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AD736AQ-AD736JN-AD736JR-AD736KN-AD736KR
Low Cost, Low Power, True RMS-to-DC Converter
REV.C
Low Cost, Low Power,rue RMS-to-DC Converter
FUNCTIONAL BLOCK DIAGRAMFEATURES
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 1012 V
Low Input Bias Current: 25 pA max
High Accuracy: 60.3 mV 60.3% of Reading
RMS Conversion with Signal Crest Factors Up to 5
Wide Power Supply Range: +2.8 V, –3.2 V to 616.5 V
Low Power: 200 mA 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 DESCRIPTIONThe 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 (1012 Ω) FET input which will directly interface
with high Z input attenuators and a low impedance (8 kΩ) input
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 HIGHLIGHTSThe AD736 is capable of computing the average rectified
value, absolute value or true rms value of various input
signals.Only one external component, an averaging capacitor, is
required for the AD736 to perform true rms measurement.The low power consumption of 1 mW makes the AD736
suitable for many battery powered applications.A high input impedance of 1012 Ω eliminates the need for an
external buffer when interfacing with input attenuators.A low impedance input is available for those applications
requiring up to 300 mV rms input signal operating from low
power supply voltages.
AD736–SPECIFICATIONS
(@ +258C 65 V supplies, ac coupled with 1 kHz sine-wave input applied unless
otherwise noted.)INPUT CHARACTERISTICS
OUTPUT CHARACTERISTICS
FREQUENCY RESPONSE
TEMPERATURE RANGE
NOTESAccuracy is specified with the AD736 connected as shown in Figure 16 with capacitor CC.Nonlinearity is defined as the maximum deviation (in percent error) from a straight line connecting the readings at 0 and 200 mV rms. Output offset voltage is adjusted to zero.Error vs. Crest Factor is specified as additional error for a 200 mV rms signal. C.F. = VPEAK/V rms.DC offset does not limit ac resolution.
Specifications are subject to change without notice.
Specifications shown in boldface are tested on all production units at final electrical test.
Results from those tests are used to calculate outgoing quality levels.
ABSOLUTE MAXIMUM RATINGS1Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .±16.5 V
Internal Power Dissipation2 . . . . . . . . . . . . . . . . . . . . .200 mW
Input Voltage . . . . . . . . . . . . . . . . . . . . . . . ±VS
Output Short-Circuit Duration . . . . . . . . . . . . . . . . .Indefinite
Differential Input Voltage . . . . . . . . . . . . . . . . .. +VS and –VS
Storage Temperature Range (Q) . . . . . . –65°C to +150°C
Storage Temperature Range (N, R) . . . . . –65°C to +125°C
Operating Temperature Range
AD736J/K . . . . . . . . . . . . . . . . . . . . . . . . . . .0°C to +70°C
AD736A/B . . . . . . . . . . . . . . . . . . . . . . . . . .–40°C to +85°C
ORDERING GUIDEAD736KN
AD736JR
AD736KR
AD736AQ
AD736BQ
AD736JR-REEL
AD736JR-REEL-7
PIN CONFIGURATION
8-Pin Mini-DIP (N-8), 8-Pin SOIC (R-8),
8-Pin Cerdip (Q-8)Lead Temperature Range (Soldering 60 sec) . . . . . . . .+300°C
ESD Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .500 V
NOTESStresses above those listed under “Absolute Maximum Ratings” may cause
permanent damage to the device. This is a stress rating only and functional
operation of the device at these or any other conditions above those indicated in the
operational section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect device reliability .8-Pin Plastic Package: θJA = 165°C/W
8-Pin Cerdip Package: θJA = 110°C/W
8-Pin Small Outline Package: θJA = 155°C/W
AD736
–Typical CharacteristicsFigure 2.Maximum Input Level
vs. SupplyVoltage
Figure 5.Frequency Response
Driving Pin 2
Figure 8.DC Supply Current vs.
RMS lnput Level
Figure 1.Additional Error vs.
Supply Voltage
Figure 4.Frequency Response
Driving Pin 1
Figure 7.Additional Error vs.
Temperature
Figure 3.Peak Buffer Output vs.
Supply Voltage
Figure 6.Additional Error vs.
Crest Factor vs. CAV
Figure 9.–3 dB Frequency vs.
RMS Input Level (Pin2)
Figure 10.Error vs. RMS Input
Voltage (Pin 2), Output Buffer Off-
set Is Adjusted To Zero
Figure 13.Pin 2 Input Bias Current
vs. Supply Voltage
CALCULATING SETTLING TIME USING FIGURE 14The graph of Figure 14 may be used to closely approximate the
time required for the AD736 to settle when its input level is re-
duced in amplitude. The net time required for the rms converter
to settle will be the difference between two times extracted from
the graph – the initial time minus the final settling time. As an
example, consider the following conditions: a 33 μF averaging
capacitor, an initial rms input level of 100 mV and a final (re-
duced) input level of 1 mV. From Figure 14, the initial settling
time (where the 100 mV line intersects the 33 μF line) is around
80 ms.
The settling time corresponding to the new or final input level
of 1 mV is approximately 8 seconds. Therefore, the net time for
the circuit to settle to its new value will be 8 seconds minus
80 ms which is 7.92 seconds. Note that, because of the smooth
decay characteristic inherent with a capacitor/diode combina-
tion, this is the total settling time to the final value (i.e., not the
settling time to 1%, 0.1%, etc., of final value). Also, this graph
provides the worst case settling time, since the AD736 will settle
very quickly with increasing input levels.
Figure 11. CAV vs. Frequency for
Specified Averaging Error
Figure 14.Settling Time vs. RMS
Input Level for Various
Values of CAV
Figure 12.RMS Input Level vs.
Frequency for Specified Averag-
ing Error
Figure 15.Pin 2 Input Bias Cur-
rent vs. Temperature
