AD694JNZ Analog Devices Inc, AD694JNZ Datasheet - Page 6

• Manufacturer Part Number: AD694JNZ
• Description: IC TRANSMITTER 4-20MA 16-DIP
• Manufacturer: Analog Devices Inc
• Type: Current Transmitterr

Specifications of AD694JNZ

• Input Type: Voltage
• Output Type: Voltage
• Current - Supply: 23mA
• Mounting Type: Through Hole
• Package / Case: 16-DIP (0.300", 7.62mm)
• Number Of Channels: 1
• Number Of Elements: 3
• Power Supply Requirement: Single
• Common Mode Rejection Ratio: 80dB
• Voltage Gain Db: 93.98dB
• Input Resistance: 5@24VMohm
• Input Offset Voltage: 0.5@24VmV
• Input Bias Current: 0.005@24V@-40C TO 85nA
• Single Supply Voltage (typ): 5/9/12/15/18/24/28V
• Dual Supply Voltage (typ): Not RequiredV
• Power Supply Rejection Ratio: 80dB
• Rail/rail I/o Type: No
• Single Supply Voltage (min): 4.5V
• Single Supply Voltage (max): 36V
• Dual Supply Voltage (min): Not RequiredV
• Dual Supply Voltage (max): Not RequiredV
• Operating Temp Range: 0C to 70C
• Operating Temperature Classification: Commercial
• Mounting: Through Hole
• Pin Count: 16
• Package Type: PDIP
• No. Of Amplifiers: 4
• Bandwidth: 300kHz
• Amplifier Output: Differential
• Cmrr: 90dB
• Supply Voltage Range: 4.5V To 36V, 12.5V To 36V
• Supply Current: 2mA
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Interface: -
• Lead Free Status / Rohs Status: RoHS Compliant part Electrostatic Device

AD694
An 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
V
4.5 V SINGLE SUPPLY OPERATION
For operation with a 4.5 V power supply, the input span and the
voltage reference output must be reduced to give the amplifiers
their required 2.5 V of headroom for operation. This is done by
adjusting the AD694 for 2 V full-scale input, and a voltage ref-
erence output of 2 V as described above.
GENERAL DESIGN GUIDELINES
A 0.1 µF decoupling capacitor is recommended in all applica-
tions from V
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 negative than –0.3 V from com-
mon, or they will begin to source large amounts of current. In-
put 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 V
it. Input signals should not drive Pin 1 (FB) directly; always use
the buffer amplifier to buffer input signals.
DRIVING NONRESISTIVE LOADS
The AD694 is designed to be stable when driving resistive loads.
Adding a 0.01 µF capacitor from I
as shown in Figure 3, ensures 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 V
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.
S
Of the part increases by approximately 0.7 V.
S
S
with a signal present on the amplifier may damage
(Pin 13) to Com (Pin 5). Additional components
OUT
(Pin 11) to Com (Pin 5),
S
or
–6–
0-20 mA OPERATION
A 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, the 4 mA On/Off (Pin 9) is tied to
ground, enabling the 4 mA offset current. Tying Pin 9 to a po-
tential of 3 V or greater turns off the 4 mA offset current; con-
necting 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 voltages 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 OPERATION
Figure 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 I
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 DACs by
eliminating grounding and level-shifting problems while increas-
ing the load that the transmitter is able to drive. Note that the
I
than –0.3 V of common.
OPERATION WITH A PASS TRANSISTOR
The AD694 can operate as a stand-alone 4–20 mA converter
with no additional active components. However, provisions have
been made to connect I
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 V
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 BV
greater than the intended supply voltage with a sufficient power
rating for continuous operation with 25 mA current at the sup-
ply voltage. F
β should be greater than 10 at a 20 mA emitter current. Heat
sinking the external pass transistor is suggested.
OUT
pin is the only pin that should be allowed to extend lower
BE
T
of the pass device. A 50 Ω resistor should be
should be in the 10 MHz to 100 MHz range and
OUT
to the base of an external NPN pass
OUT
pin to extend
CEO
REV. B