Analog Devices AD694JN, AD694BR, AD694BQ, AD694AR, AD694AQ Datasheet

a

4–20 mA Transmitter

	AD694*
FEATURES	FUNCTIONAL BLOCK DIAGRAM
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 DESCRIPTION

The 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 commonly 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 input 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 common 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 adjustments 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 transmission 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.

*Protected by U.S. Patents: 30,586; 4,250,445; 4,857,862.

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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.

PRODUCT HIGHLIGHTS

1.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 below 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.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: [phone] Fax: [phone]

AD694–SPECIFICATIONS (@ +258C, RL = 250 V and VS = +24 V, unless otherwise noted)

Model			AD694JN/AQ/AR			AD694BQ/BR
		Min	Typ	Max	Min	Typ	Max	Units
INPUT CHARACTERISTICS
Input Voltage Range		–0.2	VS–2.0 V	VS–2.5 V	–0.2	VS–2.0 V	VS–2.5 V	V
Input Bias Current
Either Input, TMIN to TMAX			1.5	5		1.5	5	nA
Offset Current, TMIN to TMAX			±0.1	61		±0.1	61	nA
Offset Current Drift			±1.0	±5.0		±1.0	±5.0	pA/°C
Input Impedance		5			5			MΩ
OUTPUT CHARACTERISTICS
Operating Current Range		0		23	0		23	mA
Specified Performance		4		20	4		20	mA
Output Voltage Compliance		VS–36 V		VS–2 V	VS–36 V		VS–2 V	V
Output Impedance, 4–20 mA		40.0	50.0		40.0	50.0		MΩ
Current Limit (@ 2 × FS Overdrive		24		44	24		44	mA
Slew Rate			1.3			1.3		mA/μs
SPAN AND ZERO ACCURACY1
4 mA Offset Error @ 0 V Input2			±10			±5		μA
Error from 4.000 mA, 4 mA On				620			610
Error from 0.000 mA, 4 mA Off		0	+10	+20	0	+5	+10	μA
TMIN to TMAX			±10	640		±5	620	μA
vs. Supply (2 V Span/10 V Span)			0.3/0.05	0.8/0.4		0.3/0.05	0.8/0.4	μA/V
Trim Range, 4 mA Zero		2.0		4.8	2.0		4.8	mA
Span
Nominal Transfer Function
Input FS = 2 V			8.0			8.0		mA/V
Input FS = 10 V			1.6			1.6		mA/V
Transfer Function Error from Nom,			±0.1			±0.05
Input FS = 2 V, 10 V				60.3			60.15	% of Span
TMIN to TMAX			±0.002	±0.005		±0.001	60.0025	% of Span/°C
vs. Supply			±0.001	60.005		±0.001	60.005	% of Span/V
Nonlinearity3			±0.005	60.015		±0.001	60.005	% of Span
4 mA On: Max Pin 9 Voltage				0.8			0.8	V
4 mA Off: Min Pin 9 Voltage		3.0	2.5		3.0	2.5		V
VOLTAGE REFERENCE
Output Voltage: 10 V Reference		9.960	10.000	10.040	9.980	10.000	10.020	V
Output Voltage: 2 V Reference		1.992	2.000	2.008	1.996	2.000	2.004	V
4			30	50		20	30	ppm/°C
TMIN to TMAX
vs. Load, VREF = 2 V, 10 V			0.15	0.50		0.15	0.50	mV/mA
vs. Supply, VREF = 2 V, 10 V			±0.001	60.005		±0.001	60.005	%/V
Output Current
Source		5			5			mA
Sink			0.2			0.2		mA
ALARM CHARACTERISTICS
VCE(SAT) @ 2.5 mA			0.35			0.35		V
Leakage Current				61			61	μA
Alarm Pin Current (Pin 10)			20			20		mA
POWER REQUIREMENTS
Specified Performance			24			24		V
Operating Range
2 V FS, VREF = 2 V		4.5		36	4.5		36	V
2 V, 10 V FS, VREF = 2 V, 10 V		12.5		36	12.5		36	V
Quiescent Current, 4 mA Off			1.5	2.0		1.5	2.0	mA
TEMPERATURE RANGE								°C
Specified Performance5	AD694AQ/BQ/AR/BR	–40		+85	–40		+85
	AD694JN	0		+70	0		+70	°C
Operating	AD694AQ/BQ/AR/BR	–55		+125	–55		+125	°C
	AD694JN	–40		+85	–40		+85	°C

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							AD694
Model	AD694JN/AQ/AR			AD694BQ/BR
	Min	Typ	Max	Min	Typ	Max	Units
BUFFER AMPLIFIER6
Input Offset Voltage		± 150			± 50		mV
Initial Offset			6500			6500
TMIN to TMAX		± 2	± 3		± 2	± 3	mV/°C
vs. Supply	80	90		80	90		dB
vs. Common Mode	80	90		80	90		dB
Trim Range	62.5	± 4.0		62.5	± 4.0		mV
Frequency Response
Unity Gain, Small Signal		300			300		kHz
Input Voluge Noise (0.1 Hz to 10 Hz)		2			2		mV p-p
Open-Loop Gain
VO = +10 V, RL ³ 10 kW		50			50		V/mV
Output Voltage @ Pin 1, FB1
Minimum Output Voltage		1.0	10		1.0	10	mV
Maximum Output Voltage	VS–2.5 V	VS–2 V		VS–2.5 V	VS–2 V		V

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.

ABSOLUTE MAXIMUM RATINGS
Supply 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	–65°C to +150°C
AD694Q . . . . . . . . . . . . . . . . . . . . . . .
AD694N, R . . . . . . . . . . . . . . . . . . . . .	. . –65°C to +125°C
Lead Temperature, 10 sec Soldering . . . .	. . . . . . . . . . +300°C
Maximum Junction Temperature . . . . . . .	. . . . . . . . . . +150°C
Maximum Case Temperature	+125°C
Plastic Package (N, R) . . . . . . . . . . . . .
Cerdip Package (Q) . . . . . . . . . . . . . . .	. . . . . . . . . . +125°C

Transistor Count: . . . . . . . . . . . . . . . . . . . . .75 Active Devices Substrate Connection: . . . . . . . . . . . . . . . . . . . . to Com, Pin 5

Thermal Characteristics:

Plastic (N) Package: qJC = 50°C/Watt

qCA (Still Air) = 85°C/Watt Cerdip (Q) Package: qJC = 30°C/Watt

qCA (Still Air) = 70°C/Watt Plastic (R) Package: qJC = 27°C/Watt

qCA (Still Air) = 73°C/Watt

ESD Susceptibility

All 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.

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).

PIN CONFIGURATION (N, R, Q PACKAGE)		ORDERING GUIDE
		Temperature	Package
	Model	Range	Option*
	AD694JN	0°C to +70°C	N-16
	AD694AQ	–40°C to +85°C	Q-16
	AD694AR	–40°C to +85°C	R-16
	AD694BQ	–40°C to +85°C	Q-16
	AD694BR	–40°C to +85°C	R-16

*N = Plastic DIP; Q = Cerdip, R = SOIC.

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AD694

FUNCTIONAL DESCRIPTION

The 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 signal dependent current.

Typical Minimum Supply Voltage vs. Temperature for 2 V & 10 V Full Scale

Maximum RL vs. Supply Voltage

Voltage Reference Power Supply Rejection

IOUT: Voltage Compliance vs. Temperature

Figure 1. Functional Block Diagram

The third section, a voltage reference and offset generator, is responsible for providing the 4 mA offset current signal.

BUFFER AMPLIFIER

The 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 operated as a follower. The amplifier can source a maximum load of 5 kW, but can sink only as much as its internal 10 kW pulldown resistor allows.

V/I CONVERTER

The 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 transistor, Q2. The high gain Darlington transmits the resistor current to its collector and to R3 (900 W). A3 forces the level shifted signal across the 45 W resistor to get a current gain of 20. The transfer function of the V/I stage is therefore:

I = æ		20 ´ V	(	ö	/ (R1 + R2)
OUT	è			)ø
				PIN1

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 full-scale input for a 16 mA output span.

The output stage of the V/I converter is of a unique design that allows the IOUT pin to drive a load below the common (substrate) potential of the device. The output transistor can always

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