Analog Devices AD736 f Datasheet

Low Cost, Low Power,

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 1012 V
Low input bias current: 25 pA max
High accuracy: ±0.3 mV ±0.3% of reading
RMS conversion with signal crest factors up to 5
Wide power supply range: +2.8 V, –3.2 V to ±16.5 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 also available

GENERAL 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 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 an 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.

Rev. F

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.

True RMS-to-DC Converter

FUNCTIONAL BLOCK DIAGRAM

8kΩ

1

C

C

FULL

WAVE

V

2

IN

AMPLIFIER

C

3

F

–V

S

4

BIAS

SECTION

INPUT

RECTIFIER

RMS CORE

Figure 1.

AD736

8kΩ

OUTPUT

AMPLIFIER

The AD736 allows the choice of two signal input terminals: a
high impedance FET input (10

12

Ω) that directly interfaces with
high Z input attenuators and a low impedance input (8 kΩ) that
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 single-ended or differentially.

The AD736 has a 1% reading error bandwidth that exceeds
10 kHz for the 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 0°C to +70°C
and −20°C to +85°C commercial temperature ranges. The
AD736A and AD736B grades are rated over the −40°C to +85°C
industrial temperature range. The AD736 is available in three
low c ost, 8-lead packages: PDIP, SOIC, and CERDIP.

PRODUCT HIGHLIGHTS

The 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.

12

A high input impedance of 10
external buffer when interfacing with input attenuators.

A low impedance input is available for those applications that
require an input signal up to 300 mV rms operating from low
power supply voltages.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone]
Fax: [phone] © 2004 Analog Devices, Inc. All rights reserved.

www.analog.com

Ω eliminates the need for an

8

7

6

5

AD736

COM

+V

S

OUTPUT

C

AV

00834-F-001

AD736

TABLE OF CONTENTS

Specifications..................................................................................... 3

Absolute Maximum Ratings............................................................ 5

Pin Configuration ........................................................................ 5

ESD Caution.................................................................................. 5

Typical Performance Characteristics ............................................. 6

Rapid Settling Times via the Average Responding

Connection ............................................................................. 11

DC Error, Output Ripple, and Averaging Error..................... 11

AC Measurement Accuracy and Crest Factor........................ 11

Selecting Practical Values for Input Coupling (CC), Averaging

), and Filtering (CF) Capacitors..................................... 11

(C

AV

Calculating Settling Time Using Figure 16............................... 8

Types of AC Measureme nt .......................................................... 9

Theory of Operation ...................................................................... 10

RMS Measurement—Choosing the Optimum

Val u e f o r C

........................................................................... 10

AV

REVISION HISTORY

5/04—Data Sheet Changed from Rev. E to Rev. F.

Changes to Specifications............................................................ 2

Replaced Figure 18 ..................................................................... 10

Updated Outline Dimensions................................................... 16

Changes to Ordering Guide...................................................... 16

4/03—Data Sheet Changed from Rev. D to Rev. E.

Changes to GENERAL DESCRIPTION.................................... 1

Changes to SPECIFICATIONS................................................... 3

Changes to ABSOLUTE MAXIMUM RATINGS.................... 4

Changes to ORDERING GUIDE ............................................... 4

11/02—Data Sheet Changed from Rev. C to Rev. D.

Application Circuits....................................................................... 13

Outline Dimensions....................................................................... 15

Ordering Guide .......................................................................... 16

Changes to FUNCTIONAL BLOCK DIAGRAM.................... 1

Changes to PIN CONFIGURATION ........................................ 3

Figure 1 Replaced ......................................................................... 6

Changes to Figure 2...................................................................... 6

Changes to Application Circuits Figures 4 to 8 ........................ 8

OUTLINE DIMENSIONS updated........................................... 8

Rev. F | Page 2 of 16

AD736

SPECIFICATIONS

Table 1. @25°C ±5 V supplies, ac-coupled with 1 kHz sine wave input applied, unless otherwise noted. Specifications in bold are
tested on all production units at final electrical test. Results from those tests are used to calculate outgoing quality levels.

AD736J/AD736A AD736K/AD736B
Parameter Conditions Min Typ Max Min Typ Max Unit

TRANSFER FUNCTION

= √

V

OUT

CONVERSION ACCURACY 1 kHz sine wave

Tot al E rror, Inter nal Trim

All Grades 0 mV rms–200 mV rms 0.3/0.3

200 mV to 1 V rms −1.2

T

to T

MIN

MAX

A and B Grades @ 200 mV rms
J and K Grades @ 200 mV rms 0.007

vs. Supply Voltage

@ 200 mV rms Input VS = ±5 V to ±16.5 V

V

DC Reversal Error, DC-Coupled @ 600 mV dc
Nonlinearity2, 0 mV–200 mV @ 100 mV rms

1

Using C

C

0.5/0.5
±2.0

0.7/0.7

+0.06

−0.18

+0.1 0

−0.3 0

1.3 2.5

0.25

0.35 0

= ±5 V to ±3 V

S

0
0

0

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

ERROR VS. CREST FACTOR

3

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 VS = +2.8 V, −3.2 V

V

Peak Transient Input VS = +2.8 V, −3.2 V
V
V

= ±5 V to ±16.5 V

S

±0.9

= ±5 V

S

= ±16.5 V

S

±4.0

±2.7

Input Resistance 10

12

200
1

10

Input Bias Current VS = ±3 V to ±16.5 V 1 25 1 25 pA

Low Impedance Input (Pin 1)
Signal Range

Continuous rms Level VS = +2.8 V, –3.2 V 300 300 mV rms
V

= ±5 V to ±16.5 V 1 1 V rms

S

Peak Transient Input VS = +2.8 V, −3.2 V ±1.7 ±1.7 V
V
V

= ±5 V ±3.8 ±3.8 V

S

= ±16.5 V ±11 ±11 V

S

Input Resistance 6.4 8 9.6 6.4 8 9.6 kΩ

Maximum Continuous

All supply voltages ±12 ±12 V p-p

Nondestructive Input
Input Offset Voltage

J and K Grades

A and B Grades

4

±3
±3

vs. Temperature 8 30 8 30 µV/°C

vs. Supply VS = ±5 V to ±16.5 V 50
V

= ±5 V to ±3 V 80 80 µV/V

S

150

1

Accuracy is specified with the AD736 connected as shown in Figure 18 with capacitor CC.

2

Nonlinearity is defined as the maximum deviation (in percent error) from a straight line connecting the readings at 0 mV rms and 200 mV rms. Output offset voltage is

adjusted to zero.

3

Error versus crest factor is specified as additional error for a 200 mV rms signal. Crest factor = V

4

DC offset does not limit ac resolution.

PEAK

/V rms.

2

Avg(V

)

IN

0.2/0.2

−1.2

0.007

+0.06

−0.18

1.3 2.5 % of Reading

0.25

±0.9

±4.0

V
±2.7 V
V

12

50

0.3/0.3
±2.0

0.5/0.5

+0.1

−0.3

0.35

200
1

±mV/±% of Reading
% of Reading

±mV/±% of Reading
±% of Reading/°C

%/V
%/V

% of Reading

mV rms
V rms

Ω

±3
±3

150

mV
mV

µV/V

Rev. F | Page 3 of 16

AD736

AD736J/AD736A AD736K/AD736B
Parameter Conditions Min Typ Max Min Typ Max Unit

OUTPUT CHARACTERISTICS

Output Offset Voltage

J and K Grades ±0.1
A and B Grades

±0.5
±0.5

vs.Temperature 1 20 1 20 µV/°C
vs. Supply VS = ±5 V to ±16.5 V 50

V

= ±5 V to ±3 V 50 50 µV/V

S

130

Output Voltage Swing

2 kΩ Load VS = +2.8 V, −3.2 V 0–1.6 1.7 0–1.6 1.7 V

V
V

No Load VS = ±16.5 V

= ±5 V 0–3.6 3.8 0–3.6 3.8 V

S

= ±16.5 V

S

0–4
0–4

5

12
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)

Sine wave input

for 1% Additional Error
VIN = 1 mV rms 1 1 kHz
VIN = 10 mV rms 6 6 kHz
VIN = 100 mV rms 37 37 kHz
VIN = 200 mV rms 33 33 kHz

±3 dB Bandwidth Sine wave input

VIN = 1 mV rms 5 5 kHz
VIN = 10 mV rms 55 55 kHz
VIN = 100 mV rms 170 170 kHz
VIN = 200 mV rms 190 190 kHz

Low Impedance Input (Pin 1)

Sine wave input

for 1% Additional Error
VIN = 1 mV rms 1 1 kHz
VIN = 10 mV rms 6 6 kHz
VIN = 100 mV rms 90 90 kHz
VIN = 200 mV rms 90 90 kHz

±3 dB Bandwidth Sine wave input

VIN = 1 mV rms 5 5 kHz
VIN = 10 mV rms 55 55 kHz
VIN = 100 mV rms 350 350 kHz
VIN = 200 mV rms 460 460 kHz

POWER SUPPLY

Operating Voltage Range +2.8, −3.2 ±5 ±16.5 +2.8, −3.2 ±5 ±16.5 V
Quiescent Current Zero signal 160

200

200 mV rms, No Load Sine wave input 230 270 230 270 µA

TEMPERATURE RANGE

Operating, Rated Performance

Commercial 0°C to 70°C AD736JN, AD736JR AD736KN, AD736KR
Industrial −40°C to +85°C AD736AQ, AD736AR AD736BQ, AD736BR

±0.1

50

0–4
0–4

5 V
12 V

160

±0.3
±0.3

130

200

mV
mV

µV/V

µA

Rev. F | Page 4 of 16

AD736

ABSOLUTE MAXIMUM RATINGS

Table 2.

Parameter Rating

Supply Voltage ±16.5 V
Internal Power Dissipation
Input Voltage ±V

5

200 mW

S

Output Short-Circuit Duration Indefinite
Differential Input Voltage +VS and –V

S

Storage Temperature Range (Q) –65°C to +150°C

1

C

C

V

2

IN

C

3

F

Storage Temperature Range (N, R) –65°C to +125°C
Lead Temperature Range (Soldering 60 sec) 300°C
ESD Rating 500 V

–V

4

S

Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress

Figure 2. Pin Configuration for 8-Lead PDIP (N-8), 8-Lead SOIC (RN-8),

rating only; 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.

PIN CONFIGURATION

8kΩ

FULL

WAVE

RECTIFIER

INPUT

AMPLIFIER

BIAS

SECTION

RMS CORE

and 8-Lead CERDIP (Q-8) Packages

AD736

8kΩ

OUTPUT

AMPLIFIER

8

COM

+V

7

6

OUTPUT

C

5

S

AV

00834-F-001

5

8-Lead PDIP Package: θJA = 165°C/W

8-Lead CERDIP Package: θ
8-Lead SOIC Package: θ

= 110°C/W

JA

= 155°C/W

JA

ESD CAUTION

ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on
the human body and test equipment and can discharge without detection. Although this product features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance
degradation or loss of functionality.

Rev. F | Page 5 of 16