參數(shù)資料
型號(hào)： XTR108
英文描述： 4-20mA, TWO-WIRE TRANSMITTER Smart Programmable with Signal Conditioning
中文描述： 的4 - 20mA，兩線制變送器可編程智能與信號(hào)調(diào)理
文件頁數(shù)： 11/27頁
文件大?。?/td> 497K
代理商： XTR108
XTR108
SBOS187B
11
www.ti.com
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 I
OUT
or 0.125V referred to V
O
,
of under-scale limit –2LSBs of the under-scale DAC, about
0.4mA referred to I
OUT
or 0.05V referred to V
O
. 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 (V
S
or I
RET
), depending on the alarm configuration
bit corresponding to the error condition.
OUTPUT CURRENT AMPLIFIER + R
VI
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, R
VI
. Pin
I
RET
, 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 R
VI
flows into
the pin I
IN
that is connected to the noninverting input and
therefore, is at ground potential as well. The ratio of two
VOLTAGE REFERRED TO V
O
PIN
WITH RESPECT TO I
RET
CURRENT REFERRED TO I
OUT
PIN
OVERALL
V
ZERO
= V
Z PROGRAM
+ V
Z COARSE
+ V
Z FINE
I
ZERO
= I
Z PROGRAM
+ I
Z COARSE
+ I
Z FINE
=
175
PROGRAM
V
V
8
ZPROGRAM
REF
=
3 5
.
I
V
R
ZPROGRAM
REF
VI
8
COARSE DAC
V
V
N
Z COARSE
REF
80
=
4
13
I
V
R
8
N
Z COARSE
REF
VI
=
5
4
13
FINE DAC
V
V
N
64
ZFINE
REF
80
=
12
I
V
R
8
N
64
ZFINE
REF
VI
=
5
12
NOTE: N
13
and N
12
are assigned decimal values of registers 13 and 12, respectively.
TABLE II. Equations for Calculating Zero Output.
REFERENCE CURRENT
OVERALL
I
REF1, 2
= I
REF PROGRAM
+ I
REF COARSE
+ I
REF FINE
PROGRAM
I
V
R
REFPROGRAM
REF
SET
=
5
COARSE DAC
I
V
R
N
64
REF COARSE
REF
SET
=
11
FINE DAC
I
V
R
N
1024
REFFINE
REF
SET
=
10
NOTE: N
and N
10
are the decimal values of registers 11 and 10,
respectively.
TABLE III. Equations for Calculating the Values of Each
Reference Current.
matched internal resistors determines a current gain of this
block. Note that the I
OUT
pin is always biased below the
substrate potential.
EXCITATION CURRENT DACS AND R
SET
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 R
SET
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: I
REF1
and I
REF2
. 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 R
SET
is 12.1k
for use with
100
RTD sensors. This generates I
REF1, 2
= 492
μ
A currents
when both coarse and fine DACs are set to zero. The value
of the R
SET
resistor can be increased if lower reference
currents are required, i.e.: for 1000
RTD or a bridge
sensor.
Similar to the Zero DACs, the outputs of the fine and coarse
DAC are summed together with the pedestal I
REF PROGRAM
.
Each of the excitation DACs has 8-bit resolution (256 steps)
with 4-bit overlap between the coarse and the fine. This
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
XTR108_12 制造商:BB 制造商全稱:BB 功能描述:4-20mA, TWO-WIRE TRANSMITTER a??Smarta?? Programmable with Signal Conditioning
XTR108-DIE 制造商:TI 制造商全稱:Texas Instruments 功能描述:TWO-WIRE TRANSMITTER
XTR108EA 功能描述:接口 - 專用 4-20mA 2Wire Trsmtr ’Smart’ Prog RoHS:否 制造商:Texas Instruments 產(chǎn)品類型:1080p60 Image Sensor Receiver 工作電源電壓:1.8 V 電源電流:89 mA 最大功率耗散: 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:BGA-59
XTR108EA/2K5 功能描述:接口 - 專用 4-20mA 2Wire Trsmtr ’Smart’ Prog RoHS:否 制造商:Texas Instruments 產(chǎn)品類型:1080p60 Image Sensor Receiver 工作電源電壓:1.8 V 電源電流:89 mA 最大功率耗散: 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:BGA-59
XTR108EA/2K5G4 功能描述:接口 - 專用 4-20mA 2Wire Trsmtr ’Smart’ Prog RoHS:否 制造商:Texas Instruments 產(chǎn)品類型:1080p60 Image Sensor Receiver 工作電源電壓:1.8 V 電源電流:89 mA 最大功率耗散: 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:BGA-59
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