Integrated Circuit
True RMS-to-DC Converter
AD536A
Data Sheet
FEATURES
FUNCTIONAL BLOCK DIAGRAM
AD536A
True rms-to-dc conversion
Laser trimmed to high accuracy
0.2% maximum error (AD536AK)
0.5% maximum error (AD536AJ)
Wide response capability
Computes rms of ac and dc signals
450 kHz bandwidth: V rms > 100 mV
2 MHz bandwidth: V rms > 1 V
Signal crest factor of 7 for 1% error
dB output with 60 dB range
ABSOLUTE
VALUE
V
IN
dB
SQUARER/
DIVIDER
COM
+
+V
S
C
AV
CURRENT
MIRROR
25kΩ
R
L
Low power: 1.2 mA quiescent current
Single- or dual-supply operation
Monolithic integrated circuit
I
OUT
BUFFER IN
−55°C to +125°C operation (AD536AS)
BUF
25kΩ
BUFFER
OUT
GENERAL DESCRIPTION
80kΩ
–V
The AD536A is a complete monolithic integrated circuit that
performs true rms-to-dc conversion. It offers performance
comparable or superior to that of hybrid or modular units costing
much more. The AD536A directly computes the true rms value of
any complex input waveform containing ac and dc components.
A crest factor compensation scheme allows measurements with 1%
error at crest factors up to 7. The wide bandwidth of the device
extends the measurement capability to 300 kHz with less than 3 dB
errors for signal levels greater than 100 m V.
S
Figure 1.
The AD536A is available in two accuracy grades (J and K) for
commercial temperature range (0°C to 70°C) applications, and
one grade (S) rated for the −55°C to +125°C extended range.
The AD536AK offers a maximum total error of 2 mV 0.2%
of reading, while the AD536AJ and AD536AS have maximum
errors of 5 mV 0.5% of reading. All three versions are available
in a hermetically sealed 14-lead DIP or a 10-pin TO-100 metal
header package. The AD536AS is also available in a 20-terminal
leadless hermetically sealed ceramic chip carrier.
An important feature of the AD536A, not previously available
in rms converters, is an auxiliary dB output pin. The logarithm
of the rms output signal is brought out to a separate pin to allow
the dB conversion, with a useful dynamic range of 60 dB. Using
an externally supplied reference current, the 0 dB level can be
conveniently set to correspond to any input level from 0.1 V to
2 V rms.
The AD536A computes the true root-mean-square level of a
complex ac (or ac plus dc) input signal and provides an equiva-
lent dc output level. The true rms value of a waveform is a more
useful quantity than the average rectified value because it relates
directly to the power of the signal. The rms value of a statistical
signal also relates to its standard deviation.
The AD536A is laser trimmed to minimize input and output offset
voltage, to optimize positive and negative waveform symmetry
(dc reversal error), and to provide full-scale accuracy at 7 V rms.
As a result, no external trims are required to achieve the rated
unit accuracy.
An external capacitor is required to perform measurements to the
fully specified accuracy. The value of this capacitor determines the
low frequency ac accuracy, ripple amplitude, and settling time.
The input and output pins are fully protected. The input circuitry
can take overload voltages well beyond the supply levels. Loss of
supply voltage with the input connected to external circuitry does
not cause the device to fail. The output is short-circuit protected.
The AD536A operates equally well from split supplies or a
single supply with total supply levels from 5 V to 36 V. With
1 mA quiescent supply current, the device is well suited for a
wide variety of remote controllers and battery-powered
instruments.
Rev. E
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
rightsof third parties that may result fromits 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 andregisteredtrademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113 ©1976–2012 Analog Devices, Inc. All rights reserved.
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