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)
MIL-STD-883 Compliant Versions Available
LOGIC GND 1
13 +VS +VIN 2
(CONNECTED TO CASE)
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
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
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.
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.
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.
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. 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. Ap-
plication 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 be-
tween 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 MIL-
STD-883. Refer to the Analog Devices Military Product
Databook or current AD537/883B data sheet for detailed
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