Analog Devices AD736 Datasheet

Low Cost, Low Power,

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
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 DESCRIPTION

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. 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 AD736 offers higher ac­curacy 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 ex­ternal capacitor. In this mode, the AD736 can resolve input sig­nal 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 provid­ing a great deal of design flexibility. Requiring only 200 µA of
power supply current, the AD736 is optimized for use in por­table multimeters and other battery powered applications.

The AD736 allows the choice of two signal input terminals: a
high impedance (10
with high Z input attenuators and a low impedance (8 kΩ) input

12

Ω) FET input which will directly interface

12

V

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 tem­perature 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

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
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.

12

Ω eliminates the need for an

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: [phone] Fax: [phone]

(@ +258C 65 V supplies, ac coupled with 1 kHz sine-wave input applied unless

AD736–SPECIFICA TIONS

Model Conditions Min Typ Max Min Typ Max Units

TRANSFER FUNCTION
CONVERSION ACCURACY 1 kHz Sine Wave

Total Error, Internal Trim

All Grades 0–200 mV rms 0.3/0.3 0.5/0.5 0.2/0.2 0.3/0.3 ±mV/±% of Reading
T

MIN–TMAX

A&B Grades @ 200 mV rms 0.7/0.7 0.5/0.5 ±mV/±% of Reading
J&K Grades @ 200 mV rms 0.007 0.007 ±% of Reading/°C

vs. Supply Voltage

@ 200 mV rms Input V

@ 200 mV rms Input V
dc Reversal Error, dc Coupled @ 600 mV dc 1.3 2.5 1.3 2.5 % of Reading
Nonlinearity

2

, 0 mV–200 mV @ 100 mV rms 0 +0.25 +0.35 0 +0.25 +0.35 % of Reading

Total Error, External Trim 0–200 mV rms 0.1/0.5 0.1/0.3 ±mV/±% of Reading

ERROR vs. CREST FACTOR

Crest Factor 1 to 3 CAV, CF = 100 µF 0.7 0.7 % Additional Error
Crest Factor = 5 CAV, CF = 100 µF 2.5 2.5 % Additional Error

INPUT CHARACTERISTICS

High Impedance Input (Pin 2)

Signal Range

Continuous rms Level V
Continuous rms Level V
Peak Transient Input V
Peak Transient Input V
Peak Transient Input V
Input Resistance 10
Input Bias Current V

Low Impedance Input (Pin 1)

Signal Range

Continuous rms Level V
Continuous rms Level V
Peak Transient Input V
Peak Transient Input V
Peak Transient Input V
Input Resistance 6.4 8 9.6 6.4 8 9.6 kΩ

Maximum Continuous

Nondestructive Input All Supply Voltages ±12 ±12 V p-p
Input Offset Voltage

J&K Grades 63 63 mV

A&B Grades 63 63 mV

vs. Temperature 8 30 8 30 µV/°C

vs. Supply V

vs. Supply VS = ±5 V to ±3 V 80 80 µV/V

OUTPUT CHARACTERISTICS

Output Offset Voltage

J&K Grades ±0.1 60.5 ±0.1 60.3 mV

A&B Grades 60.5 60.3 mV
vs.Temperature 1 20 1 20 µV/°C
vs. Supply V

Output Voltage Swing

2 kΩ Load V

2 kΩ Load V

2 kΩ Load V

No Load V
Output Current 2 2 mA
Short-Circuit Current 3 3 mA
Output Resistance @ dc 0.2 0.2 Ω

FREQUENCY RESPONSE

High Impedance Input (Pin 2)

For 1% Additional Error Sine-Wave Input

V

= 1 mV rms 1 1 kHz

IN

V

= 10 mV rms 6 6 kHz

IN

V

= 100 mV rms 37 37 kHz

IN

VIN = 200 mV rms 33 33 kHz

1

ac Coupled Using C
200 mV–1 V rms –1.2 62.0 –1.2 62.0 % of Reading

= ±5 V to ±16.5 V 0 +0.06 +0.1 0 +0.06 +0.1 %/V

S

= ±5 V to ±3 V 0 –0.18 –0.3 0 –0.18 –0.3 %/V

S

3

= +2.8 V, –3.2 V 200 200 mV rms

S

= ±5 V to ±16.5 V 11V rms

S

= +2.8 V, –3.2 V 60.9 60.9 V

S

= ±5 V ±2.7 ±2.7 V

S

= ±16.5 V 64.0 64.0 V

S

= ±3 V to ±16.5 V 1 25 1 25 pA

S

= +2.8 V, –3.2 V 300 300 mV rms

S

= ±5 V to ±16.5 V l l V rms

S

= +2.8 V, –3.2 V ±1.7 ±1.7 V

S

= ±5 V ±3.8 ±3.8 V

S

= ±16.5 V ±11 ±11 V

S

4

ac Coupled

= ±5 V to ±16.5 V 50 150 50 150 µV/V

S

= ±5 V to ±16.5 V 50 130 50 130 µV/V

S

V

= ±5 V to ±3 V 50 50 µV/V

S

= +2.8 V, –3.2 V 0 to +1.6 +1.7 0 to +1.6 +1.7 V

S

= ±5 V 0 to +3.6 +3.8 0 to +3.6 +3.8 V

S

= ±16.5 V 0 to +4 +5 0 to +4 +5 V

S

= ±16.5 V 0 to +4 +12 0 to +4 +12 V

S

otherwise noted.)

AD736J/A AD736K/B

V

= Avg.(V

OUT

C

2

)

IN

12

V

OUT

= Avg.(V

10

2

)

IN

12

Ω

–2–

REV. C

AD736

AD736J/A AD736K/B

Model Conditions Min Typ Max Min Typ Max Units

±3 dB Bandwidth Sine-Wave Input

= 1 mV rms 5 5 kHz

V

IN

V

= 10 mV rms 55 55 kHz

IN

V

= 100 mV rms 170 170 kHz

IN

VIN = 200 mV rms 190 190 kHz

FREQUENCY RESPONSE

Low Impedance Input (Pin 1)

For 1% Additional Error Sine-Wave Input

V

= 1 mV rms 1 1 kHz

IN

V

= 10 mV rms 6 6 kHz

IN

V

= 100 mV rms 90 90 kHz

IN

V

= 200 mV rms 90 90 kHz

IN

±3 dB Bandwidth Sine-Wave Input

V

= l mV rms 5 5 kHz

IN

V

= 10 mV rms 55 55 kHz

IN

V

= 100 mV rms 350 350 kHz

IN

VIN = 200 mV rms 460 460 kHz

POWER SUPPLY

OperatingVoltageRange +2.8, –3.2 ±5 ± 16.5 +2.8, –3.2 ±5 ± 16.5 Volts
Quiescent Current Zero Signal 160 200 160 200 µA

200 mV rms, No Load Sine-Wave Input 230 270 230 270 µA

TEMPERATURE RANGE

Operating, Rated Performance

Commercial (0°C to +70°C) AD736J AD736K
Industrial (–40°C to +85°C) AD736A AD736B

NOTES

l

Accuracy is specified with the AD736 connected as shown in Figure 16 with capacitor CC.

2

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.

3

Error vs. Crest Factor is specified as additional error for a 200 mV rms signal. C.F. = V

4

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 RATINGS

Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±16.5 V

Internal Power Dissipation

2

. . . . . . . . . . . . . . . . . . . . .200 mW

1

Input Voltage . . . . . . . . . . . . . . . . . . . . . . . ±V

Output Short-Circuit Duration . . . . . . . . . . . . . . . . . Indefinite

Differential Input Voltage . . . . . . . . . . . . . . . . . . +V

and –V

S

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

/V rms.

PEAK

Lead Temperature Range (Soldering 60 sec) . . . . . . . . +300°C

ESD Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .500 V

NOTES

1

Stresses above those listed under “Absolute Maximum Ratings” may cause

S

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

S

maximum rating conditions for extended periods may affect device reliability .

2

8-Pin Plastic Package: θJA = 165°C/W
8-Pin Cerdip Package: θ
8-Pin Small Outline Package: θJA = 155°C/W

= 110°C/W

JA

ORDERING GUIDE

Temperature Package Package

Model Range Description Option

AD736JN 0°C to +70°C Plastic Mini-DIP N-8

AD736KN 0°C to +70°C Plastic Mini-DIP N-8

AD736JR 0°C to +70°C Plastic SOIC SO-8

AD736KR 0°C to +70°C Plastic SOIC SO-8

AD736AQ –40°C to +85°C Cerdip Q-8

AD736BQ –40°C to +85°C Cerdip Q-8

AD736JR-REEL 0°C to +70°C Plastic SOIC SO-8

AD736JR-REEL-7 0°C to +70°C Plastic SOIC SO-8

AD736KR-REEL 0°C to +70°C Plastic SOIC SO-8

AD736KR-REEL-7 0°C to +70°C Plastic SOIC SO-8

REV. C

PIN CONFIGURATION

8-Pin Mini-DIP (N-8), 8-Pin SOIC (R-8),

8-Pin Cerdip (Q-8)

–3–