True RMS-to-DC Converter
True RMS-to-DC Conversion
Laser-Trimmed to High Accuracy
0.2% Max Error (AD536AK)
0.5% Max 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
Low Power: 1.2 mA Quiescent Current
Single or Dual Supply Operation
Monolithic Integrated Circuit
–55؇C to +125؇C Operation (AD536AS)
The AD536A is a complete monolithic integrated circuit which
performs true rms-to-dc conversion. It offers performance which
is 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. It has a crest factor compensation scheme which
allows measurements with 1% error at crest factors up to 7. The
wide bandwidth of the device extends the measurement capabi-
lity to 300 kHz with 3 dB error for signal levels above 100 mV.
An important feature of the AD536A not previously available in
rms converters is an auxiliary dB output. 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 con-
veniently set by the user to correspond to any input level from
0.1 to 2 volts rms.
The AD536A is laser trimmed at the wafer level for input and
output offset, positive and negative waveform symmetry (dc re-
versal error), and full-scale accuracy at 7 V rms. As a result, no
external trims are required to achieve the rated unit accuracy.
There is full protection for both inputs and outputs. The input
circuitry can take overload voltages well beyond the supply lev-
els. Loss of supply voltage with inputs connected will not cause
unit failure. The output is short-circuit protected.
The AD536A is available in two accuracy grades (J, K) for com-
mercial 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, and the AD536AJ and AD536AS have maximum errors
of ± 5 mV ± 0.5% of reading. All three versions are available in
either a hermetically sealed 14-lead DIP or 10-pin TO-100
metal can. The AD536AS is also available in a 20-leadless her-
metically sealed ceramic chip carrier.
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.
PIN CONFIGURATIONS AND
FUNCTIONAL BLOCK DIAGRAMS
TO-116 (D-14) and
NC 2 AD536A
25k⍀ 9 RL
NC = NO CONNECT
LCC (E-20A) Package
NC VIN NC +VS NC
3 2 1 20 19
9 10 11 12 13
BUF BUF NC IOUT RL
NC = NO CONNECT
1. The AD536A computes the true root-mean-square level of a
complex ac (or ac plus dc) input signal and gives an equiva-
lent dc output level. The true rms value of a waveform is a
more useful quantity than the average rectified value since it
relates directly to the power of the signal. The rms value of a
statistical signal also relates to its standard deviation.
2. The crest factor of a waveform is the ratio of the peak signal
swing to the rms value. The crest factor compensation
scheme of the AD536A allows measurement of highly com-
plex signals with wide dynamic range.
3. The only external component required to perform measure-
ments to the fully specified accuracy is the capacitor which
sets the averaging period. The value of this capacitor determines
the low frequency ac accuracy, ripple level and settling time.
4. The AD536A will operate equally well from split supplies or
a single supply with total supply levels from 5 to 36 volts.
The one milliampere quiescent supply current makes the
device well-suited for a wide variety of remote controllers and
battery powered instruments.
5. The AD536A directly replaces the AD536 and provides im-
proved bandwidth and temperature drift specifications.
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© Analog Devices, Inc., 1999