AD694AR ,4.20 mA TransmitterCHARACTERISTICSV @ 2.5 mA 0.35 0.35 VCE(SAT)Leakage Current 61 61 μAAlarm Pin Current (Pin 10) 20 2 ..
AD694AR ,4.20 mA TransmitterFEATURES4–20 mA, 0–20 mA Output RangesPrecalibrated Input Ranges: 0 V to 2 V, 0 V to 10 VPrecisio ..
AD694BQ ,4.20 mA Transmittera4–20 mA TransmitterAD694*FUNCTIONAL BLOCK DIAGRAM
AD694BRZ , 4–20 mA Transmitter
AD694JN ,4.20 mA TransmitterFEATURES4–20 mA, 0–20 mA Output RangesPrecalibrated Input Ranges: 0 V to 2 V, 0 V to 10 VPrecisio ..
AD698 ,Universal LVDT Signal ConditionerFEATURES FUNCTIONAL BLOCK DIAGRAMSingle Chip Solution, Contains Internal Oscillator andVoltage Refe ..
ADC104S021CIMM/NOPB ,4 Channel, 50 ksps to 200 ksps, 10-Bit A/D Converter 10-VSSOP FEATURES DESCRIPTIONThe ADC104S021/ADC104S021Q is a low-power,2• Specified over a Range of Sample R ..
ADC1061CIN ,10-Bit High Speed µP-Compatible A/D Converter with Track/Hold FunctionApplicationsby an internal sampling circuit. Input signals at frequenciesn Waveform digitizersfrom ..
ADC1061CIWM ,10-Bit High Speed µP-Compatible A/D Converter with Track/Hold FunctionPin DescriptionsSymbol FunctionDV , These are the digital and analog positive supply voltage inputs ..
ADC10662CIWM ,10-Bit 360 ns A/D Converter with Input Multiplexer and Sample/Hold [Not recommended for new designs]Applicationssample-and-hold circuit.n Digital signal processor front endsThe ADC10662 and ADC10664 ..
ADC10662CIWM ,10-Bit 360 ns A/D Converter with Input Multiplexer and Sample/Hold [Not recommended for new designs]Featuresn Built-in sample-and-hold*Using an innovative, patented multistep conversion tech-nique, t ..
ADC10664CIN ,10-Bit 360 ns A/D Converter with Input Multiplexer and Sample/HoldFeaturesn Built-in sample-and-hold*Using an innovative, patented multistep conversion tech-nique, t ..
AD694AQ-AD694AR-AD694BQ-AD694JN
4.20 mA Transmitter
FUNCTIONAL BLOCK DIAGRAMREV. A
4–20 mA Transmitter
FEATURES
4–20 mA, 0–20 mA Output Ranges
Precalibrated Input Ranges:
0 V to 2 V, 0 V to 10 V
Precision Voltage Reference
Programmable to 2.000 V or 10.000 V
Single or Dual Supply Operation
Wide Power Supply Range: +4.5 V to +36 V
Wide Output Compliance
Input Buffer Amplifier
Open-Loop Alarm
Optional External Pass Transistor to Reduce
Self-Heating Errors
0.002% typ Nonlinearity
PRODUCT DESCRIPTIONThe AD694 is a monolithic current transmitter that accepts
high level signal inputs to drive a standard 4–20 mA current
loop for the control of valves, actuators, and other devices com-
monly used in process control. The input signal is buffered by
an input amplifier that can be used to scale the input signal or
buffer the output from a current mode DAC. Precalibrated in-
put spans of 0 V to 2 V and 0 V to 10 V are selected by simple
pin strapping; other spans may be programmed with external
resistor.
The output stage compliance extends to within 2 V of VS and its
special design allows the output voltage to extend below com-
mon in dual supply operation. An alarm warns of an open 4-to-
20 mA loop or noncompliance of the output stage.
Active laser trimming of the AD694’s thin film resistors results
in high levels of accuracy without the need for additional adjust-
ments and calibration. An external pass transistor may be used
with the AD694 to off-load power dissipation, extending the
temperature range of operation.
The AD694 is the ideal building block for systems requiring
noise immune 4–20 mA signal transmission to operate valves,
actuators, and other control devices, as well as for the transmis-
sion of process parameters such as pressure, temperature, or
flow. It is recommended as a replacement for discrete designs in
a variety of applications in industrial process control, factory
automation, and system monitoring.
The AD694 is available in hermetically sealed, 16-pin cerdip
and plastic SOIC, specified over the –40°C to +85°C industrial
temperature range, and in a 16-pin plastic DIP, specified over
the 0°C to +70°C temperature range.
*. Patents: 30,586; 4,250,445; 4,857,862.
PRODUCT HIGHLIGHTS1. The AD694 is a complete voltage in to 4–20 mA out current
transmitter.
2. Pin programmable input ranges are pre-calibrated at 0 V to
2 V and 0 V to 10 V.
3. The input amplifier may be configured to buffer and scale the
input voltage, or to serve as an output amplifier for current
output DACs.
4. The output voltage compliance extends to within 2 V of the
positive supply and below common. When operated with a
5 V supply, the output voltage compliance extends 30 V be-
low common.
5. The AD694 interfaces directly to 8-, 10-, and 12-bit single
supply CMOS and bipolar DACs.
6. The 4 mA zero current may be switched on and off with a
TTL control pin, allowing 0–20 mA operation.
7. An open collector alarm warns of loop failure due to open
wires or noncompliance of the output stage.
8. A monitored output is provided to drive an external pass
transistor. The feature off-loads power dissipation to extend
the temperature range of operation and minimize self-heating
error.
AD694–SPECIFICATIONSINPUT CHARACTERISTICS
OUTPUT CHARACTERISTICS
SPAN AND ZERO ACCURACY
VOLTAGE REFERENCE
ALARM CHARACTERISTICS
POWER REQUIREMENTS
(@ +258C, RL = 250 V and VS = +24 V, unless otherwise noted)
BUFFER AMPLIFIER
NOTES
1The single supply op amps of the AD694, lacking pull down current, may not reach 0.000 V at their outputs. For this reason, span, offset, and nonlinearity are
specified with the input amplifiers operating in their linear range. The input voltage used for the tests is 5 mV to 2 V and 5 mV to 10 V for the two precalibrated
input ranges. Span and zero accuracy are tested with the buffer amplifier configured as a follower.
2Offset at 4 mA out and 0 mA out are extrapolated to 0.000 V input from measurements made at 5 mV and at full scale. See Note 1.
3Nonlinearity is specified as the maximum deviation of the output, as a % of span, from a straight line drawn through the endpoints of the transfer function.
4Voltage reference drift guaranteed by the Box Method. The voltage reference output over temperature will fall inside of a box whose length is determined by the
temperature range and whose height is determined by the maximum temperature coefficient multiplied by the temperature span in degrees C.
5Devices tested at these temperatures with a pass transistor. Allowable temperature range of operation is dependent upon internal power dissipation. Absolute
maximum junction and case temperature should not be exceeded. See section: “Power Dissipation Considerations.”
6Buffer amplifier specs for reference. Buffer amplifier offset and drift already included in Span and Zero accuracy specs above.
Specifications subject to change without notice.
PIN CONFIGURATION (N, R, Q PACKAGE)
AD694
ABSOLUTE MAXIMUM RATINGSSupply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .+36 V
VS to IOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .+36 V
Input Voltage, (Either Input Pin 2 or 3) . . . . .–0.3 V to +36 V
Reference Short Circuit to Common . . . . . . . . . . . .Indefinite
Alarm Voltage, Pin 10 . . . . . . . . . . . . . . . . . . . . . . . . . .+36 V
4 mA Adj, Pin 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .+1 V
4 mA On/Off, Pin 9 . . . . . . . . . . . . . . . . . . . . . . . .0 V to 36 V
Storage Temperature Range
AD694Q . . . . . . . . . . . . . . . . . . . . . . . . .–65°C to +150°C
AD694N, R . . . . . . . . . . . . . . . . . . . . . . .–65°C to +125°C
Lead Temperature, 10 sec Soldering . . . . . . . . . . . . . .+300°C
Maximum Junction Temperature . . . . . . . . . . . . . . . . .+150°C
Maximum Case Temperature
Plastic Package (N, R) . . . . . . . . . . . . . . . . . . . . . . .+125°C
Cerdip Package (Q) . . . . . . . . . . . . . . . . . . . . . . . . .+125°C
No pin, other than IOUT (11) and ±Sig (2), (3) as noted, may be permitted to become more negative than Com (5). No pin may be
permitted to become more positive than VS (13).
ORDERING GUIDETransistor Count: . . . . . . . . . . . . . . . . . . . . .75 Active Devices
Substrate Connection: . . . . . . . . . . . . . . . . . . . .to Com, Pin 5
Thermal Characteristics:Plastic (N) Package:θJC = 50°C/Watt
θCA (Still Air) = 85°C/Watt
Cerdip (Q) Package:θJC = 30°C/Watt
θCA (Still Air) = 70°C/Watt
Plastic (R) Package:θJC = 27°C/Watt
θCA (Still Air) = 73°C/Watt
ESD SusceptibilityAll pins are rated for a minimum of 4000 V protection, except
for Pins 2, 3 and 9 which are rated to survive a minimum of
1500 V. ESD testing conforms to Human Body Model. Always
practice ESD prevention.
AD694Typical Minimum Supply Voltage vs. Temperature for 2 V
& 10 V Full Scale
Maximum RL vs. Supply Voltage
Voltage Reference Power Supply Rejection
FUNCTIONAL DESCRIPTIONThe operation of the AD694 can best be understood by dividing
the circuit into three functional parts (see Figure 1). First, a
single supply input amplifier buffers the high level, single-ended
input signal. The buffer amplifier drives the second section, a
voltage to current (V/I) converter, that makes a 0 to 16 mA sig-
nal dependent current.
Figure 1. Functional Block Diagram
The third section, a voltage reference and offset generator, is re-
sponsible for providing the 4 mA offset current signal.
BUFFER AMPLIFIERThe buffer amplifier is a single supply amplifier that may be
used as a unity gain buffer, an output amplifier for a current
output D/A converter, or as a gain block to amplify low level
signals. The amplifier’s PNP input stage has a common-mode
range that extends from a few hundred mV below ground to
within 2.5 V of VS. The Class A output of the amplifier appears
at Pin 1 (FB). The output range extends from about 1 mV
above common to within 2.5 V of VS when the amplifier is oper-
ated as a follower. The amplifier can source a maximum load of
5 kΩ, but can sink only as much as its internal 10 kΩ pulldown
resistor allows.
V/I CONVERTERThe ground referenced, input signal from the buffer amplifier is
converted to a 0 to 0.8 mA current by A2 and level shifted to
the positive supply. A current mirror then multiplies this signal
by a factor of 20 to make the signal current of 0 to 16 mA. This
technique allows the output stage to drive a load to within 2 V
of the positive supply (VS). Amplifier A2 forces the voltage at
Pin 1 across resistors R1 and R2 by driving the Darlington tran-
sistor, Q2. The high gain Darlington transmits the resistor cur-
rent to its collector and to R3 (900 Ω). A3 forces the level
shifted signal across the 45 Ω resistor to get a current gain of 20.
The transfer function of the V/I stage is therefore: OUT=20×VPIN1()/R1+R2()
resulting in a 0-16 mA output swing for a 0–10 V input. Tying
Pin 4 (2 V FS) to ground shorts out R2 and results in a 2 V
Table I. Precalibrated Ranges for the AD6940–2 V
0–10 V
0–2.5 V
0–12.5 V
0–2 V
0–10 V
0–2.5 V
BASIC CONNECTIONS: 12.5 V SINGLE SUPPLY
OPERATION WITH 10 V FSFigure 2 shows the minimal connections required for basic op-
eration with a +12.5 V power supply, 10 V input span, 4-20 mA
output span, and a 10 V voltage reference. The buffer amplifier
is connected as a voltage follower to drive the V/I converter by
connecting FB (Pin 1) to –Sig (Pin 2). 4 mA On/Off (Pin 9) is
tied to ground (Pin 5) to enable the 4 mA offset current. The
AD694 can drive a maximum load RL = [VS – 2 V] /20 mA,
thus the maximum load with a 12.5 V supply is 525 Ω.
SELECTING A 2 V FULL-SCALE INPUTThe 2 V full-scale option is selected by shorting Pin 4 (2 V FS)
to Pin 5 (Common). The connection should be as short as pos-
sible; any parasitic resistance will affect the precalibrated span
accuracy.
SELECTING THE 2 V VOLTAGE REFERENCEThe voltage reference is set to a 2 V output by shorting Pin 7 to
Pin 8 (10 V Force to 2 V Sense). If desired, the 2 V reference
can be set up for remote force and sense connection. Keep in
mind that the 2 V Sense line carries a constant current of 100 μA
that could cause an offset error over long wire runs. The 2 V
reference option can be used with all supply voltages greater
than 4.5 V.
drive a load to a point 36 V below the positive supply (VS). An
optional NPN pass transistor can be added to transfer most of
the power dissipation off-chip, to extend the temperature range
of operation.
The output stage is current-limited at approximately 38 mA to
protect the output from an overdrive at its inputs. The V/I will
allow linear operation to approximately 24 mA. The V/I con-
verter also has an open collector alarm (Pin 10) which warns of
open-circuit condition at the IOUT pin or of attempts to drive the
output to a voltage greater than VS –2 V.
4 mA OFFSET GENERATORThis circuit converts a constant voltage from the voltage refer-
ence to a constant current of approximately 200 μA. This cur-
rent is summed with the signal current at Pin 14 (BW Adjust),
to result in a constant 4 mA offset current at IOUT. The 4 mA
Adj (Pin 6) allows the offset current to be adjusted to any cur-
rent in the range of 2 mA to 4.8 mA. Pin 9 (4 mA On/Off) can
shut off the offset current completely if it is lifted to 3.0 V or
more, allowing 0 to 20 mA operation of the AD694. In normal
4-20 mA operation, Pin 9 is connected to ground.
VOLTAGE REFERENCEA 2 V or 10 V voltage reference is available for user applications,
selectable by pin-strapping. The 10 V option is available for
supply voltages greater than 12.5 V, the 2 V output is available
over the whole 4.5 V – 36 V power supply range. The reference
can source up to 5 mA for user applications. A boost transistor
can be added to increase the current drive capability of the 2 V
mode.
APPLYING THE AD694The AD694 can easily be connected for either dual or single
supply operation, to operate from supplies as low as 4.5 V and
as high as 36 V. The following sections describe the different
connection configurations, as well as adjustment methods.
Table I shows possible connection options.
AD694An NPN boost transistor can be added in the 2 V mode to in-
crease the current drive capability of the 2 V reference. The
10 V force pin is connected to the base of the NPN, and the
NPN emitter is connected to the 2 V sense pin. The minimum
VS Of the part increases by approximately 0.7 V.
4.5 V SINGLE SUPPLY OPERATIONFor operation with a +4.5 V power supply, the input span and
the voltage reference output must be reduced to give the ampli-
fiers their required 2.5 V of head room for operation. This is
done by adjusting the AD694 for 2 V full-scale input, and a
voltage reference output of 2 V as described above.
GENERAL DESIGN GUIDELINESA 0.1 μF decoupling capacitor is recommended in all applica-
tions from VS (Pin 13) to Com (Pin 5). Additional components
may be required if the output load is nonresistive, see section on
driving nonresistive loads. The buffer amplifier PNP inputs
should not be brought more than –0.3 V of common, or they
will begin to source large amounts of current. Input protection
resistors must be added to the inputs if there is a danger of this
occurring. The output of the buffer amplifier, Pin 1 (FB), is not
short circuit protected. Shorting this pin to ground or VS with a
signal present on the amplifier may damage it. Input signals
should not drive Pin 1 (FB) directly; always use the buffer am-
plifier to buffer input signals.
DRIVING NONRESISTIVE LOADSThe AD694 is designed to be stable when driving resistive loads.
Adding a 0.01 μF capacitor from IOUT (Pin 11) to Com (Pin 5),
as shown in Figure 3, insures the stability of the AD694 when
driving inductive or poorly defined loads. This capacitor is rec-
ommended when there is any uncertainty as to the characteris-
tics of the load.
Figure 3. Capacitor Utilized When Driving Nonresistive
Loads; Protection Diodes Used When Driving Inductive
Loads
Additional protection is recommended when driving inductive
loads. Figure 3 shows two protective diodes, D1 and D2, added
to protect against voltage spikes that may extend above VS or
below common that could damage the AD694. These diodes
should be used in addition to the 0.01 μF capacitor. When the
optional NPN transistor is used, the capacitor and diodes
should connect to the NPN emitter instead of Pin 11.
0-20 mA OPERATIONA 0-20 mA output range is available with the AD694 by remov-
ing the 4 mA offset current with the 4 mA On/Off pin. In nor-
mal 4-20 mA operation 4 mA On/Off (Pin 9) is tied to ground,
enabling the 4 mA offset current. Tying Pin 9 to a potential of
3 V or greater turns off the 4 mA offset current; connecting Pin
9 to the 10 V reference, the positive supply, or a TTL control
pin, is a convenient way to do this. In 0–20 mA mode the input
span is increased by 20%, thus the precalibrated input spans of
2 V and 10 V become 2.5 V and 12.5 V. Minimum supply volt-
ages for the two spans increase to 5 V and 15 V.
The 4 mA On/Off pin may also be used as a “jiggle pin” to
unstick valves or actuators, or as a way to shut off a 4–20 mA
loop entirely. Note that the pin only removes the 4 mA offset
and not the signal current.
DUAL SUPPLY OPERATIONFigure 4 shows the AD694 operated in dual supply mode. (Note
that the pass transistor is shown for illustration and is not re-
quired for dual supply operation.) The device is powered com-
pletely by the positive supply which may be as low as 4.5 V. The
unique design of the output stage allows the IOUT pin to extend
below common to a negative supply. The output stage can
source a current to a point 36 V below the positive supply. For
example, when operated with a +12.5 V supply, the AD694 can
source a current to a point as low as 23.5 V below common.
This feature can simplify the interface to dual supply D/A con-
verters by eliminating grounding and level-shifting problems
while increasing the load that the transmitter is able to drive.
Note that the IOUT pin is the only pin that should be allowed to
extend lower than –0.3 V of common.
OPERATION WITH A PASS TRANSISTORThe AD694 can operate as a stand-alone 4–20 mA converter
with no additional active components. However, provisions have
been made to connect IOUT to the base of an external NPN pass
transistor as shown in Figure 4. This permits a majority of the
power dissipation to be moved off-chip to enhance performance
and extend the temperature range of operation. Note that the
positive output voltage compliance is reduced by approximately
0.7 V, the VBE of the pass device. A 50 Ω resistor should be
added in series with the pass transistor collector, when the
AD694 is operated with dual supplies, as shown in Figure 4.
This will not reduce the voltage compliance of the output stage.
The external pass transistor selected should have a BVCEO
greater than the intended supply voltage with a sufficient power
rating for continuous operation with 25 mA current at the sup-
ply voltage. Ft should be in the 10 MHz to 100 MHz range and
β should be greater than 10 at a 20 mA emitter current. Heat
sinking the external pass transistor is suggested.
