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a FEATURES Low Cost A-D Conversion Versatile Input Amplifier Positive or Negative Voltage Modes Negative Current Mode High Input Impedance, Low Drift Single Supply, 5 V to 36 V Linearity: ؎0.05% FS 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

PRODUCT DESCRIPTION

The AD537 is a monolithic V-F converter consisting of an input amplifier, a precision oscillator system, an accurate internal reference 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 overall 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-tofrequency 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 TO-116 ceramic DIP or a TO-100 metal can; both are hermetically sealed packages. *Protected by Patent Nos. 3,887,963 and RE 30,586.

Integrated Circuit Voltage-to-Frequency Converter AD537* PIN CONFIGURATIONS “D” Package (TO-116) “H” Package (TO-100) LOGIC GND 10

AD537 LOGIC GND

1

SYNC

2

IIN

–VIN 14

DRIVER

3

13

+VS

12 CURRBUF TO-FREQ CONV

1

OUTPUT

–VIN

4

11

8 +VS

2

CAP

5

10

VOS

VTEMP

6

VT

9

VOS

VREF

7

VR

8

–VS

OUTPUT

DRIVER +VIN

CAP

+VIN

BUF 3

CURRTO-FREQ CONV 7

VT

PRECISION VOLTAGE VR REFERENCE

VTEMP PRECISION VOLTAGE REFERENCE

9

AD537

4 VREF

CAP

6 5

CAP

–VS (CONNECTED TO CASE)

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 external RC timing network to set the desired full-scale frequency and a selectable pull-up resistor for the open collector output stage. Any full-scale input voltage range from 100 mV to 10 volts (or greater, depending on +VS) can be 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. 2. The power supply requirements are minimal, only 1.2 mA 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 (+VS – 4) volts. Negative inputs can easily be connected for below ground operation. 3. F-V converters with excellent characteristic are also easy to build by connecting the AD537 in a phase-locked loop. Application particulars are shown in Figure 6. 4. The versatile open-collector NPN output stage can sink up to 20 mA with a saturation voltage less than 0.4 volts. The Logic Common terminal can be connected to any level between ground (or –VS) and 4 volts below +VS. This allows easy direct interface to any logic family with either positive or negative logic levels. 5. The AD537 is available in versions compliant with MILSTD-883. Refer to the Analog Devices Military Product Databook or current AD537/883B data sheet for detailed specifications.

REV. B 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: 617/329-4700 Fax: 617/326-8703


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