ALD1000 Precision Programmable CURRENT/VOLTAGE TRANSMITTER F

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ALD1000 Precision Programmable CURRENT/VOLTAGE TRANSMITTER F

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ALD1000
Precision Programmable CURRENT/VOLTAGE TRANSMITTER
FEATURES
SWITCHABLE OUTPUT ±10V 4-20mA DRIVES 1000 20mA VOLTAGE CURRENT SENSE GROUND NOISE SUPPRESSION ERROR DETECTION FLAG OUTPUT DISABLE ACCURACY: 0.05% WIDE SUPPLY RANGE: ±11V +24/-15V
APPLICATIONS
PROGRAMMABLE CONTROLLERS STANDARDIZED OUTPUTS TERMINATION PANELS INDUSTRIAL PROCESS CONTROL PROGRAMMABLE CURRENT SOURCE MOTOR CONTROL SYSTEMS BASED INSTRUMENTATION CONDITIONER STANDARD SENSOR OUTPUTS TEST EQUIPMENT DRIVER
Phase Compensation Voltage Error Indication
DESCRIPTION
This product monolithic programmable voltage-tocurrent voltage-to-voltage analog line driver circuit. convert ±10V input into either output voltage current with remote sensing. provides drive external transistors boost output current greater than ±25mA levels. Current voltage sensing performed simultaneously. Current sensing achieved through single external sense resistor. Voltage sensing performed directly across load. logic inputs provide both output disable switching between constant current constant voltage output functions. open collector output provides error flag open circuit loads. output disable function allows full control output even during power-on power-off sequencing. instrumentation amplifiers designed insure that load noise circulated within control loop.
Phase
Sense
Output Disable Input Select Internal Drive VIN2 External Drive Open-Loop Gain Control External Drive
VIN1
Gain Control
Provide Closed-Loop Gain Control
Input Over-Voltage Protection
International Airport Industrial Park Mailing Address: 11400, Tucson, 85734 Street Address: 6730 Tucson Blvd., Tucson, 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
1996 Burr-Brown Corporation
PDS-1292A
Printed U.S.A. October, 1996
SPECIFICATIONS
24V, 15V, TAMB 25°C, 2N2222, 2N2907 external transistors, unless otherwise noted. ALD1000U PARAMETER TRANSMITTER SWOP INPUTS Linear Range Linear Range Input Bias Current OUTPUT Positive Overvoltage Sense Negative Overvoltage Sense Positive Overcurrent Sense Negative Overcurrent Sense LOGIC INPUTS Logic Logic High LOGIC OUTPUTS Logic High Logic Internal Drive Transistors Load CONDITIONS UNITS
Internal Drive Transistors
19.5 -10.5
Logic Supply with pull-up resistor
OUTPUT-VOLTAGE MODE (Gain unless otherwise specified) Span Error Span Drift Linear Range 0.1% Linear Range 0.1% Output Current Internal Drive Transistors Output Current Internal Drive Transistors Short-Circuit Current Internal Drive Transistors Short-Circuit Current Internal Drive Transistors Non-Linearity Initial Offset Voltage-RTI Offset Voltage Temperature OUTPUT-CURRENT MODE (Gain with shunt resistor unless otherwise specified) Span Error Span Drift Gain 1(1) Output Current Internal Drive Transistors Output Current Internal Drive Transistors Compliance Compliance Offset Current Offset Current INSTRUMENTATION AMPLIFIERS RLOAD INPUTS Linear Input Voltage Linear Input Voltage Common-Mode Input Voltage Common-Mode Input Voltage Input Bias Current Initial Offset Voltage CMRR OUTPUTS (with Load) Output Voltage Output Voltage Short Circuit Current Short Circuit Current GAIN EQUATION (gain 1+50k/RG) Gain Error, Non-Linearity,
ppm/°C
0.005
0.05
µV/°C ppm/°C
0.004 0.008 0.02
%±FS %±FS %±FS %±FS %±FS %±FS
ALD1000
SPECIFICATIONS
PARAMETER FREQUENCY RESPONSE Slew Rate SETTLING TIME, 0.01% POWER SUPPLY Quiescent Current TEMPERATURE RANGE Operating Storage
(CONT)
ALD1000U CONDITIONS UNITS
24V, 15V, TAMB 25°C, 2N2222, 2N2907 external transistors, unless otherwise noted.
±10V,
V/µS
Internal Drive Transistors
+150
NOTES: Gain drift depends tempco factor gain equation when gain greater than External Drive capacity varies with configuration. Application Note.
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (±VS) +25V, -18V Inputs ±40V SWOP Inputs Logic Inputs +VS, 0.5V Junction Temperature 150°C Storage Temperature -65°C +150°C Lead Temperature (soldering, 10s) +300°C Output Short-to-Ground 25°C Continuous
ELECTROSTATIC DISCHARGE SENSITIVITY
This integrated circuit damaged ESD. Burr-Brown recommends that integrated circuits handled with appropriate precautions. Failure observe proper handling installation procedures cause damage. damage range from subtle performance degradation complete device failure. Precision integrated circuits more susceptible damage because very small parametric changes could cause device meet published specifications.
PACKAGE/ORDERING INFORMATION
PRODUCT ALD1000U PACKAGE 28-Pin SOIC PACKAGE DRAWING NUMBER(1)
NOTE: detailed drawing dimension table, please data sheet, Appendix Burr-Brown Data Book.
information provided herein believed reliable; however, BURR-BROWN assumes responsibility inaccuracies omissions. BURR-BROWN assumes responsibility this information, such information shall entirely user's risk. Prices specifications subject change without notice. patent rights licenses circuits described herein implied granted third party. BURR-BROWN does authorize warrant BURR-BROWN product life support devices and/or systems.
ALD1000
CONFIGURATION
View 28-Lead SOIC
Disable Select ACOM VOUT1 VINP1 RGB1 RGA1 VINN1
VERR Bias VOUT2 VINP2 RGB2 RGA2 VINN2
ASSIGNMENTS
NAME Disable Select ACOM VOUT1 VINP1 RGB1 RGA1 VINN1 VINN2 RGA2 RGB2 VINP2 VOUT2 Bias VERR DESCRIPTION Power ground pin. signal puts internal drive high impedance state limits external drive capacity. Selects SWOP input. signal selects inputs external compensation capacitor. external compensation capacitor. Non-inverting input SWOP Inverting input SWOP Signal ground instrumentation amplifiers. Positive power supply voltage. Output instrumentation amplifier Non-inverting input instrumentation amplifier Gain resistor instrumentation amplifier Gain resistor instrumentation amplifier Inverting input instrumentation amplifier Inverting input instrumentation amplifier Gain resistor instrumentation amplifier Gain resistor instrumentation amplifier Non-inverting input instrumentation amplifier Output instrumentation amplifier Negative power supply voltage. Inverting input SWOP Non-inverting input SWOP Inverting input (emitter) output transconductance amplifier. Base drive external, PNP, driver transistor (optional). Base drive external, NPN, driver transistor (optional). Output (collector) output transconductance amplifier. Open collector output indicating internal overcurrent condition. Open collector output indicating overvoltage condition.
ALD1000
TYPICAL PERFORMANCE CURVES
+25°C; 24V, -15V, unless otherwise noted.
STEP RESPONSE CURRENT FEEDBACK MODE
STEP RESPONSE VOLTAGE FEEDBACK
Output
Figure 400, 100nf external comp capacitor
Output
Figure 400, 100nf External Comp Capacitor
Time (µs) Time (µs)
STEP RESPONSE VOLTAGE FEEDBACK 1.0E-08
COMPENSATION CAPACITOR LOAD CAPACITANCE
Compensation Capacitor
1.0E-09
Output
Time (µs) Figure 400, 100nf 420pf Compensation Capacitor
1.0E-10 Gain 1.0E-11 1.0E-12 1.0E-11 1.0E-10 1.0E-09 1.0E-08 1.0E-07 1.0E-06 Load Capacitance
STEP RESPONSE CURRENT FEEDBACK MODE
Output
Output
STEP RESPONSE LOAD VOLTAGE FEEDBACK MODE
1000 1500 2000 2500 3000 3500 4000 4500 Time (µs) Figure 400, Comp Capacitor
Figure 400, Comp 2.2nf
Time (µs)
ALD1000
TYPICAL PERFORMANCE CURVES (CONT)
+25°C; +24V, -15V, unless otherwise noted.
STEP RESPONSE CURRENT FEEDBACK MODE
STEP RESPONSE VOLTAGE FEEDBACK MODE
Output Output
1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Time (µs) Figure 400,
Figure 220, Compensation Capacitor
1000 1200 1400 1600 1800 Time (µs)
STEP RESPONSE VOLTAGE FEEDBACK MODE
STEP RESPONSE VOLTAGE FEEDBACK MODE
Output
Output
Figure 220, 2.2nf Compensation Capacitor
Figure
1000 1200 1400 1600 1800 Time (µs)
Time (µs)
STEP RESPONSE WITH LOAD CURRENT FEEDBACK
STEP RESPONSE WITH LOAD VOLTAGE FEEDBACK
Output
Output
Figure 15pf Comp Capacitor, 5.5k
Time (µs)
Figure 15pf comp capacitor, 5.5k
Time (µs)
ALD1000
TYPICAL PERFORMANCE CURVES (CONT)
+25°C; +24V, -15V, unless otherwise noted.
COMMON-MODE REJECTION FREQUENCY Gain
GAIN FREQUENCY 1000 Instrumentation Amplifiers Gain
Commom-Mode Rejection (dB)
Gain
Gain
Instrumentation Amplifiers with ±10V input Gain Gain
Gain
100k Frequency (Hz)
Frequency (kHz)
1000
10000
INPUT BIAS CURRENT INPUT VOLTAGE
Common-Mode Voltage
INPUT COMMON-MODE RANGE OUTPUT VOLTAGE Gains
Bias Current (mA)
Gain Gain
Gain
Gain
Input Voltage
Output Voltage
BASIC OPERATION
ALD1000 FUNCTIONAL BLOCKS typical ALD1000 control loop comprises three primary functional blocks (see Figure current transmitter (XTR), load, instrumentation amplifier (IA). further viewed divided into switchable input operational amplifier (SWOP amp), voltage current, transconductance amplifier (TA). Each these blocks plays role dynamic performance control loop, particularly terms loop stability with reactive loads. CURRENT TRANSMITTER (XTR) produces forward gain necessary error amplification. also controls frequency response which must adjusted balance trade-off between step response stability when driving reactive loads. Within SWOP serves input stage. amplifies error between input output signals produce precise signal drive load.
SWOP pairs inputs provide flexibility application. SELECT logic input switch between input feedback signals. Take care, however, insure that loop remains stable switching between current voltage feedback. ALD1000 handles wide range load conditions either voltage current feedback application. frequency characteristics potential load conditions vary widely. accommodate these varying frequency characteristics includes compensation network. consists simple resistor divider network which forms single pole, high pass, filter when compensation capacitor connected externally. transconductance amplifier converts output voltage SWOP into output current drive load. Whether used current feedback voltage feedback loop, ALD1000 transmitter should viewed source current voltage. voltage loop, output current converted feedback voltage load. current loop output current converted feedback voltage shunt resistor. external, gain resistor, tied (Pin Figure sets voltage current ratio.
ALD1000
VERR
+24V
Sense
Input Select Input Signal
Select
Freq. Comp.
2N2907
Local Shunt
SWOP Loop Gain
2N2222
Disable
VINN1
-15V
Monitor Current VOUT1
ACOM Monitor Voltage VOUT2 VINN2 Remote Load RGB2 RGA2 VINP2 VINP1
0-10 0.8-4 2-10 0-10
IOUT 0-10mA 0-50mA 4-20mA 10-50mA
VOUT
SELECT
DISABLE
0-5V 0-10V ±10V
FIGURE
ALD1000
INSTRUMENTATION AMPLIFIERS (IA) ALD1000 includes two, general purpose, uncommitted, 3-op amp, instrumentation amplifiers (see Figure connected common power supply operate full supply voltage. They share same analog common reference. Otherwise they configured independently maximum flexibility. instrumentation amplifier senses feedback signal, reduces common-mode component, scales level required. more comprehensive discussion instrumentation amplifiers follows later section.
VOLTAGE ERROR INDICATION VERR error signal triggers when voltage (pin exceeds Positive Overvoltage Sense Negative Overvoltage Sense (see SPECIFICATIONS) internal thresholds. When external transistors used without connecting them shown Figure load voltage cannot detected. logic signal will generally trigger error state (low). However, consider indeterminate under these conditions.
INSTRUMENTATION AMPLIFIERS
SETTING GAIN gain connecting single, external resistor, Figure between gain pins.
ALD1000 LOGIC
logic inputs used SWOP select disable functions simple, differential pair comparators shown Figure logic outputs open collector transistors with their emitters ground (pin
Logic Input Internal Logic
Internal Logic Threshold
INPUT PROTECTION inputs ALD1000 instrumentation amplifiers individually protected against over-voltage. Internal circuitry each input provides series impedance under normal signal conditions. input overloaded, protection circuitry limits input current safe value approximately 5ma. Refer typical performance curve "Input Bias Current Input Voltage." inputs protected even power supplies disconnected turned off. INPUT OVERLOAD INPUT COMMON-MODE RANGE
FIGURE Simplified Diagram Internal ALD1000 Logic Input Circuitry.
linear voltage range input circuitry ALD1000 instrumentation amplifiers from approximately 0.6V below positive supply above negative supply. However, output swing input amplifiers
VIN-
Over-Voltage Protection
VIN+ Over-Voltage Protection
VOUT
FIGURE Simplified Schematic Instrumentation Amplifiers. Resistor Controls Gain.
ALD1000
limit this range when differential input voltage causes output voltage increase. Thus, linear common-mode range relates output voltage complete amplifier. This behavior also depends supply voltage-see performance curve "Input Common-Mode Range Output Voltage." combination significant differential signal high common-mode voltage occurs current feedback configuration reduces common-mode range. Exceeding common-mode range results reduced output voltage. When this occurs feedback loop longer balance. forward gain ALD1000 amplifies this false error signal, output voltage tries increase, this holds overloaded condition. ALD1000 applies defenses against this problem. First, there resistor series with transmitter output. This resistor, which primarily provides protection from over-voltage damage output terminal, acts limit output swing under high current conditions. Second, ALD1000's error detection circuitry signals when transmitter output voltage exceeds rating. This serves detect potential lock condition. Limiting transmitter's output swing within instrumentation amplifier's input range allows loop recover without reducing input signal should transient voltage level exceed common-mode input range. However, common-mode range instrumentation amplifiers varies with application specific factors. Lock-up occur. application designer must provide defenses against this condition where warranted. USING INSTRUMENTATION AMPLIFIERS WITH FLOATING SIGNAL SOURCE input impedance ALD1000 instrumentation amplifiers very high-about 106. Within feedback loop, shown examples, this characteristic acts minimize errors caused loading feedback signal. However, used amplifier thermocouple, microphone, other isolated signal source path needed input bias current. This current nominally about 100nA. Without return path inputs will float potential that exceeds common-mode range amplifier. Figure
insure adequate transient response loop stability: loop gain phase. Together loop gain phase phase margin which defines dynamic performance. Loop gain product forward voltage current ratio, load impedance, gain. input error voltage converted output current. output current converted feedback voltage load impedance. feedback voltage gained feedback three blocks affect loop stability. gain resistor, which connected ALD1000, adjusts voltage current relationship. Increasing this resistor decreases loop gain. This, turn, increases phase margin slows step response. This resistor will typically between 2500. voltage feedback loop frequency which loop gain starts roll decreases with increasing capacitance. necessary compensate loss bandwidth caused load capacitance. compensation network provides this capability. Typical performance curve "Compensation Capacitor Load Capacitance" illustrates typical compensation capacitor values load capacitance varying from 1µf. Exact capacitor values will vary with load resistance, gain resistor value, gain, variability open loop gain ALD1000 SWOP amp. This curve provides starting point empirical selection compensation capacitor value. effect described above much less significant with current feedback loop since shunt resistor's capacitance easily controlled. current feedback loop will more robust when load conditions unknown varying. LOOP STABILITY INSTRUMENTATION AMPLIFIERS frequency characteristics gain instrumentation amplifiers affect loop stability when they used feedback loop. There main contributions. First, gain directly multiplies loop gain. result high gains reduce phase margin. Second, when input exceeds range output longer provide necessary feedback. This result lock condition. Both these situations discussed further below. LOOP GAIN INSTRUMENTATION AMPLIFIERS ALD1000 designed feedback loop. When instrumentation amplifiers used feedback amplifier gain directly contributes loop gain. loop become unstable loop gain large. Conversely, possible stabilize difficult loop reducing gain Refer Figure this circuit ALD1000 configured current loop with shunt resistor. 20ma full scale current through shunt results feedback signal. must remove common-mode level from shunt voltage scale resulting differential signal input signal level.
LOOP STABILITY
stability closed loop system such intended application ALD1000 requires adequate phase margin. contrast, excessive phase margin will reduce circuit's transient response fast changing signals. intent this section give insight into ALD1000 circuits blocks affect dynamic performance. Selection loop architecture compensation then done empirically. LOOP STABILITY There critical parameters that must controlled
ALD1000
USING ALD1000 WITH EXTERNAL DRIVE TRANSISTORS
Signal Load
12.5k
ALD1000
Power dissipated internal driver stage affects built-in instrumentation amplifiers compromising their accuracy. External transistors reduce internal power dissapation. external transistors configured current sources. transistor delivers positive current. supplies negative drive. Either both used. example 20ma current loop only require transistor since negative current drive required. Figure Degeneration resistors required (refer Figure value degeneration resistors will affect stability, load sharing with internal driver devices, current limit value. These issues covered more detail below. EXTERNAL TRANSISTORS CURRENT LIMIT VALUE ALD1000 contains circuitry prevent damage internal components excess current. When using internal driver stage itself, current load limited about 20ma room temperature. When using external drivers, current limit depends, approximately, load sharing ratio between internal external transistors. Figure illustrates circuit relationship between current limit circuitry external drive transistors. DEGENERATION RESISTORS degeneration resistors, Figure control load sharing between internal external transistors. Choose resistor values measuring load current, current through external transistor, calculating current being supplied internal drive. LOOP STABILITY DEGENERATION RESISTORS Loop stability depends loop gain. Because degeneration resistors affect voltage current ratio loop value these resistors also affect loop gain thus stability. Smaller resistor values will increase loop gain. necessary compensate this adjusting value gain resistor connected Pin, Figure EXTERNAL TRANSISTORS OUTPUT VOLTAGE SWING
FIGURE Simplified Block Diagram 20ma Current Loop. Gain Match Full Scale Shunt Signal Full Scale Input Signal. Here input signal affects loop stability. full scale input signal would require gain lower input signal, shown Figure allows gain reduced This results lower loop gain increased phase margin. Note that possible reduce gain less than using voltage divider output. VOLTAGE FEEDBACK INSTRUMENTATION AMPLIFIERS instrumentation amplifiers used remote sensing voltage feedback loop illustrated Figure Here instrumentation amplifier tends reject small ground potential differences between source load. voltage loop, however, more sensitive reactive load impedance than current loop. ALD1000 emitter resistor compensation capacitor need selected specific load conditions. Voltage feedback appropriate variable load conditions.
Signal
RCOMP
CCOMP
Load
ALD1000
FIGURE Simplified Block Diagram ALD1000 Voltage Feedback.
output voltage swing must limited within input range instrumentation amplifiers. resistor shown Figure limits output swing under high current conditions. Resistor performs this function with external transistors. must sized limit output swing, expected full load, within input range instrumentation amplifiers. Refer section instrumentation amplifiers further information.
ALD1000
Positive Current Limit
Load
Signal
Negative Current Limit
ALD1000 OUTPUT STAGE
FIGURE Simplified Schematic Showing External Drive Transistors. Provide Degeneration that Affects Current Limit Loop Stability. Controls Transconductance Amplifier Gain Affecting Loop Stability Transient Response. Text.
ALD1000
COMP
2N2907
2N2222
12.5k
ALD1000
FIGURE Using External Transistors Without Internal Drive. Note that Overvoltage Condition Detected.
COMP
2.5k
12.5k
ALD1000
FIGURE 8.Using Internal Drive Transistors.
ALD1000
100pf
2N2907
3.7k Disable
ALD1000
FIGURE Sharing Load Between Internal Drive Transistors Positive External Drive Transistors Increase Load Capacity. Similiar Configuration Possible with Negative External Drive Transistor.
COMP
Load
Sense Output
ALD1000
Differential Input Signal
FIGURE Showing Flexibility Application: Using Direct Voltage Feedback Free Both IAs; Using Differential Input; Using Grounded Input Provide State; Providing Ground Path Bias Current With Thermocouple.
ALD1000

ALD1000 Precision Programmable CURRENT/VOLTAGE TRANSMITTER F

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