® ISC300 Universal Precision Isolated MEASUREMENT CHANNEL FEATURES APPLICATIONS ● CALIBRATION CAPABILITY ● UNIVERSAL INPUT CHANNEL FOR PROCESS CONTROL SYSTEMS ● ISOLATED MEASUREMENT CHANNEL FOR THERMOCOUPLE, RTD AND VOLTAGE TRANSDUCERS ● CHANNEL TO CHANNEL ISOLATED MULTIPLEXED SYSTEMS ● ISOLATED 4 TO 20mA RECEIVER ● ● ● ● ● ● INTEGRAL SENSOR EXCITATION OPEN CIRCUIT SENSOR DETECTION LOW POWER: 80mW INSTRUMENT AMPLIFIER INPUT PROGRAMMABLE GAIN 12-BIT LINEARITY ● TWO ISOLATED POWER SUPPLIES: ±13V at 5mA ● 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 +VISO 2 –VISO 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. 20M 8 Sense 2 5 +IP 6 –IP Barrier +VISO Out Filter Channel 1 Out PGA Modulate Demod Rectify Power 28 INPUT SELECT A1 A0 Com1 +0.1V +10V Signal 0 0 1 1 0 1 0 1 GAIN SELECT G 0.5 50 0 1 20M 3 Sense 1 –VISO 10.0V Ref 1 IREF1 7 IREF2 0.100V Current Reference Com 1 Com 1 CKI 26 Com 2 27 VDD (+5) 18 CLK 22 G 19 A0 20 A1 21 RST 23 DCom 2 24 Channel 3 R –VISO 10 VCC (+15) 25 99R VREF 4 MUX Channel 2 Channel 4 A0 A1 O P T O Com 1 Input Side Com 2 C O U P L E Output Side L A T C H SELECT and GAIN RST CLK No Change No Change Latch RESET 1 1 1 0 0 1 ^ X International Airport Industrial Park • Mailing Address: PO Box 11400 Tel: (520) 746-1111 • Twx: 910-952-1111 • Cable: BBRCORP • • 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 1991 Burr-Brown Corporation Printed in U.S.A. October, 1993 SPECIFICATIONS ELECTRICAL At VCC = 15V, VDD = 5V, TA = +25°C, unless otherwise noted. ISC300 PARAMETER ISOLATION Isolation Voltage (VISO) 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) CONDITIONS MIN AC60Hz Continuous AC60Hz Continuous VISO, DC Partial Discharge(1) VISO = Rated 60Hz Cont(2) 500 ±700 700 800 110 TYP ±30 ±0.01 0°C to +70°C VO = –5V to +5V(4) vs Supply (VCC) ±1.5 –40°C to +85°C 35 100 Resistance Range Peak Voltage Impedance: Differential Common Mode Rejection 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 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 < 1kΩ Imbalance Min Load = 1MΩ During Input Fault (VIN < –11V or VIN > 11V) 0 10 66 75 60 ±3 ±50 ±0.025 V/V mV/Ω % ppm/°C % nA pA/°C ±10 ±0.1 500 ±380 V V Ω V MΩ dB dB dB kΩ 3 0.5 10 V V kΩ mVrms mVp-p 3.5 0.5 5 1 2 Hz s s ms ms 100 ±0.1 ±10 14 5 4 11.5 2 50 ±5 10 ±0.1 ±10 External Loading of 100nA No External Load at 5mA Each Supply mV mV µV/°C µV/°C mV/V 75 100 70 ±5.4 TSETT, to within 5% for VIN < 14V VCC Pin No External Load VDD Pin ±200 ±5 ±200 ±5 10 f = 0 to 5kHz Min Load 1MΩ f = 0 to 100kHz Min Load 1MΩ ® ISC300 4 Vrms VPEAK V Vrms dB GΩ || pF µArms 50, 0.5 10 INPUT CURRENT Initial Bias vs Temperature INPUT Voltage Range UNITS 2 || 15 VISO = 240 Vrms 60Hz VIN = 0V G = 0.5 VIN = 0V G = 50 0°C to +70°C G = 0.5 0°C to +70°C G = 50 VCC = 14V to 16V vs Temperature MAX 1 80 13 5 5 ±1 ±20 ±20 ±1 ±20 ±20 16 10 6 3 184 V % ppm/°C ppm/kHr %/V mV % ppm/°C ppm/kHr %/V V mA V mA mW V mA SPECIFICATIONS (CONT) ELECTRICAL At VCC = 15V, VDD = 5V, TA = +25°C, unless otherwise noted. ISC300 PARAMETER CONDITIONS INPUT O/C SENSE Sense Current MIN TYP IS2, Sense 1 = 0V –IS2, Sense 2 = 0V REFERENCE CURRENT Reference Current (IREF1) Reference Currents Ratio MAX µA µA 0.7 0.7 199 200 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 µA % 201 ±0.5 IREF1 : IREF2 CLOCK SYNC CKI Input Voltage - High Level Input Voltage - Low Level Input Current - High Level Input Current - Low Level Input Frequency Input Duty Cycle UNITS 3.5 V V ns ns ns ns ns 1.5 450 20 20 5 5 VCC = 15V VCC = 15V VIL = 11V VCC = 15V VIL = 4V VCC = 15V 11 V V µA µA kHz % 4 350 350 50 45 45 TEMPERATURE RANGE Specification Operating Storage θJA TJ max 55 55 0 0 –40 °C °C °C °C/W °C 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 ABSOLUTE MAXIMUM RATINGS Signal Input Voltage ......................................................................... ±380V Analog Supply Voltage VCC .................................................................. 18V Digital Supply Voltage VDD ..................................................................... 7V Voltage Across Barrier ................................................................. 800Vrms Storage Temperature Range .......................................... –45°C to +100°C Lead Temperature (soldering, 10s) ................................................ +300°C Out Short Circuit Duration ........................................ Continuous to Com 2 Relative Humidity (non-condensing) ............................................. 95% RH 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 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 tSU VDD (+5V) G A0 A1 CLK RST DCom 2 VCC (+15V) CKI Com 2 Out Data tHO tW CLK tW tW RST t REL ® 3 ISC300 THEORY OF OPERATION 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). 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. 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. 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. 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 INPUT SECTION The voltage reference provides 10V, 0.1V and 0V references for channel calibration. The 10V reference is also available externally. 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. Current References Two matched 200µA current references are available for the excitation of RTDs or for use in external signal conditioning circuitry. 9 +VISO 2 –VISO 20M 8 Sense 2 5 Barrier +VISO Out +IP Filter 6 Channel 1 Out PGA Modulate Demod Rectify Power 28 –IP 20M 3 Sense 1 –VISO 10.0V Ref 1 4 7 99R VREF 0.100V IREF1 Current Reference IREF2 Com 1 Com1 Channel 4 A0 A1 O P T O Com 1 Input Side Com 2 C O U P L E Output Side FIGURE 1. ISC300 Block Diagram. ® ISC300 CKI 26 Com 2 27 VDD (+5) 18 CLK 22 G 19 A0 20 A1 21 RST 23 DCom 2 24 Channel 3 R –VISO 10 VCC (+15) 25 MUX Channel 2 4 L A T C H 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. 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. Isolated Supplies Two 13V isolated supplies, capable of supplying 5mA each, are available to power signal conditioning circuitry. 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 0.1µF 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. 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. 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 10Ω resistance value results in a (10 • 200µA) • 50 = 0.1V output; the 500Ω full scale value gives a (500 • 200µA) • 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. 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 0.01µs – 0.1µs 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.” CINT Com 2 CEXT Com 1 R VISO We have designed and characterized the package to yield an inception voltage in excess of 800Vrms so that transient FIGURE 2. Barrier Capacitance. ® 5 ISC300 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. 10µF tantalum capacitors should be used. This will also improve the signal-to-noise ratio. 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. Line Resistance Com 1 Com 1 +In 0Ω to 500 Ω RS – In Filter and MUX Sense 2 20MΩ IREF1 PGA +VISO IREF2 I1 I2 –VISO FIGURE 3. Resistance Measurement Configuration. Sense 1 20MΩ –VISO Line Resistance +In –10V to +10V –In Filter and MUX Sense 2 20MΩ Com 1 FIGURE 4. Voltage Measurement Configuration. ® ISC300 6 PGA +VISO MEASUREMENT CHANNEL CALIBRATION pins of each ISC300 in the system together (see Figure 6). The ISC300 can also be synchronized by an external clock driver. 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. 1 0 50 1 1 +0.1V 0 1 No Change 1 +10V 1 0 Latch 1 ^ Signal 1 1 RESET 0 X CKI CKI CKI CKI CKI CKI N No Change ISC300 0 5 0.5 ISC300 0 4 CLK 0 ISC300 RST Com 1 3 SELECT AND GAIN ISC300 G 2 GAIN SELECT ISC300 A0 1 A1 ISC300 INPUT SELECT Optional Clock Driver FIGURE 6. Synchronizing Multi-ISC300 Applications. System calibration would typically proceed as follows: 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 1MΩ will cause an increase in noise at the carrier frequency and will appear as ripple in the output waveform. 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. APPLICATIONS This section describes the design criteria of various applications of the ISC300. 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) 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 Sense 1 2 J1 1 20MΩ –VISO IREF1 –VISO 3 +In +In –In –In 1 J2 3 Filter and MUX PGA IREF2 –VISO 2 Sense 2 220pF Com 1 Com CKI f = 50kHz 39k Ω Simplified Schematic FIGURE 5. CKI Input. +VISO 20MΩ Com 1 Jumper Mode Voltage J1 J2 1-2 1-2 RTD 2-3 2-3 FIGURE 7. Mode Selection Jumpers. ® 7 ISC300 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. Com 1 +In RS 0V In Figure 8: –In (+In) = –r1 (I1 + I2) – r2I1 (1) (2) (–In) = –r1 (I1 + I2) – R2I2 – r3I2 (1) – (2) I1 I2 = –r2I2 + RSI2 + r3I2 Since r1 = r2 = r3 (LEADS) 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. Com 1 +In RS –VISO T1 –In Com 1 I1 I 1 + I2 I2 T2 +In RS I2 • RS = VIN T3 Output < –5.1V –VISO –In I1 FIGURE 11. +In Open Circuit. I2 Com 1 Output = G • VIN –VISO FIGURE 8. Normal Operation. +In RS +VISO –In Com 1 I1 I2 +In RS +VISO Output > +5.1V –In I1 Output > +5.1V FIGURE 12. –In Open Circuit. I2 –VISO FIGURE 9. RS Open Circuit. ® ISC300 8 –VISO RS Com 1 Com 1 +In +In RS Undefined Undefined –In –In I1 Output Undefined I1 I2 I2 Output Undefined –VISO –VISO FIGURE 13. –In and +In Open Circuit. FIGURE 14. Com 1 Open Circuit. APPLICATIONS FLEXIBILITY 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 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 4 TO 20MA RECEIVER In Figure 17, the ISC300 converts a 4 to 20mA current to an isolated 0 to 5V output. The 6.25Ω resistor converts the 4 to 20mA input to 0.025 to 0.125V. The 125Ω resistor in conjunction with the 200µA 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. 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 • Adjust R2 with 4mA input for 0V output. 6.8nF +VCC Sense 1 100kΩ +In 100kΩ Out 6.8nF ACom 2 +10VIN ±10VOUT OPA27GP 22kΩ +VDD –In 22kΩ ƒ–3dB = 200Hz Sense 2 Logic Control Com 1 DCom 2 FIGURE 15. Isolated Voltage Measurement Channel with Output Filter. ® 9 ISC300 +VCC 1/2 OPA1013 +VSS1 –VSS1 +VSS1 20kΩ VREF1 B Out 10k Ω –VSS1 ACom 2 +VSS1 +VDD +In INA102 –In 1kΩ Logic Control 1kΩ –VSS1 100kΩ Com 1 1kΩ DCom 2 1kΩ 100kΩ +VSS1 A –VSS1 1/2 OPA1013 FIGURE 16. Isolated Instrument Bridge System. +VCC R1 +In Out 0 to 5V 125Ω 20Ω 4 to 20mA 6.25Ω ACom 2 10Ω 100Ω 220Ω R2 10Ω 330Ω +VDD –In IREF1 +VDD Com 1 FIGURE 17. Isolated 4 to 20mA receiver (0 to 5V output). ® ISC300 10 DCom 2 +VCC +VSS1 –VSS1 IREF2 Out ACom 2 +VSS1 +VDD +In INA102 –In –VSS1 Logic Control IREF1 Com 1 DCom 2 FIGURE 18. Temperature Measurement Using Thermocouple with Small Span. +VCC +VSS1 –VSS1 IREF2 Out ACom 2 +VSS1 +VDD +In INA102 –In 4990Ω 30Ω 100Ω –VSS1 Logic Control IREF1 Com 1 DCom 2 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. ® 11 ISC300