ANALOG DEVICES AD650 Service Manual

Voltage-to-Frequency and

C

FEATURES

V/F conversion to 1 MHz
Reliable monolithic construction
Very low nonlinearity

0.002% typ at 10 kHz

0.005% typ at 100 kHz

0.07% typ at 1 MHz
Input offset trimmable to zero
CMOS- or TTL-compatible
Unipolar, bipolar, or differential V/F
V/F or F/V conversion
Available in surface mount
MIL-STD-883 compliant versions available

PRODUCT DESCRIPTION

The AD650 V/F/V (voltage-to-frequency or frequency-to-voltage
converter) provides a combination of high frequency operation
and low nonlinearity previously unavailable in monolithic form.
The inherent monotonicity of the V/F transfer function makes
the AD650 useful as a high-resolution analog-to-digital converter.
A flexible input configuration allows a wide variety of input
voltage and current formats to be used, and an open-collector
output with separate digital ground allows simple interfacing to
either standard logic families or opto-couplers.

The linearity error of the AD650 is typically 20 ppm (0.002% of
full scale) and 50 ppm (0.005%) maximum at 10 kHz full scale.
This corresponds to approximately 14-bit linearity in an analog­to-digital converter circuit. Higher full-scale frequencies or
longer count intervals can be used for higher resolution
conversions. The AD650 has a useful dynamic range of six
decades allowing extremely high resolution measurements.
Even at 1 MHz full scale, linearity is guaranteed less than
1000 ppm (0.1%) on the AD650KN, BD, and SD grades.

In addition to analog-to-digital conversion, the AD650 can be
used in isolated analog signal transmission applications,
phased-locked loop circuits, and precision stepper motor speed
controllers. In the F/V mode, the AD650 can be used in
precision tachometer and FM demodulator circuits.

The input signal range and full-scale output frequency are user­programmable with two external capacitors and one resistor.
Input offset voltage can be trimmed to zero with an external
potentiometer.

Frequency-to-Voltage Converter

AD650

FUNCTIONAL BLOCK DIAGRAM

V

1

OUT

+IN

–IN

BIPOLAR

OFFSET

CURRENT

–V

ONE

SHOT

APACITOR

NC

2

3

4

–V

S

5

S

OUT

FREQ

6

7

NC = NO CONNECT

OP

AMP

ONE

SHOT

IN

OUT

–V

INPUT

OFFSET

TRIM

S1

1mA

–0.6V

S

COMP

Figure 1.

The AD650JN and AD650KN are offered in plastic 14-lead DIP
packages. The AD650JP is available in a 20-lead plastic leaded
chip carrier (PLCC). Both plastic packaged versions of the
AD650 are specified for the commercial temperature range
(0°C to 70°C). For industrial temperature range (−25°C to
+85°C) applications, the AD650AD and AD650BD are offered
in ceramic packages. The AD650SD is specified for the full

−55°C to +125°C extended temperature range.

PRODUCT HIGHLIGHTS

1. Can operate at full-scale output frequencies up to 1 MHz

(in addition to having very high linearity).

2. Can be configured to accommodate bipolar, unipolar, or

differential input voltages, or unipolar input currents.

3. TTL or CMOS compatibility is achieved by using an open

collector frequency output. The pull-up resistor can be
connected to voltages up to 30 V.

4. The same components used for V/F conversion can also be

used for F/V conversion by adding a simple logic biasing
network and reconfiguring the AD650.

5. Separate analog and digital grounds prevent ground loops

in real-world applications.

6. Available in versions compliant with MIL-STD-883.

AD650

OFFSET

14

NULL

OFFSET

13

NULL

+V

12

S

ANALOG

11

GND

DIGITAL

10

GND

COMPARATOR

9

INPUT

F

8

OUTPUT

00797-001

Rev. D

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
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Trademarks and registered trademarks are the property of their respective owners.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone] www.analog.com
Fax: [phone] ©2006 Analog Devices, Inc. All rights reserved.

AD650

TABLE OF CONTENTS

Features.............................................................................................. 1

F/V Conversion .......................................................................... 10

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

Product Description......................................................................... 1

Product Highlights ........................................................................... 1

Revision History ............................................................................... 2

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

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

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

Pin Configurations and Function Descriptions ........................... 6

Circuit Operation ............................................................................. 7

Unipolar Configuration............................................................... 7

Component Selection................................................................... 8

Bipolar V/F.................................................................................. 10

Unipolar V/F, Negative Input Voltage ..................................... 10

REVISION HISTORY

High Frequency Operation....................................................... 10

Decoupling and Grounding...................................................... 12

Temperature Coefficients .......................................................... 12

Nonlinearity Specification ........................................................ 13

PSRR............................................................................................. 14

Other Circuit Considerations................................................... 14

Applications..................................................................................... 16

Differential Voltage-to-Frequency Conversion...................... 16

Autozero Circuit......................................................................... 16

Phase-Locked Loop F/V Conversion ...................................... 17

Outline Dimensions....................................................................... 19

Ordering Guide .......................................................................... 20

3/06—Rev. C to Rev. D

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

Changes to Product Highlights....................................................... 1

Changes to Table 1............................................................................ 3

Added Pin Function Descriptions Table ...................................... 6

Updated Outline Dimensions....................................................... 18

Changes to Ordering Guide.......................................................... 19

Rev. D | Page 2 of 20

AD650

SPECIFICATIONS

T = 25°C, VS = ±15 V, unless otherwise noted.

Table 1.

AD650J/AD650A AD650K/AD650B AD650S
Model Min Typ Max Min Typ Max Min Typ Max Units

DYNAMIC PERFORMANCE

Full-Scale Frequency Range 1 1 1 MHz
Nonlinearity

f
f
f
f

Full-Scale Calibration Error

100 kHz ± 5 ± 5 ± 5 %
1 MHz ± 10 ± 10 ± 10 %

vs. Supply
vs. Temperature

BIPOLAR OFFSET CURRENT

Activated by 1.24 kΩ Between

Pin 4 and Pin 5

DYNAMIC RESPONSE

Maximum Settling Time for

Full-Scale Step Input

Overload Recovery Time

Step Input

ANALOG INPUT AMPLIFIER

(V/F CONVERSION)

Current Input Range (Figure 4) 0 +0.6 0 +0.6 0 +0.6 mA
Voltage Input Range (Figure 12) −10 0 −10 0 −10 0 V
Differen tial Impedance 2 MΩ||10 pF 2 MΩ||10 pF 2 MΩ||10 pF
Common-Mode Impedance 1000 MΩ||10 pF 1000 MΩ||10 pF 1000 MΩ||10 pF
Input Bias Current

Noninverting Input 40 100 40 100 40 100 nA
Inverting Input ±8 ±20 ±8 ±20 ±8 ±20 nA

Input Offset Voltage

(Trimmable to Zero) ±4 ±4 ±4 mV
vs. Temperature (T

Safe Input Voltage ±VS ±VS ±VS V

COMPARATOR (F/V CONVERSION)

Logic 0 Level −VS −1 −VS −1 −VS −1 V
Logic 1 Level 0 +VS 0 +VS 0 +VS V
Pulse Width Range4 0.1 (0.3 × tOS) 0.1 (0.3 × tOS) 0.1 (0.3 × tOS) µs
Input Impedance 250 250 250 kΩ

OPEN COLLECTOR OUTPUT

(V/F CONVERSION)
Output Voltage in Logic 0

I
Output Leakage Current in Logic 1 100 100 100 nA
Voltage Range5 0 36 0 36 0 36 V

1

= 10 kHz 0.002 0.005 0.002 0.005 0.002 0.005 %

MAX

= 100 kHz 0.005 0.02 0.005 0.02 0.005 0.02 %

MAX

= 500 kHz 0.02 0.05 0.02 0.05 0.02 0.05 %

MAX

= 1 MHz 0.1 0.05 0.1 0.05 0.1 %

MAX

3

2

% of

−0.015 +0.015 −0.015 +0.015 −0.015 +0.015

FSR/V

A, B, and S Grades

at 10 kHz ±75 ±75 ±75 ppm/°C
at 100 kHz ±150 ±150 ±200 ppm/°C

J and K Grades

at 10 kHz ±75 ±75 ppm/°C
at 100 kHz ±150 ±150 ppm/°C

0.45 0.5 0.55 0.45 0.5 0.55 0.45 0.5 0.55 mA

1 pulse of new frequency plus 1 s 1 pulse of new frequency plus 1 s 1 pulse of new frequency plus 1 s

1 pulse of new frequency plus 1 s 1 pulse of new frequency plus 1 s 1 pulse of new frequency plus 1 s

to T

MIN

) ±30 ±30 ±30 µV/°C

MAX

≤ 8 mA, T

SINK

MIN

to T

0.4 0.4 0.4 V

MAX

Rev. D | Page 3 of 20

AD650

AD650J/AD650A AD650K/AD650B AD650S
Model Min Typ Max Min Typ Max Min Typ Max Units

AMPLIFIER OUTPUT (F/V CONVERSION)

Voltage Range

(1500 Ω Min Load Resistance)

Source Current

(750 Ω Max Load Resistance)

Capacitive Load

(Without Oscillation)

POWER SUPPLY

Voltage, Rated Performance ±9 ±18 ±9 ±18 ±9 ±18 V
Quiescent Current 8 8 8 mA

TEMPERATURE RANGE

Rated Performance

N Package 0 +70 0 +70 °C
D Package −25 +85 −25 +85 −55 +125 °C

1

Nonlinearity is defined as deviation from a straight line from zero to full scale, expressed as a fraction of full scale.

2

Full-scale calibration error adjustable to zero.

3

Measured at full-scale output frequency of 100 kHz.

4

Refer to F/V conversion section of the text.

5

Referred to digital ground.

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. All min

and max specifications are guaranteed, although only those shown in boldface are tested on all production units.

0 10 0 10 0 10 V

10 10 10 mA

100 100 100 pF

Rev. D | Page 4 of 20

AD650

ABSOLUTE MAXIMUM RATINGS

Parameter Rating

Total Supply Voltage 36 V
Storage Temperature Range −55°C to +150°C
Differential Input Voltage ±10 V
Maximum Input Voltage ±VS
Open Collector Output Voltage

Above Digital GND

Current 50 mA
Amplifier Short Circuit to Ground Indefinite
Comparator Input Voltage ±VS

36 V

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.

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.

Rev. D | Page 5 of 20

AD650

PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS

1

V

OUT

2

+IN

–IN

3

BIBOLAR OFF SET

CURRENT

–V

ONE SHOT

CAPACITOR

AD650

TOP VIEW

4

(Not to Scale)

5

S

6

7

NC

NC = NO CONNECT

Figure 2. D-14, N-14 Pin Configurations

Table 2. Pin Function Descriptions

Pin No.

D-14, N-14 P-20A Mnemonic Description

1 2 V

2 3 +IN Positive Analog Input.
3 4 –IN Negative Analog Input.
4 6

5 8 –VS Negative Power Supply Input.
6 9

7 1, 5, 7, 10, 11, 15, 17 NC No Connect.
8 12 F
9 13 COMPARATOR INPUT

10 14 DIGITAL GND Digital Ground.
11 16 ANALOG GND Analog Ground.
12 18 +VS Positive Power Supply Input.
13, 14 19, 20 OFFSET NULL

OFFSET NULL

14

13

OFFSET NULL

12

+V

S

ANALOG GND

11

DIGITAL GND

10

COMPARATOR

9

INPUT

8

F

OUTPUT

00797-010

NC = NO CONNECT

OUT

Output of Operational Amplifier. The operational amplifier, along with C
is used in the integrate stage of the V to F conversion.

BIPOLAR OFFSET
CURRENT

ONE-SHOT
CAPACITOR

Frequency Output from AD650.

OUTPUT

On-Chip Current Source. This can be used in conjunction with an external
resistor to remove the operational amplifier’s offset.

The Capacitor, C

OS

for the one shot.

Input to Comparator. When the input voltage reaches −0.6 V, the one shot is
triggered.

Offset Null Pins. Using an external potentiometer, the offset of the
operational amplifier can be removed.

BIPOLAR O FFSET

CURRENT

, is Connected to This Pin. COS determines the time period

OUT

+IN

V

NC

OFFSET

NULL

OFFSET

NC

NULL

18

17

16

15

14

INPUT

OUTPUT

F

COMPARATOR

–V

–IN

NC

NC

4

5

6

7

8

S

1201923

PIN 1
INDENTFIER

AD650

TOP VIEW

(Not to scale)

91011 12 13

NC

ONE SHOT

CAPACITOR

Figure 3. P-20A Pin Configuration

+V

S

NC

ANALOG GND

NC

DIGITAL GND

00797-011

,

INT

Rev. D | Page 6 of 20