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PDF XTR108 Data sheet ( Hoja de datos )
| Número de pieza | XTR108 | |
| Descripción | TWO-WIRE TRANSMITTER | |
| Fabricantes | Burr-Brown Corporation | |
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Hay una vista previa y un enlace de descarga de XTR108 (archivo pdf) en la parte inferior de esta página. Total 30 Páginas | ||
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XTR108
XTR108
SBOS187C – OCTOBER 2001 – REVISED JULY 2005
4-20mA, TWO-WIRE TRANSMITTER
“Smart” Programmable with Signal Conditioning
FEATURES
q COMPLETE TRANSMITTER + RTD
LINEARIZATION
q TWO-WIRE, 4-20mA OUTPUT
q VOLTAGE OUTPUT (0.5V to 4.5V)
q ELIMINATES POTENTIOMETERS AND
TRIMMING
q DIGITALLY CALIBRATED
q 5V SUB-REGULATOR OUTPUT
q SERIAL SPI BUS INTERFACE
q SSOP-24 PACKAGE
APPLICATIONS
q REMOTE RTD TRANSMITTERS
q PRESSURE BRIDGE TRANSMITTERS
q STRAIN GAGE TRANSMITTERS
q SCADA REMOTE DATA ACQUISITION
q WEIGHING SYSTEMS
q INDUSTRIAL PROCESS CONTROL
DESCRIPTION
The XTR108 is a “smart,” programmable, 4-20mA, two-wire
transmitter designed for temperature and bridge sensors.
Zero, span, and linearization errors in the analog signal
path can be calibrated via a standard digital serial interface,
eliminating manual trimming. Non-volatile external EEPROM
stores calibration settings.
The all-analog signal path contains an input multiplexer,
autozeroed programmable-gain instrumentation amplifier, dual
programmable current sources, linearization circuit, voltage
reference, sub-regulator, internal oscillator, control logic, and
an output current amplifier. Programmable level shifting
compensates for sensor DC offsets. Selectable
up- and down-scale output indicates out-of-range and burn-
out per NAMUR NE43. Automatic reset is initiated when
supply is lost.
Current sources, steered through the multiplexer, can be
used to directly excite RTD temperature sensors, pressure
bridges, or other transducers. An uncommitted op amp can
be used to convert current into a voltage. The XTR108 is
specified for –40°C to +85°C.
EEPROM
RTD
V/I-0
V/I-1
V/I-2
V/I-3
V/I-4
V/I-5
R1 R2 R3 R4 R5
Excitation
SPI and
Control Circuits
Linearization
PGA
IO
V/I
XTR108
IRet
VPS
4-20mA
RLOAD
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
SPI is a trademark of Motorola, Inc. All other trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
www.ti.com
Copyright © 2001-2005, Texas Instruments Incorporated
1 page  
PIN CONFIGURATION
Top View
V/I-0 1
V/I-1 2
V/I-2 3
V/I-3 4
V/I-4 5
V/I-5 6
CFILTER 7
RLIN 8
VO 9
IIN 10
IO 11
IRET 12
XTR108
24 OPA +IN
23 OPA –IN
22 OPA OUT
21 REFOUT
20 REFIN
19 RSET
18 CS1
17 SCLK
16 SDIO
15 CS2
14 VGATE
13 VS
SSOP
PIN ASSIGNMENTS
PIN
V/I-0
V/I-1
V/I-2
V/I-3
V/I-4
V/I-5
CFILTER
RLIN
VO
IIN
IO
IRET
VS
VGATE
CS2
SDIO
SCLK
CS1
RSET
REFIN
REFOUT
OPA OUT
OPA –IN
OPA +IN
NAME
MUX Input Channel 0 and/or IREF Out
MUX Input Channel 1 and/or IREF Out
MUX Input Channel 2 and/or IREF Out
MUX Input Channel 3 and/or IREF Out
MUX Input Channel 4 and/or IREF Out
MUX Input Channel 5 and/or IREF Out
Filter Capacitor
Linearization
PGA Output
Current Input
Output Current
Return Current
Voltage Regulator
Gate Voltage
Chip Select 2
Serial Data Input/Output
Serial Clock
Chip Select 1
Resistor for Reference
Voltage Reference Input
Voltage Reference Output
Uncommitted Op Amp Output
Uncommitted Op Amp Negative Input
Uncommitted Op Amp Positive Input
FUNCTION
MUX Input to PGA and/or IREF to Sensor
MUX Input to PGA and/or IREF to Sensor
MUX Input to PGA and/or IREF to Sensor
MUX Input to PGA and/or IREF to Sensor
MUX Input to PGA and/or IREF to Sensor
MUX Input to PGA and/or IREF to Sensor
Filter to Reduce Chopper Noise in Autozeroing PGA
Linearization Range Adjustment Resistor
PGA Amplified Output of Differential Sensor Input
Input to Output Current Amplifier
4-20mA Current for Output Loop
Return for All External Circuitry Current
Supply Voltage for XTR and External Circuitry, If Used
Gate Voltage for External MOSFET Transistor
Select for XTR Serial Port to External EEPROM (Output from XTR Only)
Serial Data Input or Output
Serial Clock
Select for External µC Serial Port (Input to XTR Only)
Sets Current Reference
Voltage Reference Input to XTR
Voltage Reference Output from Internal Bandgap
Uncommitted Op Amp Output
Uncommitted Op Amp Negative Input
Uncommitted Op Amp Positive Input
XTR108
SBOS187C
www.ti.com
5
5 Page 
OVERALL
PROGRAM
VOLTAGE REFERRED TO VO PIN
WITH RESPECT TO IRET
VZERO = VZ PROGRAM + VZ COARSE + VZ FINE
V Z PROGRAM
=
3.5VREF
8
COARSE DAC
V Z COARSE
=
V REF
80
• N13
4
FINE DAC
V Z FINE
=
V REF
80
• N12
64
NOTE: N13 and N12 are assigned decimal values of registers 13 and 12, respectively.
TABLE II. Equations for Calculating Zero Output.
CURRENT REFERRED TO IOUT PIN
IZERO = IZ PROGRAM + IZ COARSE + IZ FINE
IZ PROGRAM
=
175VREF
8R VI
IZ COARSE
=
5VREF
8R VI
• N13
4
IZ FINE
=
5VREF
8R VI
• N12
64
The circuit is designed for compliance with NAMUR NE43
recommendation for sensor interfaces. The limit levels are
listed in Tables VII and VIII. Because of the large step sizes,
units that use this feature should be checked if the value is
critical. The under-scale limit circuit will override the Zero
DAC level if it is set lower and there is not enough sensor
offset at the PGA input.
It may be necessary to disable limiting if the XTR108 is used
in applications other than a 4-20mA transmitter, where the
PGA output is between 0.5V and 4.5V.
SENSOR FAULT DETECTION CIRCUIT
To detect sensor burnout and/or short, a set of four compara-
tors is connected to the inputs of the PGA. If any of the
inputs are taken outside of the PGA’s common-mode range,
the corresponding comparator sets a sensor fault flag that
causes the PGA output to go either to the upper or lower
error limit. The state of the fault condition can be read in the
digital form from register 3. The direction of the analog
output is set according to the “Alarm Configuration Regis-
ter” (see Table X). The level of the output is produced as
follows: if the over-scale/under-scale limiting is enabled, the
error levels are: over-scale limit +2LSBs of the over-scale
DAC, about 1mA referred to IOUT or 0.125V referred to VO,
of under-scale limit –2LSBs of the under-scale DAC, about
0.4mA referred to IOUT or 0.05V referred to VO. If the over-
scale/under-scale limiting is disabled, the PGA output volt-
age will go to within 150mV of either positive or negative
supply (VS or IRET), depending on the alarm configuration
bit corresponding to the error condition.
OUTPUT CURRENT AMPLIFIER + RVI RESISTOR
To produce the 4-20mA output, the XTR108 uses a current
amplifier with a fixed gain of 50A/A. The voltage from the
PGA is converted to current by the external resistor, RVI. Pin
IRET, the common potential of the circuit (substrate and local
ground), is connected to the output and inverting input of the
amplifier. This allows collecting all external and internal
supply currents, sensor return current, and leakage currents
from the different parts of the system and accounting for
them in the output current. The current from RVI flows into
the pin IIN that is connected to the noninverting input and
therefore, is at ground potential as well. The ratio of two
matched internal resistors determines a current gain of this
block. Note that the IOUT pin is always biased below the
substrate potential.
EXCITATION CURRENT DACS AND RSET RESISTOR
Two matched adjustable reference current sources are avail-
able for sensor excitation. The defining equations are given
in Table III. Both current sources are controlled simulta-
neously by the coarse and fine DACs with a pedestal.
The external resistor RSET is used to convert the REF voltage
into the reference current for the sensor excitation DACs.
The total current output of the DACs is split, producing two
references: IREF1 and IREF2. Both of the current references
match very closely over the full adjustment range without
mismatched differential steps. Both current reference out-
puts must be within the compliance range, i.e.: one reference
cannot be floated since it will change the value of the other
current source.
The recommended value of RSET is 12.1kΩ for use with
100Ω RTD sensors. This generates IREF1, 2 = 492µA currents
when both coarse and fine DACs are set to zero. The value
of the RSET resistor can be increased if lower reference
currents are required, i.e.: for 1000Ω RTD or a bridge
sensor.
OVERALL
PROGRAM
COARSE DAC
FINE DAC
REFERENCE CURRENT
IREF1, 2 = IREF PROGRAM + IREF COARSE + IREF FINE
IREF PROGRAM
=
5VREF
R SET
IREF COARSE
=
V REF
R SET
• N11
64
IREF FINE
=
V REF
R SET
• N10
1024
NOTE: N11 and N10 are the decimal values of registers 11 and 10,
respectively.
TABLE III. Equations for Calculating the Values of Each
Reference Current.
Similar to the Zero DACs, the outputs of the fine and coarse
DAC are summed together with the pedestal IREF PROGRAM.
Each of the excitation DACs has 8-bit resolution (256 steps)
with 4-bit overlap between the coarse and the fine. This
XTR108
SBOS187C
www.ti.com
11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet XTR108.PDF ] | |
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