AD537 Analog Devices, Inc., AD537 Datasheet

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AD537

Manufacturer Part Number
AD537
Description
Integrated Circuit Voltage-to-frequency Converter
Manufacturer
Analog Devices, Inc.
Datasheet

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PRODUCT DESCRIPTION
The AD537 is a monolithic V-F converter consisting of an input
amplifier, a precision oscillator system, an accurate internal ref-
erence generator and a high current output stage. Only a single
external RC network is required to set up any full-scale (F.S.)
frequency up to 100 kHz and any F.S. input voltage up to
± 30 V. Linearity error is as low as ± 0.05% for 10 kHz F.S., and
operation is guaranteed over an 80 dB dynamic range. The over-
all temperature coefficient (excluding the effects of external
components) is typically ± 30 ppm/°C. The AD537 operates
from a single supply of 5 V to 36 V and consumes only 1.2 mA
quiescent current.
A temperature-proportional output, scaled to 1.00 mV/K,
enables the circuit to be used as a reliable temperature-to-
frequency converter; in combination with the fixed reference
output of 1.00 V, offset scales such as 0°C or 0°F can be generated.
The low drift (1 µV/°C typ) input amplifier allows operation
directly from small signals (e.g., thermocouples or strain gages)
while offering a high (250 MΩ) input resistance. Unlike most
V–F converters, the AD537 provides a square-wave output, and
can drive up to 12 TTL loads, LEDs, very long cables, etc.
The excellent temperature characteristics and long-term stability
of the AD537 are guaranteed by the primary bandgap reference
generator and the low T.C. silicon chromium thin film resistors
used throughout.
The device is available in either a 14-lead ceramic DIP or a 10-lead
metal can; both are hermetically sealed packages.
*Protected by Patent Nos. 3,887,963 and RE 30,586.
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.
FEATURES
Low Cost A–D Conversion
Versatile Input Amplifier
Single Supply, 5 V to 36 V
Linearity:
Low Power: 1.2 mA Quiescent Current
Full-Scale Frequency up to 100 kHz
1.00 V Reference
Thermometer Output (1 mV/K)
F-V Applications
MIL-STD-883 Compliant Versions Available
Positive or Negative Voltage Modes
Negative Current Mode
High Input Impedance, Low Drift
0.05% FS
Voltage-to-Frequency Converter
The AD537 is available in three performance/temperature
grades; the J and K grades are specified for operation over the
0°C to +70°C range while the AD537S is specified for operation
over the extended temperature range, –55°C to +125°C.
PRODUCT HIGHLIGHTS
1. The AD537 is a complete V-F converter requiring only an
2. The power supply requirements are minimal, only 1.2 mA
3. F-V converters with excellent characteristic are also easy to
4. The versatile open-collector NPN output stage can sink up
5. The AD537 is available in versions compliant with MIL-
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
Fax: 781/326-8703
LOGIC GND
external RC timing network to set the desired full-scale fre-
quency and a selectable pull-up resistor for the open collec-
tor output stage. Any full-scale input voltage range from
100 mV to 10 volts (or greater, depending on +V
accommodated by proper selection of timing resistor. The
full-scale frequency is then set by the timing capacitor from
the simple relationship, f = V/10RC.
quiescent current is drawn from a single positive supply from
4.5 volts to 36 volts. In this mode, positive inputs can vary
from 0 volts (ground) to (+V
easily be connected for below ground operation.
build by connecting the AD537 in a phase-locked loop. Ap-
plication particulars are shown in Figure 6.
to 20 mA with a saturation voltage less than 0.4 volts. The
Logic Common terminal can be connected to any level be-
tween ground (or –V
easy direct interface to any logic family with either positive or
negative logic levels.
STD-883. Refer to the Analog Devices Military Product
Databook or current AD537/883B data sheet for detailed
specifications.
V
SYNC
V
TEMP
–V
+V
REF
I
IN
IN
IN
1
2
3
4
5
6
7
D-14 Package
V
V
R
T
BUF
REFERENCE
PRECISION
VOLTAGE
PIN CONFIGURATIONS
TO-FREQ
DRIVER
AD537
CURR-
CONV
World Wide Web Site: http://www.analog.com
S
) and 4 volts below +V
14
13
12
11
10
9
8
Integrated Circuit
OUTPUT
+V
CAP
CAP
V
V
–V
OS
OS
S
S
S
– 4) volts. Negative inputs can
+V
V
TEMP
IN
3
2
© Analog Devices, Inc., 2000
–V
V
IN
REF
H-10A Package
(CONNECTED TO CASE)
1
4
BUF
AD537
V
V
AD537*
T
R
REFERENCE
PRECISION
VOLTAGE
S
–V
10
. This allows
TO-FREQ
5
DRIVER
S
CURR-
CONV
S
) can be
LOGIC GND
9
6
CAP
OUTPUT
8
7
CAP
+V
S

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AD537 Summary of contents

Page 1

... AD537S is specified for operation over the extended temperature range, –55°C to +125°C. PRODUCT HIGHLIGHTS 1. The AD537 is a complete V-F converter requiring only an external RC timing network to set the desired full-scale fre- quency and a selectable pull-up resistor for the open collec- tor output stage ...

Page 2

... Temperature reference output performance is specified from 0°C to +70°C for “J” and “K” devices, –55°C to +125°C for “S” model Ceramic DIP Hermetic Metal Can. For outline information see Package Information section. 7 For AD537/883B specifications, refer to Analog Devices Military Products Databook. Specifications subject to change without notice. (typical @ +25 C with V (total unless otherwise noted) ...

Page 3

... CIRCUIT OPERATION Block diagrams of the AD537 are shown above. A versatile operational amplifier (BUF) serves as the input stage; its pur- pose is to convert and scale the input voltage signal to a drive current in the NPN follower. Optimum performance is achieved when, at the full-scale input voltage drive current is delivered to the current-to-frequency converter ...

Page 4

... The most sensitive nodes (besides the inputs) are the capacitor terminals and the SYNC pin. The timing capacitor should be located as close as possible to the AD537 to minimize signal pickup in the leads. In some cases, guard rings or shield- ing may be required. The SYNC pin should be decoupled through a 0.005 µ ...

Page 5

... The stage limits the output current at 25 mA; it can handle this limit indefinitely without damaging the device. REV. C Figure 5 shows the AD537 with a standard 0 to +10 volt input connection and the output stage connections. The values for the logic common voltage, pull-up resistor, positive logic level, and – ...

Page 6

... AD537 F-V CONVERTERS The AD537 can be used as a high linearity VCO in a phase- locked loop to accomplish frequency-to-voltage conversion. By operating the loop without a low-pass filter in the feedback path (first-order system), it can lock to any frequency from zero to an upper limit determined by the design, responding in three or four cycles to a step change of input frequency ...

Page 7

... Figure 13 which shows the response to an input rms 1 kHz sinusoid plus 1 V rms Gaussian noise. The positive supply to the AD537 is reduced by about order to keep the voltages at Pins 11 and 12 within the common-mode range of the AD534. Since this is also a first-order loop the circuit possesses a very wide capture range ...

Page 8

... This small amount of voltage can be introduced without an additional calibration step using the +1.00 V output of the AD537. To adjust the scale, the thermocouple should be raised to a known reference tempera- ture near 500°C and the frequency adjusted to value using R1. ...

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