ALD1000

ALD1000 BURR-BROWN | Alldatasheet

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Technical content

International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111 • Twx: 910-952-1111 Internet: http://www.burr-brown.com/ • FAXLine: (800) 548-6133 (US/Canada Only) • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132 Precision Programmable CURRENT/VOLTAGE TRANSMITTER

FEATURES

G SWITCHABLE OUTPUT ±10V OR 4-20mA G DRIVES 1000Ω || 1µF AT 20mA G VOLTAGE AND CURRENT SENSE G GROUND NOISE SUPPRESSION G ERROR DETECTION FLAG G OUTPUT DISABLE G ACCURACY: 0.05% max G WIDE SUPPLY RANGE: ±11V TO +24/–15V

APPLICATIONS

G PROGRAMMABLE CONTROLLERS G STANDARDIZED OUTPUTS FOR TERMINATION PANELS G INDUSTRIAL PROCESS CONTROL G PROGRAMMABLE CURRENT SOURCE G MOTOR CONTROL SYSTEMS G PC AND VME BASED INSTRUMENTATION G CONDITIONER FOR STANDARD SENSOR OUTPUTS G TEST EQUIPMENT PIN DRIVER

DESCRIPTION

This product is a monolithic programmable voltage-to- current or voltage-to-voltage analog line driver circuit. It can convert a ±10V input into either an output voltage or current with remote sensing. It provides drive for external transistors to boost output current to greater than ±25mA levels. Current and voltage sensing can be performed simulta- neously. Current sensing is achieved through a single external sense resistor. Voltage sensing is performed directly across the load. The logic inputs provide for both output disable and switching between constant current or constant voltage output functions. An open collector output provides an error flag for open circuit loads. The output disable function allows full control of the output even during power-on and power-off sequencing. The instrumentation amplifiers are de- signed to insure that load noise is not circulated within the control loop. ALD1000 ALD1000 100Ω V Sense Phase IA1 IA2 Phase Compensation Voltage Error Indication External PNP Drive Internal Drive External NPN Drive Open-Loop Gain Control IAs Provide Closed-Loop Gain Control IA Gain Control VIN1 VIN2 Input Select Output Disable Input Over-Voltage Protection ©1996 Burr-Brown Corporation PDS-1292A Printed in U.S.A. October, 1996

At +VS = 24V, –VS = 15V, TAMB = 25°C, and 2N2222, 2N2907 external transistors, unless otherwise noted. ALD1000U PARAMETER CONDITIONS MIN TYP MAX UNITS TRANSMITTER SWOP INPUTS Linear Range Min Internal Drive Transistors –10 V Linear Range Max 5mA Load V Input Bias Current pA XTR OUTPUT Positive Overvoltage Sense 19.5 V Negative Overvoltage Sense Internal Drive Transistors –10.5 V Positive Overcurrent Sense +25 mA Negative Overcurrent Sense –15 mA LOGIC INPUTS Logic Low 0.8 V Logic High 4.0 2.6 V LOGIC OUTPUTS Logic High 5V Logic Supply 4.0 V Logic Low with 10k pull-up resistor 0.8 V OUTPUT—VOLTAGE MODE (Gain = 1 unless otherwise specified) Span Error 0.5 Span Drift ppm/°C of FS Linear Range Min 0.1% of FS –10 Linear Range Max 0.1% of FS Output Current Min Internal Drive Transistors mA Output Current Max Internal Drive Transistors mA Short-Circuit Current Internal Drive Transistors mA Short-Circuit Current Internal Drive Transistors –15 mA Non-Linearity 0.005 0.05 Initial Offset Voltage—RTI mV Offset Voltage vs Temperature µV/°C OUTPUT—CURRENT MODE (Gain = 5 with 50Ω shunt resistor unless otherwise specified) Span Error Span Drift Gain = 1(1) ppm/°C of FS Output Current Min Internal Drive Transistors(2) mA Output Current Max Internal Drive Transistors(2) mA Compliance Min –10 V Compliance Max V Offset Current Min –25 µA Offset Current Min µA INSTRUMENTATION AMPLIFIERS RLOAD = 10k IA INPUTS Linear Input Voltage Min –10 V Linear Input Voltage Max V Common-Mode Input Voltage Min VIN = 0 –10 V Common-Mode Input Voltage Max VIN = 0 V Input Bias Current 100 nA Initial Offset Voltage G = 1 mV CMRR G = 10 100 IA OUTPUTS (with 10k Load) Output Voltage Max V Output Voltage Min –10 V + Short Circuit Current mA – Short Circuit Current –12 mA GAIN EQUATION (gain = 1+50k/RG) Gain Error, G = 1 0.3 %±FS G = 5 0.6 %±FS G = 100 0.8 %±FS Non-Linearity, G = 1 0.004 %±FS G = 5 0.008 %±FS G = 100 0.02 %±FS

G = 1 700 kHz G = 5 400 kHz G = 100 kHz Slew Rate VO = ±10V, G = 10 V/µS SETTLING TIME, 0.01% G = 1 µS G = 5 µS G = 100 µS POWER SUPPLY Quiescent Current Internal Drive Transistors mA TEMPERATURE RANGE Operating –40 +85 Storage –65 +150 NOTES: (1) Gain drift depends on tempco of 50K factor on gain equation when gain is greater than 1. (2) External Drive capacity varies with configuration. See Application Note. ABSOLUTE MAXIMUM RATINGS SPECIFICATIONS (CONT) At +VS = 24V, –VS = 15V, TAMB = 25°C, and 2N2222, 2N2907 external transistors, unless otherwise noted. 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. PACKAGE/ORDERING INFORMATION PACKAGE DRAWING PRODUCT PACKAGE NUMBER(1) ALD1000U 28-Pin SOIC 217 NOTE: (1) For detailed drawing and dimension table, please see end of data sheet, or Appendix C of Burr-Brown IC Data Book. ELECTROSTATIC DISCHARGE SENSITIVITY This integrated circuit can be damaged by ESD. Burr-Brown recommends that all integrated circuits be handled with ap- propriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.

PIN # NAME Power ground pin. Disable A 5V signal puts the internal drive in a high impedance state and limits the external drive capacity. Select Selects the SWOP amp input. A 5V signal selects inputs N1 and P1. CC2 CC1 and CC2 are for the external compensation capacitor. CC1 CC1 and CC2 are for the external compensation capacitor. Non-inverting input to the XTR SWOP amp 1. Inverting input to the XTR SWOP amp 1. ACOM Signal ground for the instrumentation amplifiers. +VS Positive power supply voltage. VOUT1 Output of the instrumentation amplifier 1. VINP1 Non-inverting input to instrumentation amplifier 1. RGB1 Gain set resistor for instrumentation amplifier 1. RGA1 Gain set resistor for instrumentation amplifier 1. VINN1 Inverting input of instrumentation amplifier 1. VINN2 Inverting input of instrumentation amplifier 2. RGA2 Gain set resistor for instrumentation amplifier 2. RGB2 Gain set resistor for instrumentation amplifier 2. VINP2 Non-inverting input to instrumentation amplifier 2. VOUT2 Output of the instrumentation amplifier 2. –VS Negative power supply voltage. Inverting input to the XTR SWOP amp 2. Non-inverting input to the XTR SWOP amp 2. E Inverting input (emitter) of the output transconductance amplifier. XP Base drive for an external, PNP, driver transistor (optional). XN Base drive for an external, NPN, driver transistor (optional). C Output (collector) of the output transconductance amplifier. Bias Open collector output indicating an internal overcurrent condition. VERR Open collector output indicating an overvoltage condition. PIN CONFIGURATION Top View 28-Lead SOIC XTR GND Disable Select CC2 CC1 ACOM +VS VOUT1 VINP1 RGB1 RGA1 VINN1 VERR Bias C XN XP E –VS VOUT2 VINP2 RGB2 RGA2 VINN2 IA IA TA

TYPICAL PERFORMANCE CURVES (CONT) At TA = +25°C; +VS = +24V, –VS = –15V, unless otherwise noted. BASIC OPERATION ALD1000 FUNCTIONAL BLOCKS The typical ALD1000 control loop comprises three primary functional blocks (see Figure 1): the current transmitter (XTR), the load, and the instrumentation amplifier (IA). The XTR can be further viewed as divided into the switchable input operational amplifier (SWOP amp), and the voltage to current, transconductance amplifier (TA). Each of these blocks plays a role in the dynamic performance of the control loop, particularly in terms of loop stability with reactive loads. THE CURRENT TRANSMITTER (XTR) The XTR produces the forward gain necessary for error amplification. It also controls the frequency response which must be adjusted to balance the trade-off between step response and stability when driving reactive loads. Within the XTR the SWOP amp serves as the input stage. It amplifies the error between the input and output signals to produce a precise signal to the TA to drive the load. The SWOP amp has two pairs of inputs to provide flexibility of application. The SELECT logic input can switch between two input and feedback signals. Take care, however, to insure that the loop remains stable if switching between current and voltage feedback. The ALD1000 handles a wide range of load conditions in either a voltage or current feedback application. The fre- quency characteristics of the potential load conditions vary widely. To accommodate these varying frequency character- istics the XTR includes a compensation network. It consists of a simple resistor divider network which forms a single pole, high pass, RC filter when a compensation capacitor is connected externally. The transconductance amplifier converts the output voltage of the SWOP amp into an output current to drive the load. Whether used in a current feedback or a voltage feedback loop, the ALD1000 transmitter should be viewed as a source of current not voltage. In a voltage loop, the output current is converted to a feedback voltage by the load. In a current loop the output current is converted to a feedback voltage by the shunt resistor. The external, XTR gain resistor, tied to E (Pin 23, Figure 1), sets the voltage to current ratio. 1000 100 0.1 Gain GAIN vs FREQUENCY 100 1000 10000 Frequency (kHz) Gain = 5 Gain = 1 Gain = 100 Instrumentation Amplifiers –10 Bias Current (mA) INPUT BIAS CURRENT vs INPUT VOLTAGE –40 –30 –20 –10 Input Voltage (V) Gain = 100 Gain = 1 Gain = 100 Gain = 1 Commom-Mode Rejection (dB) COMMON-MODE REJECTION vs FREQUENCY Frequency (Hz) 120 100 100 10k 100k 10M Gain = 100 Gain = 5 Gain = 1 Instrumentation Amplifiers with ±10V input –10 –15 Common-Mode Voltage INPUT COMMON-MODE RANGE vs OUTPUT VOLTAGE –15 –10 Output Voltage G = 10 G = 10 G = 1 All Gains G = 1

0.8-4 4-20mA 2-10 10-50mA 0-5 0-5V 0-10 0-10V ±5V ±10 ±10V X OFF OFF X FIGURE 1. 100Ω 100Ω 20Ω 400Ω 20Ω XP XN C 40kΩ 25kΩ 40kΩ 40kΩ 40kΩ 25kΩ 40kΩ 40kΩ 25kΩ 25kΩ 40kΩ 40kΩ 50kΩ Loop Gain Local Shunt Remote Load –15V +5V +24V Input Select Input Signal 10kΩ 10kΩ VERR Disable Freq. Comp. XTR GND Select SWOP IAs 1kΩ VOUT1 VOUT2 ACOM Monitor Voltage Monitor Current VINN2 VINP2 VINN1 VINP1 RGA2 RGB2 TA XTR 2N2907 2N2222 V Sense

insure adequate transient response and loop stability: loop gain and phase. Together loop gain and phase set the phase margin which defines dynamic performance. Loop gain is the product of the forward voltage to current ratio, the load impedance, and the IA gain. The input error voltage is converted to an output current. The output current is converted to a feedback voltage by the load impedance. The feedback voltage is gained up by the feedback IA. All three blocks affect loop stability. The XTR gain resistor, which is connected to the E pin of the ALD1000, adjusts the voltage to current relationship. In- creasing this resistor decreases loop gain. This, in turn, increases phase margin and slows step response. This resis- tor will typically be between 250Ω and 2500Ω. In a voltage feedback loop the frequency at which the loop gain starts to roll off decreases with increasing capacitance. It is necessary to compensate for the loss of bandwidth caused by load capacitance. The compensation network provides this capability. Typical performance curve “Com- pensation Capacitor vs Load Capacitance” illustrates typical compensation capacitor values for load capacitance varying from 1pf to 1µf. Exact capacitor values will vary with the load resistance, the XTR gain resistor value, IA gain, and variability of the open loop gain of the ALD1000 SWOP amp. This curve provides a starting point for empirical selection of the compensation capacitor value. The effect described above is much less significant with a current feedback loop since the shunt resistor’s capacitance can be easily controlled. The current feedback loop will be more robust when load conditions are unknown or varying. LOOP STABILITY AND THE INSTRUMENTATION AMPLIFIERS The frequency characteristics and gain of the instrumenta- tion amplifiers affect loop stability when they are used in a feedback loop. There are two main contributions. First, the IA gain directly multiplies loop gain. As a result high IA gains reduce phase margin. Second, when the input exceeds the IA range the IA output can no longer provide the necessary feedback. This can result in a lock condition. Both of these situations are discussed further below. LOOP GAIN AND THE INSTRUMENTATION AMPLIFIERS The ALD1000 is designed for use in a feedback loop. When one of the instrumentation amplifiers is used as the feedback amplifier its gain directly contributes to loop gain. The loop can become unstable if the loop gain is too large. Con- versely, it may be possible to stabilize a difficult loop by reducing the gain of the IA. Refer to Figure 4. In this circuit the ALD1000 is configured in a current loop with a 50Ω shunt resistor. A 20ma full scale current through the 50Ω shunt results in a 1V feedback signal. The IA must remove the common-mode level from the shunt voltage and scale the resulting differential signal up to the input signal level. limit this range when a differential input voltage causes the output voltage to increase. Thus, the linear common-mode range relates to the output voltage of the complete amplifier. This behavior also depends in supply voltage—see perfor- mance curve “Input Common-Mode Range vs Output Volt- age.” The combination of a significant differential signal and a high common-mode voltage as occurs in the current feed- back configuration reduces the common-mode range. Ex- ceeding the common-mode range results in a reduced IA output voltage. When this occurs the feedback loop can no longer balance. The forward gain of the ALD1000 amplifies this false error signal, the output voltage tries to increase, and this holds the IA in an overloaded condition. The ALD1000 applies two defenses against this problem. First, there is a 100Ω resistor in series with the transmitter output. This resistor, which primarily provides protection from over-voltage damage to the output terminal, acts to limit the output swing under high current conditions. Sec- ond, the ALD1000’s error detection circuitry signals when the transmitter output voltage exceeds rating. This serves to detect a potential lock condition. Limiting the transmitter’s output swing to within the instru- mentation amplifier’s input range allows the loop to recover without reducing the input signal should a transient voltage level exceed the common-mode input range. However, the common-mode range of the instrumentation amplifiers var- ies with application specific factors. Lock-up can occur. The application designer must provide defenses against this condition where it is warranted. USING THE INSTRUMENTATION AMPLIFIERS WITH A FLOATING SIGNAL SOURCE The input impedance of the ALD1000 instrumentation am- plifiers are very high—about 106Ω. Within a feedback loop, as shown in the examples, this characteristic acts to minimize errors caused by loading of the feedback signal. However, if used as an amplifier for a thermocouple, micro- phone, or other isolated signal source a path is needed for the input bias current. This current is nominally about 100nA. Without a return path the inputs will float to a potential that exceeds the common-mode range of the amplifier. See Figure 10. LOOP STABILITY The stability of a closed loop system such as the intended application of the ALD1000 requires adequate phase mar- gin. In contrast, excessive phase margin will reduce the circuit’s transient response to fast changing signals. It is the intent of this section to give an insight into how the ALD1000 circuits blocks affect dynamic performance. Selection of the loop architecture and compensation can then be done em- pirically. LOOP STABILITY AND THE XTR There are two critical parameters that must be controlled to

FIGURE 6. Simplified Schematic Showing the Use of External Drive Transistors. R1 and R2 Provide Degeneration that Affects and Transient Response. See the Text.