (typical) standby current
No external trims needed for specified accuracy
The
output is negative-going; the
is a positive
output-going version of the same basic device
C
C
Low Cost, Low Power,
True RMS-to-DC Converter
FUNCTIONAL BLOCK DIAGRAM
8kΩ
8kΩ
COM
C
F
ABSOLUTE
VALUE
CIRCUIT
SQUARER
DIVIDER
OUTPUT
V
IN
C
AV
+V
S
POWER
DOWN
BIAS
SECTION
–V
S
C
AV
00828-001
Figure 1.
GENERAL DESCRIPTION
The
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
offers
higher accuracy at equal or lower cost.
The
can compute the rms value of both ac and dc input
voltages. It can also be operated ac-coupled by adding one
external capacitor. In this mode, the
can resolve input
signal levels of 100 µV rms or less, despite variations in tem-
perature 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
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
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.
Rev. I
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 that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.
The
has both high (10
12
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 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
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
is available in two performance grades. The
and
grades operate over the commercial temperature
range of 0°C to 70°C. The
is tested with supply
voltages of ±2.5 V dc. The
grade operates over the
industrial temperature range of −40°C to +85°C. The
is
available in two low cost, 8lead packages: PDIP and SOIC_N.
PRODUCT HIGHLIGHTS
1.
2.
3.
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
to perform true rms measurement.
The standby power consumption of 125 μW makes the
suitable for battery-powered applications.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.461.3113
©2012 Analog Devices, Inc. All rights reserved.
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