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ISC300
Universal Precision Isolated MEASUREMENT CHANNEL
FEATURES
q CALIBRATION CAPABILITY q q q q q q INTEGRAL SENSOR EXCITATION OPEN CIRCUIT SENSOR DETECTION LOW POWER: 80mW INSTRUMENT AMPLIFIER INPUT PROGRAMMABLE GAIN 12-BIT LINEARITY
APPLICATIONS
q UNIVERSAL INPUT CHANNEL FOR PROCESS CONTROL SYSTEMS q ISOLATED MEASUREMENT CHANNEL FOR THERMOCOUPLE, RTD AND VOLTAGE TRANSDUCERS q CHANNEL TO CHANNEL ISOLATED MULTIPLEXED SYSTEMS q ISOLATED 4 TO 20mA RECEIVER
q TWO ISOLATED POWER SUPPLIES: 13V at 5mA q LOW DRIFT 10V REFERENCE
DESCRIPTION
The ISC300 is an isolated measurement channel with open circuit sensor detection for use with RTD and thermocouple temperature sensors. In addition to temperature measurement, the ISC300 can accept full scale input voltages of 100mV and 10V which allows use with other sensors such as pressure, humidity and flow sensors. The low level resistance measurement capability also allows stimulus and measure9 2 +VISO -VISO 20M 8 Sense 2 5 6 +IP Filter -IP 20M 3 Sense 1 -VISO Ref 1 4 7 10 VREF IREF1 IREF2 Com 1 99R 0.100V Current Reference -VISO R Com 1 Channel 4 A0 A1 O P T O Channel 3 Com 1 Com 2 VDD (+5) CLK C O U P L E L A T C H 18 22 10.0V MUX Channel 2 VCC (+15) 25 Rectify Power CKI Com 2 26 27 Channel 1 Out PGA Modulate Demod +VISO Out 28 Barrier
ment of strain gauges. The measurement channel has a highly stable internal reference which can be selected from the output side. This allows the user to calibrate each channel at the factory, record the calibration data and periodically recalibrate the system while in use over time and ambient temperature changes.
INPUT SELECT Com1 +0.1V +10V Signal GAIN SELECT 0.5 50 SELECT and GAIN No Change No Change Latch RESET
A1 0 0 1 1
A0 0 1 0 1
G 0 1
G A0 A1 RST
19 20 21
RST 1 1 1 0
CLK 0 1 ^ X
23 24
Input Side
Output Side
DCom 2
International Airport Industrial Park * Mailing Address: PO Box 11400 Tel: (520) 746-1111 * Twx: 910-952-1111 * Cable: BBRCORP *
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* Tucson, AZ 85734 * Street Address: 6730 S. Tucson Blvd. * Tucson, AZ 85706 Telex: 066-6491 * FAX: (520) 889-1510 * Immediate Product Info: (800) 548-6132 PDS-1135A Printed in U.S.A. October, 1993
1991 Burr-Brown Corporation
SPECIFICATIONS
ELECTRICAL
At VCC = 15V, VDD = 5V, TA = +25C, unless otherwise noted. ISC300 PARAMETER ISOLATION Isolation Voltage (VISO) CONDITIONS AC60Hz Continuous AC60Hz Continuous VISO, DC Partial Discharge(1) VISO = Rated 60Hz Cont(2) VISO = 240 Vrms 60Hz 50, 0.5 10 0C to +70C VO = -5V to +5V(4) VIN = 0V G = 0.5 VIN = 0V G = 50 0C to +70C G = 0.5 0C to +70C G = 50 VCC = 14V to 16V 30 0.01 3 50 0.025 200 5 200 5 MIN 500 700 700 800 110 2 || 15 4 TYP MAX UNITS Vrms VPEAK V Vrms dB G || pF Arms V/V mV/ % ppm/C % mV mV V/C V/C mV/V nA pA/C V V V M dB dB dB k V V k mVrms mVp-p Hz s s ms ms V % ppm/C ppm/kHr %/V mV % ppm/C ppm/kHr %/V V mA V mA mW V mA
Isolation Mode Rejection (IMR) Barrier Impedance Leakage Current (IISO) GAIN Voltage Gains Resistance Conversion Initial Error vs Temperature Nonlinearity INPUT OFFSET VOLTAGE Initial Offset (Input Referred) vs Temperature vs Supply (VCC) INPUT CURRENT Initial Bias vs Temperature INPUT Voltage Range Resistance Range Peak Voltage Impedance: Differential Common Mode Rejection
1.5 35 100
50
-40C to +85C Rated Operation G = 0.5V Input Rated Operation G = 50V Input Rated Operation G = 50 3-wire Resistance Applied to Any Signal Input Wrt Com 1(5) CMR at DC Gain = 0.5(3) CMR at DC Gain = 50(3) CMR at 60Hz(3) For Normal Operation < 1k Imbalance Min Load = 1M During Input Fault (VIN < -11V or VIN > 11V) f = 0 to 5kHz Min Load 1M f = 0 to 100kHz Min Load 1M
0 10 66 75 60
10 0.1 500 380 75 100 70 10 5 3 0.5 10 3.5 0.5 5 1 2 10 0.1 10
Source Impedance Imbalance OUTPUT Voltage Range Overrange Voltage Output Impedance Ripple Voltage FREQUENCY RESPONSE Input Bandwidth Input Settling Time Input Overload Recovery Output Overload Settling Time Output Overload Recovery VOLTAGE REFERENCE VREF1 (Internal and External) Initial Accuracy vs Temperature vs Time vs Supply (VCC) VREF2 (Internal) Initial Accuracy(6) vs Temperature vs Time vs Supply (VCC) POWER SUPPLIES Analog Supply Range Supply Current Digital Supply Range Supply Current Total Power Dissipation Isolated Supplies: Voltage Current
5.4
TSETT, to within 5% for VIN < 14V
5
External Loading of 100nA
1 20 20
100 0.1 10
1 20 20
VCC Pin No External Load VDD Pin No External Load at 5mA Each Supply
14 5 4 1 80 13 5
16 10 6 3 184
11.5
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ISC300
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SPECIFICATIONS
ELECTRICAL
(CONT)
At VCC = 15V, VDD = 5V, TA = +25C, unless otherwise noted. ISC300 PARAMETER INPUT O/C SENSE Sense Current REFERENCE CURRENT Reference Current (IREF1) Reference Currents Ratio CONDITIONS IS2, Sense 1 = 0V -IS2, Sense 2 = 0V 199 IREF1 : IREF2 3.5 1.5 450 20 20 5 5 11 4 350 350 50 MIN TYP 0.7 0.7 200 201 0.5 MAX UNITS A A A % V V ns ns ns ns ns V V A A kHz % C C C C/W C
DIGITAL INPUTS A0, A1, G, CLK, RST (74HC EQUIVALENT) High-Level Input Voltage Low-Level Input Voltage Input Rise and Fall Times (tR, tr) CLK RST A0, A1, G Pulse Width (tW) CLK, RST Setup (tSU) Data Change to CLK High Hold (tHO) Data Change from CLK High Release (tREG) RST High to CLK High CLOCK SYNC CKI Input Voltage - High Level Input Voltage - Low Level Input Current - High Level Input Current - Low Level Input Frequency Input Duty Cycle TEMPERATURE RANGE Specification Operating Storage JA TJ max VCC = 15V VCC = 15V VIL = 11V VCC = 15V VIL = 4V VCC = 15V
45 45 0 0 -40
55 55 70 70 85
220 150
NOTES: (1) See "High Voltage Testing" Section. (2) IMR is defined with respect to the voltage between Com 1 and Com 2 with both inputs tied to Com 1. (3) CMR is defined with respect to the input common, Com 1, only. (4) Deviation from a straight line between the end points of the output voltage. (5) Device output remains monotonic. (6) Limit referred to VREF1.
PIN CONFIGURATION
Bottom View 1 2 3 4 5 6 7 8 9 10 10V Ref -VSS1 Sense 1 IREF1 +In -In IREF2 Sense 2 +VSS1 Com 1
ABSOLUTE MAXIMUM RATINGS
Signal Input Voltage ......................................................................... 380V Analog Supply Voltage VCC .................................................................. 18V Digital Supply Voltage VDD ..................................................................... 7V Voltage Across Barrier ................................................................. 800Vrms Storage Temperature Range .......................................... -45C to +100C Lead Temperature (soldering, 10s) ................................................ +300C Out Short Circuit Duration ........................................ Continuous to Com 2 Relative Humidity (non-condensing) ............................................. 95% RH NOTES: Stresses exceeding those listed above may cause permanent damage to the device. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
TIMING INFORMATION
18 19 20 21 22 23 24 25 26 27 28 VDD (+5V) G A0 A1 CLK RST DCom 2 VCC (+15V) CKI Com 2 Out tSU Data tHO CLK tW tW RST t REL tW
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ISC300
THEORY OF OPERATION
The ISC300 has no galvanic connection between the input and output sections. The differential input signal is multiplied by the programmable gain amplifier and accurately transferred across the isolation barrier to the output. The output section demodulates the signal transferred from the input section and transfers power to the input section. ISC300 DESIGN The ISC300 consists of: * A filtered differential high impedance input. * Precision matched current sources. * Fault detect bias resistors. * Digitally selectable internal calibration references. * Digitally selectable gain. * Isolation of all digital and analog signals. * Isolated DC/DC converter. * Synchronizable internal oscillator. * Two isolated power supplies available for external circuitry. * Externally available 10V reference. INPUT SECTION Filter Since the ISC300 is designed to measure slowly changing processes, the input filter is set for a cut off frequency of 2Hz. This gives good noise rejection at power frequencies of 50Hz and 60Hz.
Sense Lines The two sense lines can be configured to detect short or open circuits e.g. transducer burn out. This would be indicated by an out of range output (see Input Configuration in Applications section). Multiplexer The multiplexer is used to route either the measurement channel or the precision voltage references (used in system calibration) to the programmable gain amplifier. Isolation Barrier The isolation barrier consists of two transformers and three opto couplers. One transformer transmits the signal from the input side to the output side. The other transmits power from the output side to the input side. The opto-couplers are used to isolate the logic used for mux select, gain and reference voltage control. Voltage Reference The voltage reference provides 10V, 0.1V and 0V references for channel calibration. The 10V reference is also available externally. Current References Two matched 200A current references are available for the excitation of RTDs or for use in external signal conditioning circuitry.
9 2
+VISO -VISO 20M Barrier +VISO Out Filter Channel 1 Out PGA Modulate Demod 28
8 Sense 2 5 6 +IP -IP 20M 3 Sense 1
-VISO Ref 10.0V 99R 0.100V Current Reference -VISO R Com1
MUX Channel 2
VCC (+15) 25 Rectify Power CKI Com 2 26 27 18 22
1 4 7 10
VREF IREF1 IREF2 Com 1
Channel 3 Com 1 Channel 4 A0 A1 O P T O Com 2 VDD (+5) CLK C O U P L E L A T C H
G A0 A1 RST
19 20 21
23 24
Input Side
Output Side
DCom 2
FIGURE 1. ISC300 Block Diagram.
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ISC300
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PGA The programmable gain amplifier allows the user to digitally select device gains of 0.5 and 50, allowing input ranges of 0.1V or, 10V full scale. When used in conjunction with the 0.1V, 10V and common references, channel calibration can be performed. Isolated Supplies Two 13V isolated supplies, capable of supplying 5mA each, are available to power signal conditioning circuitry. OUTPUT SECTION The output section passes power across the isolation barrier to provide the isolated supplies, and demodulates the signal transmitted back across the isolation barrier. ABOUT THE BARRIER For any isolation product, barrier integrity is of paramount importance in achieving high reliability. The ISC300 uses miniature transformers designed to give maximum isolation performance when encapsulated in a high dielectric strength material. The device is designed so that the barrier is located at the center of the package. HIGH VOLTAGE TESTING Burr-Brown Corporation has adopted a partial discharge test criterion that conforms to the German VDE0884 Optocoupler Standards. This method requires the measurement of minute current pulses (< 5pC) while applying 800Vrms, 60Hz high-voltage stress across every device isolation barrier. During a two second test partial discharge must occur five times on five separate half cycles of 60Hz, and each time occurrence must not be separated by a line period of more than four half cycles in order to produce a partial discharge fail. This confirms transient overvoltage (1.6 x Vrated) protection without damage. Life-test results verify the absence of failure under continuous rated voltage and maximum temperature. This new test method represents the "state-of-the-art" for nondestructive high voltage reliability testing. It is based on the effects of non-uniform fields existing in heterogeneous dielectric material during barrier degradation. In the case of void non-uniformities, electric field stress begins to ionize the void region before bridging the entire high voltage barrier. The transient conduction of charge during and after the ionization can be detected externally as a burst of 0.01s - 0.1s current pulses that repeat on each AC voltage cycle. The minimum AC barrier voltage that initiates partial discharge is defined as the "inception voltage." Decreasing the barrier voltage to a lower level is required before partial discharge ceases and is defined as the "extinction voltage." We have designed and characterized the package to yield an inception voltage in excess of 800Vrms so that transient
overvoltages below this level will not cause any damage. The extinction voltage is above 500Vrms so that even overvoltage-induced partial discharge will cease once the barrier voltage is reduced to the rated level. Older high voltage test methods relied on applying a large enough overvoltage (above rating) to catastrophically break down marginal parts, but not so high as to damage good ones. Our new partial discharge testing gives us more confidence in barrier reliability than breakdown/no breakdown criteria.
BASIC OPERATION
SIGNAL AND SUPPLY CONNECTIONS As with any mixed signal analog and digital signal component, correct decoupling and signal routing precautions must be observed to optimize performance. The ISC300 has an internal 0.1F decoupling capacitor at VCC, so additional VCC decoupling will not be necessary. However, a ground plane will minimize potential noise problems. If a low impedance ground plane is not used, Com 2 should be tied directly to the ground at the supply. It is not necessary to connect DCom 2 and Com 2 at the device. Layout practices associated with isolation signal conditioners are very important. The capacitance associated with the barrier and series resistance in the signal and reference leads must be minimized. Any capacitance across the barrier will increase AC leakage, and in conjunction with ground line resistance, may degrade high frequency IMR, see Figure 2. INPUT CONFIGURATION The ISC300 allows easy configuration for temperature measurement using an RTD. Figure 3 shows the basic connections for RTD operation. The two reference currents excite the resistance transducer and a current-to-voltage conversion is made corresponding to the resistance value of the transducer. If a gain of 50 is selected, a 10 resistance value results in a (10 * 200A) * 50 = 0.1V output; the 500 full scale value gives a (500 * 200A) * 50 = 5V output. The connection of the sense line allows open circuit sensor detection. An open circuit will give a corresponding > 5.1V output. A short circuit will give a corresponding < 0.1V output. See the Applications section under Fault Conditions for more information.
CINT Com 2 CEXT Com 1 VISO R
FIGURE 2. Barrier Capacitance.
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ISC300
Figure 4 shows the configuration for voltage measurement. A full scale input range of 10V can be accepted by the ISC300. The two sense lines can be connected to give open or short circuit detection. An open circuit will result in an output of < -5.1V and a short circuit will give a < 0.1V output. See the Applications section under Fault Conditions for more information. Figure 7 shows a possible circuit configuration using jumpers to select voltage or RTD operation.
ISOLATED SUPPLIES The two isolated supplies available on the input side are capable of supplying 11.5V min at 5mA. These can be used to provide power for external front-end circuitry for additional signal processing. When using the isolated supplies, it is necessary to decouple them as close to the device as possible. 10F tantalum capacitors should be used. This will also improve the signal-to-noise ratio.
Line Resistance
Com 1 +In
Com 1
0 to 500
RS
- In
Filter and MUX
PGA
Sense 2 20M IREF1 IREF2
+VISO
I1
I2 -VISO
FIGURE 3. Resistance Measurement Configuration.
Sense 1 20M Line Resistance -10V to +10V +In -In Filter and MUX
-VISO
PGA
Sense 2 20M
+VISO
Com 1
FIGURE 4. Voltage Measurement Configuration.
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ISC300
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MEASUREMENT CHANNEL CALIBRATION The ISC300 is designed to allow easy system calibration using its internal voltage reference. Programming pins A0, A1 and G allows offset and full scale errors in gains of 0.5 and 50 to be measured.
INPUT SELECT Com 1 +0.1V +10V Signal GAIN SELECT 0.5 50 SELECT AND GAIN No Change No Change Latch RESET
pins of each ISC300 in the system together (see Figure 6). The ISC300 can also be synchronized by an external clock driver.
Optional Clock Driver
A1 0 0 1 1
A0 0 1 0 1
G 0 1
RST 1 1 1 0
CLK 0 1 ^ X
CKI
CKI
CKI
CKI
CKI
CKI
ISC300
ISC300
ISC300
ISC300
ISC300
FIGURE 6. Synchronizing Multi-ISC300 Applications. System calibration would typically proceed as follows: Lab Calibration * Set ISC300 gain. * Set input to 0V reference, measure Offset. * Connect external precision V reference, measure Gain. * Remove external V reference and set input to 10V or 0.1V reference. Offset and Gain are now calibrated to an external precision reference--record the numbers. Field Calibration * Set ISC300 gain. * Set input to 0V reference, measure Offset. * Set input to 10V or 0.1V, measure Gain. * Recalibrate system. SYNCHRONIZATION As the internal modulation frequencies of several ISC300s can be marginally different, `beat' frequencies ranging from a few Hz to a few kHz can exist in multi ISC300 applications. The internal clock (see Figure 5) starts when power is applied and runs at typically 50kHz. The ISC300 design accommodates `internal synchronous' noise which is caused by minute timing differences, but synchronous beat frequency noise will not be strongly attenuated, especially at low frequencies if it is introduced via the power, signal or ground paths. To overcome this problem, the design allows the synchronization of each oscillator in the system to one frequency. This is done by connecting the CKI (clock in) NOISE Output noise is generated by the residual components of the 25kHz carrier that have not been removed from the signal. This noise may be reduced by adding an output low pass filter (see Figure 15 for an example of a 2 pole filter with amplification, giving a 10V output). The filter time constants should be set below the carrier frequency. The output of the ISC300 is a switched capacitor and requires a high impedance load to prevent degradation of linearity. Loads of less than 1M will cause an increase in noise at the carrier frequency and will appear as ripple in the output waveform.
APPLICATIONS
This section describes the design criteria of various applications of the ISC300. 2, 3 AND 4 WIRE RESISTANCE MEASUREMENTS Two wire resistance measurements are prone to errors due to lead resistances. The voltage error can be significant since the voltmeter measures on the lines supplying the RTD
20M -VISO -VISO
Sense 1 2 J1 +In -In 1 J2 2 Sense 2 3 1 3 +In -In IREF2 IREF1
Filter and MUX
PGA
-VISO +VISO 20M Com 1
220pF
Com Com 1
CKI
39k
Jumper Mode Voltage RTD
J1 1-2 2-3
J2 1-2 2-3
f = 50kHz
Simplified Schematic
FIGURE 5. CKI Input.
FIGURE 7. Mode Selection Jumpers.
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ISC300
ISC300
N
1
2
3
4
5
excitation current. Four wire measurements avoid this problem by measuring the voltage generated across the RTD on a second pair of wires. Very little current flows through the voltmeter, therefore the lead resistance error contribution is negligible. Three wire resistance measurements also avoid lead length resistance errors. In Figure 8: (+In) = -r1 (I1 + I2) - r2I1 (-In) = -r1 (I1 + I2) - R2I2 - r3I2 (1) - (2) = -r2I2 + RSI2 + r3I2 Since r1 = r2 = r3
(LEADS)
Com 1
+In RS 0V -In
(1) (2)
I1
I2
and I1 = I2
Output < +0.1V
-VISO
VIN = RS I2 FIGURE 10. RS Short Circuit. FAULT CONDITIONS The ISC300 can be configured to detect line or transducer faults which may occur in a system. Figures 8 to 14 show how the output of the ISC300 will reflect these various fault conditions by giving corresponding out of range outputs.
RS -VISO -In I1 I2 Com 1
+In
T1 Com 1 I 1 + I2
T2 +In
RS
T3
I2 * RS = VIN -In I1 I2
Output < -5.1V
-VISO
FIGURE 11. +In Open Circuit.
Com 1
Output = G * VIN
-VISO
+In RS Com 1 I1 +In I2 +VISO -In
FIGURE 8. Normal Operation.
RS
+VISO -In I1 I2
Output > +5.1V
-VISO
FIGURE 12. -In Open Circuit.
Output > +5.1V
-VISO
FIGURE 9. RS Open Circuit.
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ISC300
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Com 1
Com 1
+In RS Undefined -In I1 I2
+In RS Undefined -In I1 I2
Output Undefined
-VISO
Output Undefined
-VISO
FIGURE 13. -In and +In Open Circuit.
FIGURE 14. Com 1 Open Circuit. excite the measurement bridge and the INA102 is used to amplify the bridge delta voltage. Connecting pins 4 and 7 together, and pins 5 and 6 together on the INA102 sets its gain to 1000. ISOLATED 4 TO 20MA RECEIVER In Figure 17, the ISC300 converts a 4 to 20mA current to an isolated 0 to 5V output. The 6.25 resistor converts the 4 to 20mA input to 0.025 to 0.125V. The 125 resistor in conjunction with the 200A current source provides an offset of -0.025V. Fine offset and gain adjustment gives an accurate 0 to 0.1V input range. Offset and Gain Adjustment * Adjust R1 for 5V change on the output corresponding to 16mA change on the input. * Adjust R2 with 4mA input for 0V output.
APPLICATIONS FLEXIBILITY
ISOLATED VOLTAGE MEASUREMENT CHANNEL Figure 15 shows the ISC300 configured for a 10V input. With a few external components the ISC300 can accurately convert a 10V input to an isolated 10V output with no external adjustments. The primary function of the output circuitry is to add gain to convert the 5V output of the ISC300 to 10V, and to reduce output impedance. The addition of a few resistors and capacitors provides an active low pass filter with a cut off frequency of typically 200Hz. The filter response is flat to 1dB and rolls off from cut off at -12dB per octave. ISOLATED MEASUREMENT BRIDGE CIRCUIT Figure 16 shows a measurement bridge circuit using the ISC300. All the input circuitry is powered by the ISC300 isolated supplies. The OPA1013 dual op amp is used to
+VCC Sense 1 100k +In Out 6.8nF ACom 2 +10VIN 100k
6.8nF
OPA27GP
10VOUT
22k
-In Sense 2 Com 1 DCom 2 Logic Control
+VDD
22k
-3dB = 200Hz
FIGURE 15. Isolated Voltage Measurement Channel with Output Filter.
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ISC300
1/2 OPA1013 +VSS1 +VSS1 -VSS1 20k VREF1
B
+VCC
Out ACom 2
10k +VSS1 +In
INA102
-VSS1
+VDD
-In 1k 100k 1k -VSS1 Com 1 DCom 2 Logic Control
1k 100k +VSS1
1k
A
-VSS1 1/2 OPA1013
FIGURE 16. Isolated Instrument Bridge System.
+VCC
R1 125 20 4 to 20mA 6.25 10 330 10 100 220 R2
+In
Out ACom 2
0 to 5V
-In IREF1
+VDD
+VDD Com 1 DCom 2
FIGURE 17. Isolated 4 to 20mA receiver (0 to 5V output).
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ISC300
10
+VCC
+VSS1 -VSS1
IREF2
Out ACom 2
+VSS1 +In
INA102
+VDD
-In -VSS1 IREF1 Com 1 DCom 2 Logic Control
FIGURE 18. Temperature Measurement Using Thermocouple with Small Span.
+VCC
+VSS1 -VSS1
IREF2
Out ACom 2
+VSS1 +In
INA102
+VDD
-In -VSS1 IREF1 Com 1 DCom 2 Logic Control
4990 30
100
FIGURE 19. Thermocouple with Cold Junction Compensation.
The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes no responsibility for the use of this information, and all use of such information shall be entirely at the user's own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant any BURR-BROWN product for use in life support devices and/or systems.
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ISC300

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