Datasheet AD737 Datasheet (ANALOG DEVICES)

Low Cost, Low Power,

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FEATURES

Computes

True rms value Average rectified value Absolute value

Provides

200 mV full-scale input range (larger inputs with

input a

ttenuator) Direct interfacing with 3½ digit CMOS ADCs High input impedance: 10 Low input bias current: 25 pA maximum High accuracy: ±0.2 mV ± 0.3% of reading RMS conversion with signal crest factors up to 5 Wide power supply range: ±2.5 V to ±16.5 V Low power: 160 μA maximum supply current No external trims needed for specified accuracy

A general-purpose, buffered voltage output version also

a

vailable (AD736)

GENERAL DESCRIPTION

The AD7371 is a low power, precision, monolithic true rms-to-dc converter. It is laser trimmed to provide a maximum error of ±0.2 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 nonrms precision rectifiers in many applications. Compared to these circuits, the AD737 offers higher accuracy at equal or lower cost.

The AD737 can compute the rms value of both ac and dc input v

oltages. It can also be operated ac-coupled by adding one external capacitor. In this mode, the AD737 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 AD737 has no output buffer amplifier, thereby significantly r

educing dc offset errors occurring at the output, which makes

the device highly compatible with high input impedance ADCs.

Requiring only 160 µA of power supply current, the AD737 is

ptimized for use in portable multimeters and other battery-

o powered applications. This converter also provides a power-down feature that reduces the power-supply standby current to less than 30 µA.

1

Protected under U.S. Patent Number 5,495,245.

12

Ω

True RMS-to-DC Converter

AD737

FUNCTIONAL BLOCK DIAGRAM

8kΩ

1

C

V

2

POWER

DOWN

–V

IN

3

4

S

INPUT

AMPLIFI ER

BIAS

SECTION

Figure 1.

Two signal input terminals are provided in the AD737. A high

12

im

pedance (10

Ω) FET input interfaces directly with high R input attenuators, and a low impedance (8 kΩ) input accepts rms voltages to 0.9 V while operating from the minimum power supply voltage of ±2.5 V. The two inputs can be used either single ended or differentially.

The AD737 achieves 1% of reading error bandwidth, exceeding

z for input amplitudes from 20 mV rms to 200 mV rms,

10 kH while consuming only 0.72 mW.

The AD737 is available in four performance grades. The AD737J an

d AD737K grades are rated over the commercial temperature range of 0°C to 70°C. The AD737JR-5 is tested with supply voltages of ±2.5 V dc. The AD737A and AD737B grades are rated over the industrial temperature range of

−40°C to +85°C. The AD737 is available in three low cost, 8lead packages: PDIP, SOIC_N, and CERDIP.

PRODUCT HIGHLIGHTS

1. Capable of computing the average rectified value, absolute

value, or true rms value of various input signals.

2. Onl

3. The lo

y one external component, an averaging capacitor, is

required for the AD737 to perform true rms measurement.

w power consumption of 0.72 mW makes the

AD737 suitable for battery-powered applications.

AD737

FULL-WAVE

RECTIFI ER

RMS CORE

8kΩ

8

COM

+V

7

6

OUTPUT

C

5

S

AV

00828-001

Rev. G

Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Anal og Devices for its use, nor for any infringements of patents or ot her 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.

AD737

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REVISION HISTORY

12/06—Rev. F to Rev. G

Changes to Specifications................................................................ 3

Reorganized Typical Performance Characteristics ...................... 8

Changes to Figure 21...................................................................... 11

Reorganized Theory of Operation Section ................................. 12

Reorganized Applications Section................................................ 14

Added Scaling Input and Output Voltages Section.................... 14

Deleted Application Circuits Heading......................................... 16

Changes to Figure 28...................................................................... 16

Added AD737 Evaluation Board Section .................................... 18

Updated Outline Dimensions....................................................... 20

Changes to Ordering Guide.......................................................... 21

1/05—Rev. E to Rev. F

Updated Format ..................................................................Universal

Added Functional Block Diagram.................................................. 1

Changes to General Description Section ...................................... 1

Changes to Pin Configurations and Function D

escriptions Section ........................................................................ 6

Changes to Typical Performance Characteristics Section........... 7

Changes to Table 4.......................................................................... 11

Change to Figure 24 ....................................................................... 12

Change to Figure 27 ....................................................................... 15

Changes to Ordering Guide.......................................................... 18

6/03—Rev. D to Rev. E

Added AD737JR-5..............................................................Universal

Changes to Features ..........................................................................1

Changes to General Description .....................................................1

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

Changes to Absolute Maximum Ratings........................................4

Changes to Ordering Guide.............................................................4

Added TPCs 16 through 19 .............................................................6

Changes to Figures 1 and 2 ..............................................................8

Changes to Figure 8........................................................................ 11

Updated Outline Dimensions....................................................... 12

12/02—Rev. C to Rev. D

Changes to Functional Block Diagram...........................................1

Changes to Pin Configuration.........................................................4

Figure 1 Replaced ..............................................................................8

Changes to Figure 2...........................................................................8

Figure 5 Replaced ........................................................................... 10

Changes to Application Circuits Figures 4, 6–8 ......................... 10

Outline Dimensions Updated....................................................... 12

12/99—Rev. B to Rev. C

Rev. G | Page 2 of 24

AD737

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SPECIFICATIONS

TA = 25°C, ±VS = ±5 V except as noted, CAV = 33 µF, CC = 10 µF, f = 1 kHz, sine wave input applied to Pin 2, unless otherwise specified. Specifications shown in boldface are tested on all production units at final electrical test. Results from these tests are used to calculate outgoing quality levels.

Table 1.

AD737A, AD737J AD737B, AD737K AD737J-5 Parameter Conditions Min Typ Max Min Typ Max Min Typ Max Unit

ACCURACY

Total Error EIN = 0 to 200 mV rms 0.2/0.3

±VS = ±2.5 V 0.2/0.3 ±VS = ±2.5 V,

E

Over Temperature

AQ and BQ EIN = 200 mV rms JN, JR, KN, KR EIN = 200 mV rms,

AN and AR EIN = 200 mV rms,

Vs. Supply Voltage

E

DC Reversal Error DC coup led,

V

Nonlinearity

Input to Pin 1

Total Error, External Trim

ADDITIONAL CREST FACTOR

4

ERROR

For Crest Factors from 1 to 3

C

For Crest Factors from 3 to 5

INPUT CHARACTERISTICS

High-Z Input (Pin 2) Signal Range

Continuous RMS Level

±VS = +2.8 V/−3.2 V ±VS = ±5 V to ±16.5 V

input to Pin 1

= 200 mV to 1 V rms −1.2

IN

= ±2.5 V

±V

S

= ±2.5 V

±V

S

= 200 mV rms,

IN

= ±2.5 V to ±5 V

±V

S

= 200 mV rms,

IN

= ±5 V to ±16.5 V

±V

S

= 600 mV dc

V

IN

= 200 mV dc,

IN

= ±2.5 V

±V

2

3

S

EIN = 0 to 200 mV rms, @ 100 mV rms

AC coupled,

= 100 mV rms, after

E

IN

correction, ±V EIN = 0 to 200 mV rms 0.1/0.2 0.1/0.2 0.1/0.2 ±mV/±POR

CAV = CF = 100 μF 0.7 0.7 %

= 22 μF, CF = 100 μF,

AV

±V

= ±2.5 V,

S

input to Pin 1 CAV = CF = 100 μF 2.5 2.5 %

±VS = +2.5 V

= ±2.5 V

S

0.2/0.3

0.007 0.007 0.02 ±POR/°C

0.014 0.014 ±POR/°C

0

1.3 2.5 1.3 2.5 POR

1.7 2.5 POR

0

0.02 0.1 POR

1.7 %

−0.18

0.06

0.25

0.4/0.5

±2.0

0.5/0.7

−0.3 0

0.1 0

0.35 0

200 1

0.2/0.2

−1.2

−0.18

0.06

0.25

0.2/0.3

±2.0

0.3/0.5

−0.3 0

0.1 0

0.35

200 1

±mV/±POR

0.4/0.5

POR

±POR/°C

−0.18

0.06

POR

mV rms V rms

−0.3

0.1

200

POR POR

%/V

mV rms

1

Rev. G | Page 3 of 24

AD737

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AD737A, AD737J AD737B, AD737K AD737J-5 Parameter Conditions Min Typ Max Min Typ Max Min Typ Max Unit

Peak Transient Input

±VS = +2.8 V/−3.2 V ±VS = ±5 V ±2.7 ±2.7 V ±VS = ±16.5 V Input Resistance 1012 1012 1012 Ω Input Bias

Current

Low-Z Input (Pin 1) Signal Range

Continuous RMS Level

±VS = +2.8 V/−3.2 V 300 300 mV rms ±VS = ±5 V to ±16.5 V 1 1 V rms

Peak Transient Input

±VS = +2.8 V/−3.2 V ±1.7 ±1.7 V ±VS = ±5 V ±3.8 ±3.8 V ±VS = ±16.5 V ±11 ±11 V

Input Resistance 6.4 8 9.6 6.4 8 9.6 6.4 8 9.6 kΩ

Maximum Continuous Nondestructive Input

Input Offset

5

Voltage Over the Rated

Operating Temperature Range

Vs. Supply VS = ±2.5 V to ±5 V 80 80 80 μV/V

V

OUTPUT CHARACTERISTICS

Output Voltage Swing

±VS = ±5 V −3.3 −3.4 −3.3 −3.4 V ±VS = ±16.5 V ±VS = ±2.5 V, input

Output Resistance

FREQUENCY RESPONSE

High-Z Input (Pin 2)

1% Additional Error

V V V

= +2.5 V

±V

S

input to Pin 1

±VS = ±5 V 1 25 1 25 1 25 pA

±VS = +2.5 V 300 mV rms

±VS = +2.5 V ±1.7 V

All supply voltages ±12 ±12 ±12 V p-p

AC coupled

8 30 8 30 8 30 μV/°C

= ±5 V to ±16.5 V 50 150 50 150 μV/V

S

No load

±VS = +2.8 V/−3.2 V −1.6 −1.7 −1.6 −1.7 V

to Pin 1 DC 6.4 8 9.6 6.4 8 9.6 6.4 8 9.6 kΩ

VIN = 1 mV rms 1 1 1 kHz

= 10 mV rms 6 6 6 kHz

IN

= 100 mV rms 37 37 37 kHz

IN

= 200 mV rms 33 33 33 kHz

IN

±0.9

±4.0

−4 −5

−1.1 –0.9 V

±3

−4 −5

±0.9

±4.0

V

±3

V

±0.6

±3

mV

Rev. G | Page 4 of 24

AD737

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AD737A, AD737J AD737B, AD737K AD737J-5 Parameter Conditions Min Typ Max Min Typ Max Min Typ Max Unit

3 dB Bandwidth

V V V

Low-Z Input (Pin 1)

1% Additional Error

V V V V 3 dB

Bandwidth V V V

POWER-DOWN MODE

Disable Voltage 0 0 V Input Current,

PD Enabled

POWER SUPPLY

Operating Voltage Range

Current No input 120

Rated input 170 210 170 210 170 210 μA Powered down 25 40 25 40 25 40 μA

1

POR = % of reading.

2

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

3

After fourth-order error correction using the equation

y = − 0.31009x4 − 0.21692x3 − 0.06939x2 + 0.99756x + 11.1 × 10−6

where y is the corrected result and x is the device output between 0.01 V and 0.3 V.

4

Crest factor error is specified as the additional error resulting from the specific crest factor, using a 200 mV rms signal as a reference. The crest factor is defined as

V

/V rms.

PEAK

5

DC offset does not limit ac resolution.

VIN = 1 mV rms 5 5 5 kHz

= 10 mV rms 55 55 55 kHz

IN

= 100 mV rms 170 170 170 kHz

IN

= 200 mV rms 190 190 190 kHz

IN

VIN = 1 mV rms 1 1 1 kHz

= 10 mV rms 6 6 6 kHz

IN

= 40 mV rms 25 kHz

IN

= 100 mV rms 90 90 90 kHz

IN

= 200 mV rms 90 90 90 kHz

IN

VIN = 1 mV rms 5 5 5 kHz

= 10 mV rms 55 55 55 kHz

IN

= 100 mV rms 350 350 350 kHz

IN

= 200 mV rms 460 460 460 kHz

IN

VPD = VS 11 11 μA

+2.8/−3.2 ±5 ±16.5 +2.8/−3.2 ±5 ±16.5 ±2.5 ±5 ±16.5 V

160

120

160

120

160

μA

Rev. G | Page 5 of 24

AD737

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ABSOLUTE MAXIMUM RATINGS

Table 2.

Parameter Rating

Supply Voltage ±16.5 V Internal Power Dissipation 200 mW Input Voltage ±VS Output Short-Circuit Duration Indefinite Differential Input Voltage +VS and −VS Storage Temperature Range

CERDIP (Q-8) −65°C to +150°C

PDIP (N-8) and SOIC_N (R-8) −65°C to +125°C Lead Temperature Range, Soldering (60 sec) 300°C ESD Rating 500 V

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

THERMAL RESISTANCE

θJA is specified for the worst-case conditions, that is, a device soldered in a circuit board for surface-mount packages.

Table 3. Thermal Resistance

Package Type θJA Unit

8-Lead CERDIP (Q-8) 110 °C/W 8-Lead PDIP (N-8) 165 °C/W 8-Lead SOIC_N (R-8) 155 °C/W

ESD CAUTION

Rev. G | Page 6 of 24

AD737

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PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS

C

V

POWER DOW N

–V

C

IN

S

1

AD737

2

3

TOP VIEW

(Not to Scale)

4

8

7

6

5

COM

+V

S

OUTPUT

C

AV

1

C

AD737

2

V

IN

TOP VIEW

–V

3

4

S

(Not to Scale)

POWER DOW N

00828-002

8

COM

+V

7

6

OUTPUT

5

C

1

C

S

AV

00828-003

POWER DOW N

V

–V

C

IN

S

2

AD737

TOP VIEW

3

(Not to Scale)

4

Figure 2. SOIC_N Pin Configuration (R-8) Figure 3. CERDIP Pin Configuration (Q-8) Figure 4. PDIP Pin Configuration (N-8)

Table 4. Pin Function Descriptions

Pin No. Mnemonic Description

1 CC Coupling Capacitor for Indirect DC Coupling. 2 VIN RMS Input. 3 POWER DOWN 4 –V 5 C

Negative Power Supply.

S

Averaging Capacitor.

AV

6 OUTPUT 7 +V

Positive Power Supply.

S

Disables the AD737. Low is enabled; high is powered down.

Output.

8 COM Common.

8

COM

7

+V

6

OUTPUT

5

C

S

AV

00828-004

Rev. G | Page 7 of 24

AD737

V

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TYPICAL PERFORMANCE CHARACTERISTICS

TA = 25°C, ±VS = ±5 V (except AD737J-5, ±VS = ±2.5 V), CAV = 33 µF, CC = 10 µF, f = 1 kHz, sine wave input applied to Pin 2, unless otherwise specified.

0.7

0.5

VIN = 200mV rms C

= 100µF

AV

C

= 22µF

F

10

CAV = 22µF, CF = 4.7µF, CC = 22µF

1V

0.3

0.1

0

–0.1

–0.3

ADDITIONA L ERROR (% of Read ing)

–0.5

04286121410 16

SUPPLY VOLTAGE (±V)

Figure 5. Additional Error vs. Supply Voltage

16

DC COUPL ED

14

12

10

8

6

4

PEAK INPUT BEFO RE CLIPPI NG (V)

2

0

04286121410 16

PIN 1

PIN 2

SUPPLY VOLTAGE (±V)

Figure 6. Maximum Input Level vs. Supply Voltage

25

20

100mV

10mV

INPUT LEVEL (rms)

1mV

00828-005

100µV

0.1 1 10010 1000

1% ERROR

10% ERROR

FREQUENCY (kHz)

–3dB

00828-008

Figure 8. Frequency Response Driving Pin 1

10

CAV = 22µF, CF = 4.7µF, CC = 22µF

1V

100mV

10mV

INPUT LEVEL (rms)

1mV

00828-006

100µV

0.1 1 10010 1000

1% ERROR

FREQUENCY (kHz )

10% ERROR

–3dB

00828-009

Figure 9. Frequency Response Driving Pin 2

6

3ms BURST OF 1kHz = 3 CYCLES 200mV rms SIGNA L

5

= 22µF

C

= 100µF

C

F

4

CAV = 10µF

CAV = 33µF

15

SUPPLY CURRENT (µA)

10

5

0246 81012141618

DUAL SUPPLY VOLTAGE (±V)

Figure 7. Supply Current (Power-Down Mode) vs. Supply Voltage (Dual)

00828-007

3

2

1

ADDITIONAL ERRO R (% of Readi ng)

0

12345

CREST FACTOR (V

Figure 10. Additional Error vs. Crest Factor

Rev. G | Page 8 of 24

CAV = 250µF

/V rms)

PEAK

CAV = 100µF

00828-010

AD737

V

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0.8 VIN = 200mV rms

C

= 100µF

AV

0.6 C

= 22µF

F

0.4

0.2

0

–0.2

–0.4

ADDITIONA L ERROR (% of Read ing)

–0.6

–0.8

–60 –20–40 200 60 80 100 12040 140

TEMPERATURE (°C)

Figure 11. Additional Error vs. Temperature

00828-011

1.0

0.5

0

–0.5

–1.0

ERROR (% of Read ing)

–1.5

–2.0

CAV = 22µF, CC = 47µF,

C

= 4.7µF

F

–2.5

10mV 100mV 1V 2V

INPUT LEVEL (rms)

Figure 14. Error vs. RMS Input Level Using Circuit of Figure 29

00828-014

500

400

300

200

DC SUPPLY CURRENT (µA)

100

0

0 0.2 0.4 0.6 0.8 1.0

RMS INPUT LEVEL (V)

Figure 12. DC Supply Current vs. RMS Input Level

10m

AC COUPL ED

1mV

100

10

AVERAGING CAPACITOR (µF)

00828-012

1

10 100 1k

–1%

FREQUENCY (Hz)

–0.5%

VIN = 200mV rms C

= 47µF

C

= 47µF

F

00828-015

Figure 15. Value of Averaging Capacitor vs. Frequency

for Specif

ied Averaging Error

1

–1%

100mV

–0.5%

INPUT LEVEL (rms)

100µV

10µV

100 1k 10k 100k

–3dB FREQUENC Y (Hz)

Figure 13. RMS Input Level vs. –3 dB Frequency

00828-013

10mV

INPUT LEVEL (rms)

1mV

1 10 100 1k

Figure 16. RMS Input Level vs. Frequency for Specified Averaging Error

Rev. G | Page 9 of 24

FREQUENCY ( Hz)

AC COUPLED C

= 10µF, CC = 47µF,

AV

C

= 47µF

F

00828-016

AD737

V

n

A

V

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4.0

10

3.5

3.0

2.5

2.0

INPUT BIAS CURRENT (pA)

1.5

1.0 024 68 121410 16

SUPPLY VOLTAGE (±V)

Figure 17. Input Bias Current vs. Supply Voltage

1

100mV

CAV = 10µF

10mV

INPUT LEVEL (rms)

1mV

CAV = 33µF

CC = 22µF C

= 0µF

F

CAV = 100µF

1nA

100pA

10pA

INPUT BIAS CURRENT

1pA

00828-017

100fA

–55 –35 –15 5 25 65 85 10545 125

TEMPERATURE (°C)

00828-019

Figure 19. Input Bias Current vs. Temperature

10

VS=±2.5V, C

= 22µF, CF = 4.7µF, CC = 22µF

AV

1V

100mV

10mV

INPUT LEVEL (rms)

1mV

100µV

1ms 10ms 100ms 1s 10s 100s

SETTLING TIME

Figure 18. RMS Input Level vs. Settling Time for Three Values of C

00828-018

AV

100µV

0.1 1 10 100 1000

FREQUENCY ( kHz)

Figure 20. Frequency Response Driving Pin 1

00828-020

Rev. G | Page 10 of 24

AD737

V

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10

100mV

VS=±2.5V, C

= 22µF, CF = 4.7µF, CC = 22µF

AV

1V

1.0

0.5

0

–0.5

10mV

INPUT LEVEL (rms)

1mV

100µV

0.1 1 10 100 1000

0.5%

10%

–3dB

1%

FREQUENCY (kHz)

Figure 21. Error Contours Driving Pin 1

5

3 CYCLES OF 1kHz 200mV rms V

= ±2.5V

S

4

C

= 22µF

C

= 100µF

F

3

2

1

ADDITIONA L ERROR (% of Read ing)

0

1234

CREST FACTOR

CAV = 22µF

CAV = 10µF

CAV = 100µF

Figure 22. Additional Error vs. Crest Factor for Various Values of C

CAV = 33µF

CAV = 220µF

00828-021

00828-022

5

AV

–1.0

ERROR (% of Read ing)

–1.5

–2.0

CAV = 22µF, VS = ±2.5V C

= 47µF, CF = 4.7µF

C

–2.5

10mV 100mV 1V 2V

INPUT LEVEL (rms)

00828-023

Figure 23. Error vs. RMS Input Level Driving Pin 1

Rev. G | Page 11 of 24

AD737

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THEORY OF OPERATION

As shown in Figure 24, the AD737 has four functional subsections: an input amplifier, a full-wave rectifier, an rms core, and a bias section. The FET input amplifier allows a high impedance, buffered input at Pin 2 or a low impedance, wide dynamic range input at Pin 1. The high impedance input, with its low input bias current, is ideal for use with high impedance input attenuators. The input signal can be either dc coupled or ac coupled to the input amplifier. Unlike other rms converters, the AD737 permits both direct and indirect ac coupling of the inputs. AC coupling is provided by placing a series capacitor between the input signal and Pin 2 (or Pin 1) for direct coupling and between Pin 1 and ground (while driving Pin 2) for indirect coupling.

AC

C

10µF

C =

+

DC

OPTIONAL RETURN PAT H

CURRENT MODE ABSOLUTE VAL UE

C

V

IN

POWER

DOWN

–V

1

C

IN

2

3

S

4

8kΩ

FET

OP AMP

1

<10pA

B

BIAS

SECTION

RMS

TRANSLINEAR

CORE

POSITIVE SUPPLY

COMMON

NEGATI VE SUPPLY

C

33µF

8kΩ

A

+

0.1µF

8

COM

C

F

+

10µF (OPTIONAL

+V

7

S

LPF)

6

OUTPUT

C

5

AV

+V

S

–V

S

Figure 24. AD737 True RMS Circuit (Test Circuit)

The output of the input amplifier drives a full-wave precision rectifier, which, in turn, drives the rms core. It is the core that provides the essential rms operations of squaring, averaging, and square rooting, using an external averaging capacitor, C

Without C

, the rectified input signal passes through the core

AV

.

AV

unprocessed, as is done with the average responding connection (see Figure 26). In the average responding mode, averaging is ca

rried out by an RC post filter consisting of an 8 kΩ internal

scale factor resistor connected between Pin 6 and Pin 8 and an

external averaging capacitor, C tional filtering stage reduces any output ripple that was not removed by the averaging capacitor.

Finally, the bias subsection permits a power-down function.

educes the idle current of the AD737 from 160 µA to a

This r mere 30 µA. This feature is selected by connecting Pin 3 to Pin 7 (+V

).

S

TYPES OF AC MEASUREMENT

The AD737 is capable of measuring ac signals by operating as either an average responding converter or a true rms-to-dc converter. As its name implies, an average responding converter computes the average absolute value of an ac (or ac and dc) voltage or current by full-wave rectifying and low-pass filtering the input signal; this approximates the average. The resulting output, a dc average level, is then scaled by adding (or reducing) gain; this scale factor converts the dc average reading to an rms equivalent value for the waveform being measured. For example, the average absolute value of a sine wave voltage is 0.636 that of V

; the corresponding rms value is 0.707 times V

PEAK

Therefore, for sine wave voltages, the required scale factor is

1.11 (0.707 divided by 0.636).

In contrast to measuring the average value, true rms measure-

ent is a universal language among waveforms, allowing the

m magnitudes of all types of voltage (or current) waveforms to be compared to one another and to dc. RMS is a direct measure of the power or heating value of an ac voltage compared to that of a dc voltage; an ac signal of 1 V rms produces the same amount of heat in a resistor as a 1 V dc signal.

Mathematically, the rms value of a voltage is defined (using a

plified equation) as

sim

2

)( rms V

VAvg=

This involves squaring the signal, taking the average, and then

taining the square root. True rms converters are smart recti-

ob fiers; they provide an accurate rms reading regardless of the type of waveform being measured. However, average responding

00828-024

converters can exhibit very high errors when their input signals deviate from their precalibrated waveform; the magnitude of the error depends on the type of waveform being measured. As an example, if an average responding converter is calibrated to measure the rms value of sine wave voltages and then is used to measure either symmetrical square waves or dc voltages, the converter has a computational error 11% (of reading) higher than the true rms value (see

The transfer function for the AD737 is

2

VAvg=

OUT

IN

. In the rms circuit, this addi-

F

Table 5 ).

)( V

PEAK

.

Rev. G | Page 12 of 24

AD737

www.BDTIC.com/ADI

DC ERROR, OUTPUT RIPPLE, AND AVERAGING ERROR

Figure 25 shows the typical output waveform of the AD737 with a sine wave input voltage applied. As with all real-world devices, the ideal output of V the output contains both a dc and an ac error component.

E

O

Figure 25. Output Waveform for Sine Wave Input Voltage

As shown, the dc error is the difference between the average of the output signal (when all the ripple in the output has been removed by external filtering) and the ideal dc output. The dc error component is, therefore, set solely by the value of the averaging capacitor used—no amount of post filtering (using a very large postfiltering capacitor, C to equal its ideal value. The ac error component, an output ripple, can be easily removed using a large enough C

In most cases, the combined magnitudes of the dc and ac error

mponents must be considered when selecting appropriate

co values for C

and CF capacitors. This combined error, repre-

AV

senting the maximum uncertainty of the measurement, is termed the averaging error and is equal to the peak value of the output ripple plus the dc error. As the input frequency increases, both error components decrease rapidly. If the input frequency doubles, the dc error and ripple reduce to one-quarter and one-half of their original values, respectively, and rapidly become insignificant.

= VIN is never exactly achieved; instead,

OUT

IDEAL

E

O

DC ERROR = EO – EO (IDEAL)

DOUBLE-FREQUENCY

RIPPLE

AVERAGE E

) allows the output voltage

F

= E

O

TIME

.

F

00828-026

AC MEASUREMENT ACCURACY AND CREST FACTOR

The crest factor of the input waveform is often overlooked when determining the accuracy of an ac measurement. Crest factor is defined as the ratio of the peak signal amplitude to the rms amplitude (crest factor = V

/V rms). Many common

PEAK

waveforms, such as sine and triangle waves, have relatively low crest factors (≥2). Other waveforms, such as low duty cycle pulse trains and SCR waveforms, have high crest factors. These types of waveforms require a long averaging time constant to average out the long time periods between pulses.

hows the additional error vs. the crest factor of the AD737 for

s various values of C

.

AV

Figure 10

CALCULATING SETTLING TIME

Figure 18 can be used to closely approximate the time required for the AD737 to settle when its input level is reduced in amplitude. The net time required for the rms converter to settle is 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 (reduced) input level of 1 mV. From th

e 100 mV line intersects the 33 µF line) is approximately 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 is 8 seconds minus 80 ms, which is 7.92 seconds.

Note, because of the smooth decay characteristic inherent with a ca

pacitor/diode combination, this is the total settling time to the final value (not the settling time to 1%, 0.1%, and so on, of the final value). Also, this graph provides the worst-case settling time, because the AD737 settles very quickly with increasing input levels.

Figure 18, the initial settling time (where

Table 5. Error Introduced by an Average Respondi

Type of Waveform 1 V Peak Amplitude

Undistorted Sine Wave 1.414 0.707 0.707 0 Symmetrical Square Wave 1.00 1.00 1.11 11.0 Undistorted Triangle Wave 1.73 0.577 0.555 −3.8 Gaussian Noise (98% of

Peaks <1 V) Rectangular 2 0.5 0.278 −44 Pulse Train 10 0.1 0.011 −89 SCR Waveforms

50% Duty Cycle 2 0.495 0.354 −28 25% Duty Cycle 4.7 0.212 0.150 −30

Crest Factor

/V rms)

(V

PEAK

3 0.333 0.295 −11.4

ng Circuit When Measuring Common Waveforms

True RM S Va

lue (V)

Reading of an Average Responding Circuit Calibrated to an RMS Sine Wave Value (V) Error (%)

Rev. G | Page 13 of 24

AD737

R

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APPLICATIONS

RMS MEASUREMENT—CHOOSING OPTIMUM VALUE FOR C

Because the external averaging capacitor, CAV, holds the rectified input signal during rms computation, its value directly affects the accuracy of the rms measurement, especially at low frequencies. Furthermore, because the averaging capacitor appears across a diode in the rms core, the averaging time constant increases exponentially as the input signal is reduced. This means that as the input level decreases, errors due to nonideal averaging decrease, while the time it takes for the circuit to settle to the new rms level increases. Therefore, lower input levels allow the circuit to perform better (due to increased averaging) but increase the waiting time between measurements. When selecting C settling time is required.

AV

, a trade-off between computational accuracy and

RAPID SETTLING TIMES VIA THE AVERAGE RESPONDING CONNECTION

Because the average responding connection shown in Figure 26 does not use an averaging capacitor, its settling time does not vary with input signal level; it is determined solely by the RC time constant of C

C

V

IN

POWE

DOWN

and the internal 8 kΩ output scaling resistor.

F

8kΩ

1

C

2

3

–V

4

S

INPUT

AMPLIFI ER

BIAS

SECTION

POSITIVE SUPPLY

COMMON

NEGATIVE SUPPLY

Figure 26. AD737 Average Responding Circuit

AD737

FULL-WAVE

RECTIFI ER

RMS

CORE

8kΩ

0.1µF

8

COM

+V

7

S

6

OUTPUT

C

5

AV

+V

S

–V

S

+

C

F

33µF

V

OUT

00828-025

SELECTING PRACTICAL VALUES FOR CAPACITORS

Tabl e 6 provides practical values of CAV and CF for several common applications.

The input coupling capacitor, C internal input scaling resistor, determines the −3 dB low frequency roll-off. This frequency, F

F

L

1

××π=80002

, in conjunction with the 8 kΩ

C

, is equal to

L

(

FaradsinC

C

(1)

)

Note that at F (−3 dB) of reading. To reduce this error to 0.5% of reading, choose a value of C frequency to be measured.

In addition, if the input voltage has more than 100 mV of dc o

ffset, the ac coupling network at Pin 2 is required in addition

to Capacitor C

SCALING INPUT AND OUTPUT VOLTAGES

The AD737 is an extremely flexible device. With minimal external circuitry, it can be powered with single- or dualpolarity power supplies, and input and output voltages are independently scaleable to accommodate nonmatching I/O devices. This section describes a few such applications.

Extending or Scaling the Input Range

For low supply voltage applications, the maximum peak voltage to the device is extended by simply applying the input voltage to Pin 1 across the internal 8 kΩ input resistor. The AD737 input circuit functions quasi differentially, with a high impedance, FET input at Pin 2 (noninverting) and a low impedance input at Pin 1 (inverting, see

s a voltage-to-current converter connected to the summing

a node of a feedback loop around the input amplifier. Because the feedback loop servos the summing node voltage to match the voltage at Pin 2, the maximum peak input voltage increases until the internal circuit runs out of headroom, approximately double for a symmetrical dual supply.

Battery Operation

All the level-shifting for battery operation is provided by the 3½ digit converter, shown in Figure 27. Alternatively, an

ernal op amp adds flexibility by accommodating nonzero

ext common-mode voltages and providing output scaling and offset to zero. When an external operational amplifier is used, the output polarity is positive going.

Figure 28 shows an op amp used in a single-supply application.

ote the combined input resistor value (R1 + R2 + 8 kΩ)

N matches that of the Feedback Resistor R5. In this instance, the magnitudes of the output dc voltage and the rms of the ac input are equal. R3 and R4 provide current to offset the output to 0 V.

Scaling the Output Voltage

The output voltage may be scaled to the input rms voltage. For e

xample, assume the AD737 is retrofitted to an existing application using an averaging responding circuit (full-wave rectifier). The power supply is 12 V; the input voltage is 10 V ac, and the desired output is 6 V dc.

, the amplitude error is approximately −30%

L

that sets FL at one-tenth of the lowest

C

.

C

Figure 26). The internal 8 kΩ resistor behaves

Rev. G | Page 14 of 24

AD737

www.BDTIC.com/ADI

For convenience, use the same combined input resistance as shown in Figure 28. Calculate the rms input current as

= A 125

INMAG

Next, using the I feedback resistor required for 6 V output using

R

FB

Select the closest-value standard 1% resistor, 47.5 kΩ.

Since the supply is 12 V, the common-mode voltage at the divider R7/R8 is (R3 + R4) is equal to the feedback resistor, or 47.5 kΩ.

Table 6. AD737 Capacitor Selection

Application RMS Input Level

General-Purpose RMS Computation

200 Hz 5 15 1 36 ms 0 mV to 200 mV 20 Hz 5 33 10 360 ms 200 Hz 5 3.3 1 36 ms General-Purpose Average

Responding 200 Hz None 3.3 120 ms 0 mV to 200 mV 20 Hz None 33 1.2 s 200 Hz None 3.3 120 ms SCR Waveform

Measurement 60 Hz 5 82 27 1.0 s 0 mV to 100 mV 50 Hz 5 50 33 1.2 s 60 Hz 5 47 27 1.0 s Audio Applications

Speech 0 mV to 200 mV 300 Hz 3 1.5 0.5 18 ms Music 0 mV to 100 mV 20 Hz 10 100 68 2.4 s

1

Settling time is specified over the stated rms input level with the input signal increasing from zero. Settling times are greater for decreasing amplitude input signals.

OUTMAG

V 6

=

A 125

μ

6 V, and the combined resistor value

V 10

++

k 8 k 2.5 k 69.8

value from Equation 2, calculate the

k 48.1

=

(3)

0 V to 1 V 20 Hz 5 150 10 360 ms

0 V to 1 V 20 Hz None 33 1.2 s

0 mV to 200 mV 50 Hz 5 100 33 1.2 s

II =μ=

(2)

OUTMAG

Low Frequency C

utoff (−3 dB)

R2 is used to calibrate the transfer function (gain), and R4 sets t

he output voltage to zero with no input voltage.

Perform calibration as follows:

ith no ac input applied, adjust R4 for 0 V.

1. W

2. A

pply a known input to the input.

3. A

djust trimmer R2 until the input and output match.

The op amp selected for any single-supply application must be a ra

il-to-rail type, for example an AD8541, shown in Figure 28.

F

or higher voltages, a higher voltage part, such as an OP196, can be used. When calibrating to 0 V, the specified voltage above ground for the operational amplifier must be taken into account. Adjust R4 slightly higher as appropriate.

Maximum Crest Factor C

(μF) CF (μF) Settling Time1 to 1%

AV

Rev. G | Page 15 of 24

AD737

V

T

R

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IN

SWITCH CLO SED

ACTIVATES

POWER-DOWN

MODE. AD737 DR AW S

JUST 40µA IN THIS MODE

1PRV

0.01µF

9MΩ

900kΩ

90kΩ

10kΩ

200mV

2V

20V

200V

1µF

1N4148

47kΩ

1W

1N4148

+

POWER

DOWN

–V

C

10µF

C

V

IN

+

C

+

C

8kΩ

1

2

3

S

4

INPUT

AMPLIFIER

BIAS

SECTION

1µF

AD737

FULL-WAVE

RECTIFIER

RMS

CORE

8kΩ

AD589

COM

8

+V

S

7

OUTPUT

6

C

AV

5

+

1.23V

+V

33µF

20kΩ

200kΩ

50kΩ

1MΩ

0.1µF

+V

S

1

/2 DIGIT ICL7136

3 TYPE CONVERT ER

REF HIGH

REF LOW

COMMON

LOW

ANALOG

HIGH

–V

S

+

9V

00828-027

Figure 27. 3½ Digit DVM Circuit

INPUT SCALE FACTOR ADJ

R1

69.8kΩ

1%

R2

5kΩ

0.01µF

C

F

C

1

C

V

2

3

4

IN

POWER DOWN

–V

S

AD737

C2

COM

+V

OUTPUT

C

8

NC

5V

7

S

OUTPUT ZERO

6

5

AV

R3

78.7kΩ

ADJUST

R4

5kΩ

C3

0.01µF

0.47µF

80.6kΩ

1

2

AD8541AR

3

4

R5

5V

0.01µF

7

6

5

OUTPUT

INPU

C1

0.47µF

NC = NO CONNECT

C

AV

33µF

+

C4

2.2µF

C5

1µF

R7

100kΩ

2.5V

R8

+

Figure 28. Battery-Powered Operation for 200 mV Maximum RMS Full-Scale Input

C

V

IN

POWE

DOWN

10µF

+

8kΩ

1

C

FULL-WAVE

2

AMPLIFIER

BIAS

3

SECTION

–V

S

4

INPUT

RECTIFIER

RMS

CORE

C

AV

33µF

+

100Ω

AD737

8kΩ

SCALE FACTOR

ADJUST

COM

8

200Ω

+V

7

S

10µF

OUTPUT

6

C

AV

5

+

C

F

V

OUT

00828-029

Figure 29. External Scale Factor Trim

5V

00828-028

Rev. G | Page 16 of 24

AD737

T

A

www.BDTIC.com/ADI

C

10µF

C

8kΩ

+

1

2

V

IN

POWER

3

DOWN

–V

S

4

NC = NO CONNECT *Q1, Q2 PART OF RCA CA3046 OR SI MILAR NPN T RANSISTO R ARRAY.

**R1 + R

IN Ω = 10,000 ×

CAL

AMPLIFIER

BIAS

SECTION

R

CAL

INPUT

**

0dB INPUT LEVEL IN V

AD737

FULL-WAVE

RECTIFIE R

RMS

CORE

+

C

AV

R1**

4.3V

COM

8kΩ

8

NC

+V

7

S

OUTPUT

6

C

AV

5

I

REF

Figure 30. dB Output Connection

OFFSET

DJUST

+V

S

500kΩ

1MΩ

1kΩ

–V

S

14

13

Q1

12

*

2

3

10

3500PPM/°C

60.4Ω

SCALE

FAC TOR

TRIM

AD711

*

11

Q2

9

1kΩ

PRECISION

RESISTOR

TYPE PT/ST

6

CORP

2kΩ

31.6kΩ

dB OUTPU 100mV/dB

00828-030

V

IN

POWER

DOWN

C

8kΩ

1

2

3

INPUT

AMPLIFIER

FULL-WAVE

RECTIFIER

AD737

COM

8

7

6

499Ω

1kΩ

SCALE

FACT OR

+V

ADJUST

S

V

OUT

00828-031

Figure 31. DC-Coupled Offset Voltage and Scale Factor Trims

Rev. G | Page 17 of 24

AD737

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AD737 EVALUATION BOARD

An evaluation board, AD737-EVALZ, is available for experimenting or becoming familiar with rms-to-dc converters. Figure 32 is a photograph of the board; Figure 34 to Figure 37 s

how the signal and power plane copper patterns. The board is designed for multipurpose applications and can be used for the AD736 as well. Although not shipped with the board, an optional socket that accepts the 8lead surface mount package is available from Enplas Corp.

Figure 32. AD737 Evaluation Board

Figure 35. AD737 Evaluation B

00828-038

oard—Secondary-Side Copper

00828-034

Figure 33. AD737 Evaluation Board—Component-Side Silkscreen

As described in the Applications section, the AD737 may be connected in a variety of ways. As shipped, the board is configured for dual supplies with the high impedance input connected and the power-down feature disabled. Jumpers are provided for connecting the input to the low impedance input (Pin 1) and for dc connections to either input. The schematic with movable jumpers is shown in ne board is tested prior to shipment and only requires a power supply connection and a precision meter, to perform measurements. Tabl e 7 provides a bill of materials for the AD737 evaluation board.

Figure 38. The jumper positions in black are default con-

ctions; the dotted-outline jumpers are optional connections. The

00828-035

Figure 36. AD737 Evaluation Board—Internal Power Plane

00828-032

00828-036

Figure 37. AD737 Evaluation Board—Internal Ground Plane

Figure 34. AD737 Evaluation B

oard—Component-Side Copper

00828-033

Rev. G | Page 18 of 24

AD737

–V

V

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J1

GND1 GND3GND2 GND4

W1

DC

COUP

V

IN

C

IN

0.1µF

GND

P2 HI-Z SEL

IN

R1

1MΩ

FILT

NORM

W4

LO-Z IN

W2

PD

SEL

PIN3

C1

+

10µF

25V

LO-Z

HI-Z

1

C

2

V

3

POWER DOWN

4

–V

+

V

S

J3

–V

C4

0.1µF

Figure 38. AD737 Evaluation Board Schematic

Table 7. AD737 Evaluation Board Bill of Materials

Qty Name Description Reference Designator Manufacturer Mfg. Part Number

1 Test Loop Red +VS Components Corp. TP-104-01-02 1 Test Loop Green −VS Components Corp. TP-104-01-05 2 Capacitor Tantalum 10 μF, 25 V C1, C2 Nichicon F931E106MCC 3 Capacitor 0.1 μF, 16 V, 0603, X7R C4, C6, CIN KEMET C0603C104K4RACTU 1 Capacitor Tantalum 33 μF, 16V, 20%, 6032 CAV Nichicon F931C336MCC 5 Test Loop Purple CAV, HI-Z, LO-Z, VIN, V 1 Integrated Circuit RMS-to-DC converter DUT Analog Devices, Inc. AD737JRZ 4 Test Loop Black GND1, GND2, GND3, GND4 Components Corp. TP-104-01-00 2 Connector BNC, right angle J1, J2 AMP 227161-1 1 Header 6 Pins, 2 × 3 J3 3M 929836-09-03 1 Header 3 Pins P2 Molex 22-10-2031 1 Resistor 1 MΩ, 1/10 W, 1%, 0603 R1 Panasonic ERJ3EKF1004V 2 Resistor 0 Ω, 5%, 0603 R3, R4 Panasonic ERJ3GEY0R00V 4 Header 2 Pins, 0.1" center W1, W2, W3, W4 Molex 22-10-2021

S

–VS+V

W3

AC COUP

+

CC

DUT

AD737

C

IN

S

C

33µF

S

16V

C

+

S

COM

+V

OUTPUT

C

AV

+

F2

C2

+

10µF 25V

R3 0Ω

R4 0Ω

8

7

S

C6

0.1µF

6

5

AV

Components Corp. TP-104-01-07

OUT

+V

CAV

V

OUT

S

J2

C

F1

00828-037

Rev. G | Page 19 of 24

AD737

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OUTLINE DIMENSIONS

5.00 (0.1968)

4.80 (0.1890)

4.00 (0.1574)

3.80 (0.1497)

0.25 (0.0 098)

0.10 (0.0 040)

COPLANARI TY

0.10

CONTROL LING DI MENSIO NS ARE IN MILLI METERS; INCH DIMENS IONS (IN PARENTHESES) ARE ROUNDED-O FF MIL LIME TER EQUIVALENTS F OR REFERENCE O NLY AND ARE NOT APPROPRIATE FO R USE IN DESI GN.

85

1

1.27 (0.050 0)

SEATING

PLANE

COMPLI ANT TO JEDEC STANDARDS MS -012-A A

BSC

6.20 (0.2 440)

5.80 (0.2 284)

4

1.75 (0.0 688)

1.35 (0.0 532)

0.51 (0.0201)

0.31 (0.0122)

8° 0°

0.25 (0.0098)

0.17 (0.0067)

Figure 39. 8-Lead Standard Small Outline Package [SOIC_N]

Nar

row Body

(R-8)

Dimensions shown in millimeters and (inches)

0.50 (0.0196)

0.25 (0.0099)

1.27 (0.0500)

0.40 (0.0157)

45°

0.005 (0.13)

0.200 (5.08) MAX

0.200 (5.08)

0.125 (3.18)

0.023 (0.58)

0.014 (0.36)

CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FOR

060506-A

REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.

Figure 40. 8-Lead Ceramic Dual In-Line Package [CERDIP]

Dimensions shown in inches and (millimeters)

0.055 (1.40)

MIN

14

0.100 (2.54) BSC

0.405 (10.29) MAX

MAX

0.070 (1.78)

0.030 (0.76)

58

0.310 (7.87)

0.220 (5.59)

0.060 (1.52)

0.015 (0.38)

0.150 (3.81) MIN

SEATING PLANE

-8)

(Q

0.320 (8.13)

0.290 (7.37)

15°

0°

0.015 (0.38)

0.008 (0.20)

0.210 (5.33)

0.150 (3.81)

0.130 (3.30)

0.115 (2.92)

0.022 (0.56)

0.018 (0.46)

0.014 (0.36)

0.400 (10.16)

0.365 (9.27)

0.355 (9.02)

8

1

0.100 (2.54)

MAX

0.070 (1.78)

0.060 (1.52)

0.045 (1.14)

CONTROLL ING DIMENS IONS ARE IN INCHES; MILLIMETER DI MENSIONS (IN PARENTHESES) ARE ROUNDED-OF F INCH EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRI ATE FOR USE IN DES IGN. CORNER LEADS MAY BE CONFIGURED AS WHOL E OR HALF LEADS.

5

0.280 (7.11)

0.250 (6.35)

0.240 (6.10)

4

BSC

0.015 (0.38) MIN

SEATING PLANE

0.005 (0.13) MIN

COMPLIANT TO JEDEC STANDARDS MS-001

0.060 (1.52) MAX

0.015 (0.38) GAUGE

PLANE

0.325 (8.26)

0.310 (7.87)

0.300 (7.62)

0.430 (10.92) MAX

Figure 41. 8-Lead Plastic Dual-In-Line Package [PDIP]

(N-8)

Dim

ensions shown in inches and (millimeters)

0.195 (4.95)

0.130 (3.30)

0.115 (2.92)

0.014 (0.36)

0.010 (0.25)

0.008 (0.20)

070606-A

Rev. G | Page 20 of 24

AD737

www.BDTIC.com/ADI

ORDERING GUIDE

Model Temperature Range Package Description Package Option

AD737AN −40°C to +85°C 8-Lead Plastic Dual In-Line Package [PDIP] N-8 AD737ANZ AD737AQ −40°C to +85°C 8-Lead Ceramic Dual In-Line Package [CERDIP] Q-8 AD737AR −40°C to +85°C 8-Lead Standard Small Outline Package [SOIC_N] R-8 AD737ARZ AD737BQ −40°C to +85°C 8-Lead Ceramic Dual In-Line Package [CERDIP] Q-8 AD737JN 0°C to 70°C 8-Lead Plastic Dual In-Line Package [PDIP] N-8 AD737JNZ AD737JR 0°C to 70°C 8-Lead Standard Small Outline Package [SOIC_N] R-8 AD737JR-REEL 0°C to 70°C 8-Lead Standard Small Outline Package [SOIC_N] R-8 AD737JR-REEL7 0°C to 70°C 8-Lead Standard Small Outline Package [SOIC_N] R-8 AD737JR-5 0°C to 70°C 8-Lead Standard Small Outline Package [SOIC_N] R-8 AD737JR-5-REEL 0°C to 70°C 8-Lead Standard Small Outline Package [SOIC_N] R-8 AD737JR-5-REEL7 0°C to 70°C 8-Lead Standard Small Outline Package [SOIC_N] R-8 AD737JRZ AD737JRZ-R7 AD737JRZ-RL AD737JRZ-5 AD737JRZ-5-R7 AD737JRZ-5-RL AD737KN 0°C to 70°C 8-Lead Plastic Dual In-Line Package [PDIP] N-8 AD737KNZ AD737KR 0°C to 70°C 8-Lead Standard Small Outline Package [SOIC_N] R-8 AD737KR-REEL 0°C to 70°C 8-Lead Standard Small Outline Package [SOIC_N] R-8 AD737KR-REEL7 0°C to 70°C 8-Lead Standard Small Outline Package [SOIC_N] R-8 AD737KRZ AD737KRZ-RL AD737KRZ-R7 AD737-EVALZ

1

Z = Pb-free part.

1

−40°C to +85°C 8-Lead Plastic Dual In-Line Package [PDIP] N-8

−40°C to +85°C 8-Lead Standard Small Outline Package [SOIC_N] R-8

0°C to 70°C 8-Lead Plastic Dual In-Line Package [PDIP] N-8

0°C to 70°C 8-Lead Standard Small Outline Package [SOIC_N] R-8 0°C to 70°C 8-Lead Standard Small Outline Package [SOIC_N] R-8 0°C to 70°C 8-Lead Standard Small Outline Package [SOIC_N] R-8 0°C to 70°C 8-Lead Standard Small Outline Package [SOIC_N] R-8

1

0°C to 70°C 8-Lead Standard Small Outline Package [SOIC_N] R-8

1

0°C to 70°C 8-Lead Standard Small Outline Package [SOIC_N] R-8

0°C to 70°C 8-Lead Plastic Dual In-Line Package [PDIP] N-8

0°C to 70°C 8-Lead Standard Small Outline Package [SOIC_N] R-8 0°C to 70°C 8-Lead Standard Small Outline Package [SOIC_N] R-8 0°C to 70°C 8-Lead Standard Small Outline Package [SOIC_N] R-8 Evaluation Board

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AD737

www.BDTIC.com/ADI

NOTES

Rev. G | Page 22 of 24

AD737

www.BDTIC.com/ADI

NOTES

Rev. G | Page 23 of 24

AD737

www.BDTIC.com/ADI

NOTES

Rev. G | Page 24 of 24

Datasheet AD737 Datasheet (ANALOG DEVICES)

Specifications and Main Features

Frequently Asked Questions

User Manual

FEATURES

GENERAL DESCRIPTION

FUNCTIONAL BLOCK DIAGRAM

PRODUCT HIGHLIGHTS

TABLE OF CONTENTS

REVISION HISTORY

SPECIFICATIONS

ABSOLUTE MAXIMUM RATINGS

THERMAL RESISTANCE

ESD CAUTION

PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS

TYPICAL PERFORMANCE CHARACTERISTICS

THEORY OF OPERATION

TYPES OF AC MEASUREMENT

DC ERROR, OUTPUT RIPPLE, AND AVERAGING ERROR

AC MEASUREMENT ACCURACY AND CREST FACTOR

CALCULATING SETTLING TIME

APPLICATIONS

RAPID SETTLING TIMES VIA THE AVERAGE RESPONDING CONNECTION

SELECTING PRACTICAL VALUES FOR CAPACITORS

SCALING INPUT AND OUTPUT VOLTAGES

Extending or Scaling the Input Range

Battery Operation

Scaling the Output Voltage

AD737 EVALUATION BOARD

OUTLINE DIMENSIONS

ORDERING GUIDE