AD652SW AD [Analog Devices], AD652SW Datasheet

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AD652SW

Manufacturer Part Number
AD652SW
Description
Monolithic Synchronous Voltage-to-Frequency Converter
Manufacturer
AD [Analog Devices]
Datasheet
a
PRODUCT DESCRIPTION
The AD652 Synchronous Voltage-to-Frequency Converter
(SVFC) is a powerful building block for precision analog-to-
digital conversion, offering typical nonlinearity of 0.002%
(0.005% maximum) at a 100 kHz output frequency. The inher-
ent monotonicity of the transfer function and wide range of
clock frequencies allows the conversion time and resolution to
be optimized for specific applications.
The AD652 uses a variation of the popular charge-balancing
technique to perform the conversion function. The AD652 uses
an external clock to define the full-scale output frequency,
rather than relying on the stability of an external capacitor. The
result is a more stable, more linear transfer function, with sig-
nificant application benefits in both single- and multichannel
systems.
Gain drift is minimized using a precision low drift reference and
low TC on-chip thin-film scaling resistors. Furthermore, the ini-
tial gain error is reduced to less than 0.5% by the use of
laser-wafer-trimming.
The analog and digital sections of the AD652 have been de-
signed to allow operation from a single-ended power source,
simplifying its use with isolated power supplies.
The AD652 is available in five performance grades. The 20-lead
PLCC packaged JP and KP grades are specified for operation
over the 0°C to +70°C commercial temperature range. The
16-lead cerdip-packaged AQ and BQ grades are specified for
operation over the –40°C to +85°C industrial temperature
range, and the AD652SQ is available for operation over the full
–55°C to +125°C extended temperature range.
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.
FEATURES
Full-Scale Frequency (Up to 2 MHz) Set by External
Extremely Low Linearity Error (0.005% max at 1 MHz
No Critical External Components Required
Accurate 5 V Reference Voltage
Low Drift (25 ppm/ C max)
Dual or Single Supply Operation
Voltage or Current Input
MIL-STD-883 Compliant Versions Available
System Clock
FS, 0.02% max at 2 MHz FS)
Voltage-to-Frequency Converter
PRODUCT HIGHLIGHTS
1. The use of an external clock to set the full-scale frequency
2. The AD652 Synchronous VFC requires only a single external
3. The AD652 includes a buffered, accurate 5 V reference
4. The clock input of the AD652 is TTL and CMOS compat-
5. The AD652 can also be configured for use as a synchronous
6. The AD652 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
allows the AD652 to achieve linearity and stability far supe-
rior to other monolithic VFCs. By using the same clock to
drive the AD652 and (through a suitable divider) also set the
counting period, conversion accuracy is maintained indepen-
dent of variations in clock frequency.
component (a noncritical integrator capacitor) for operation.
which is available to the user.
ible and can also be driven by sources referred to the negative
power supply. The flexible open-collector output stage pro-
vides sufficient current sinking capability for TTL and CMOS
logic, as well as for optical couplers and pulse transformers.
A capacitor-programmable one-shot is provided for selection
of optimum output pulse width for power reduction.
F/V converter for isolated analog signal transmission.
STD-883. Refer to the Analog Devices Military Products
Databook or current AD652/883B data sheet for detailed
specifications.
FUNCTIONAL BLOCK DIAGRAM
Monolithic Synchronous
World Wide Web Site: http://www.analog.com
© Analog Devices, Inc., 2000
AD652

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AD652SW Summary of contents

Page 1

FEATURES Full-Scale Frequency ( MHz) Set by External System Clock Extremely Low Linearity Error (0.005% max at 1 MHz FS, 0.02% max at 2 MHz FS) No Critical External Components Required Accurate 5 V Reference Voltage Low ...

Page 2

AD652–SPECIFICATIONS Parameter VOLTAGE-TO-FREQUENCY MODE Gain Error f = 200 kHz CLOCK MHz CLOCK MHz CLOCK Gain Temperature Coefficient f = 200 kHz CLOCK MHz CLOCK MHz CLOCK Power ...

Page 3

Parameter OUTPUT STAGE mA) OL OUT <0 <0 –T OL MIN MAX I (Off Leakage) OH Delay Time, Positive Clock Edge to Output Pulse Fall Time (Load = ...

Page 4

AD652 ORDERING GUIDE Gain Drift Specified Part ppm MHz Temperature Package 1 Number 100 kHz Linearity % Range C AD652JP 50 max 0.02 max 0 to +70 AD652KP 25 max 0.005 max 0 to +70 AD652AQ 50 max ...

Page 5

Figure 2. AD652 Block Diagram and System Waveforms Referring to Figure 2, it can ...

Page 6

AD652 The result of this synchronism is that the rate at which data may be extracted from the series bit stream produced by the SVFC is limited. The output pulses are typically counted during a fixed gate interval and the ...

Page 7

Option #4 provides the closest to the ideal transfer function as diagrammed in Figure 8b. Figure 8c shows the effects on the transfer relation of the other three options. In the first case, the slope of the transfer function is ...

Page 8

AD652 adjustment is then accomplished using a 500 Ω series trimmer. See Figures 10a and 10b. When negative input voltages are used, this 500 Ω trimmer will be tied to ground and Pin 6 will be the input pin. This ...

Page 9

DIGITAL GROUND Digital Ground can be at any potential between –V –4 volts). This can be very useful in a system with derived grounds rather than stiff supplies. For example small iso- lated power circuit, often only a ...

Page 10

AD652 In Figure 17 the “+” input is tied to a 1.2 V reference and low level TTL pulses are used as the frequency input. The pulse must be low on the falling edge of the clock. On the subsequent ...

Page 11

Figure 18. Frequency Output Multiplier This 1 MHz full-scale frequency is then used as the clock input to the AD652 SVFC. Since the AD652 full-scale output fre- quency is one-half the clock frequency, the 1 MHz FS clock frequency establishes ...

Page 12

AD652 Figure 22. RS-422 Standard Data Transmission the output with an external transistor. The width of this sync pulse is shorter than the width of the frequency output pulses to facilitate decoding the signal. The RC lag network on the ...

Page 13

SVFC Demultiplexer The demultiplexer needed to separate the combined signals is shown in Figure 23. A phase locked loop drives another four phase clock chip to lock onto the reconstructed clock signal. The sync pulses are distinguished from the data ...

Page 14

AD652 Figure 26. Demultiplexer Frequency-to-Voltage Conversion Analog Signal Reconstruction desired to reconstruct the analog voltages from the multi- plex signal, then three more AD652 SVFC devices are used as frequency-to-voltage converters, as shown in Figure 26. The ...

Page 15

D-flop. The chopper frequency is generated from an AD654 VFC and is frequency divided by two to develop differential drive for the chopper transistors, and to ensure an accurate 50 percent duty cycle. The ...

Page 16

AD652 Figure 30. Delta Modulator lnput Signal and Ramp-Wise Approximation Figure 31. Delta Modulator Input Signal, Ramp-Wise Approximation and Output Frequency Figure 32. Maximum Integrating Cap Value vs. Input Signal Bandwidth BRIDGE TRANSDUCER INTERFACE The circuit of Figure 33 illustrates ...

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