XTR108EA-2K5 BURR-BROWN [Burr-Brown Corporation], XTR108EA-2K5 Datasheet - Page 19

• Manufacturer Part Number: XTR108EA-2K5
• Manufacturer: BURR-BROWN [Burr-Brown Corporation]

RTD APPLICATION
The values to be entered into the DAC control registers are
given by the formulas in Table XV.
TABLE XV. Equations for DAC Code Calculation.
This procedure allows calculation of the parameters needed
to calculate the DAC codes for an RTD sensors application.
TABLE XVI. Standard RTD Descriptive Equations.
XTR108
FIGURE 8. Reverse Voltage and Over-Voltage Protection.
SBOS187C
EXCITATION CURRENT I
Coarse DAC code
Fine DAC Code
ZERO OUTPUT I
Coarse DAC Code
Fine DAC Code
LINEARIZATION COEFFICIENT G
Lin DAC Code
R
R
B
R
S
A
C
t
t
O
tan
3 9083
R
R
dard RTD Polynomials
5 775
.
4 183
base RTD value at
.
.
O
O
1
1
e
e
e
At B
At B
N
N
7
12
3
10
12
ZERO
1
1
I
2
2
RET
round
N
round
N
XTR108
for
12
11
13
C t
N
0
0
14
REF
round
round
C
C
1024
:
512
100
100
round
V+
5
t
I
14
13
O
10
C t
V
11
I
64
I
REF
ZERO
V
REF
32
850
LIN
REF
3
or k
5
16
R
I
V
for
1
I
R
REF
C
ZERO
REF
SET
V
VI
REF
G
R
LIN
200
SET
R
2240 16
5120 16
VI
R
0.01 F
LIN
C
140
320
t
0
N
N
C
13
11
D
1
(1)
The diode bridge causes
a 1.4V loss in loop supply
voltage.
1N4148
Diodes
www.ti.com
1) For a chosen temperature range, using an industry-stan-
2) Calculate a relative nonlinearity B
3) Pick an external zero resistor, R
4) Calculate the linearization coefficient::
5) Choose the output zero and full-scale level values, for
G
dard polynomial set as shown in Table XVI, calculate
RTD values at min, max, and the middle temperatures:
ues from above:
ing R
must be corrected by the PGA zero adjustment.
If the value of G
R
G
MAX
the DAC quantization errors. For 100
the required linearization coefficients are in the range
from 0.3 to 0.6 mA/V (1/k ) for all measurement
ranges. Therefore an external R
good setting the full-scale G
1k RTD’s the R
ally.
LIN
instance: I
LIN
LIN
, the R
) the external resistor R
Z
is significantly smaller (> 10 times) than G
greater than R
0 5
NOTE: (1) Zener Diode 36V: 1N4753A or General
Semiconductor Transorb
voltage zener diodes with loop power supply
voltages less than 30V for increased protection.
See “Over-Voltage Surge Protection.”
R
.
L
LIN
B
OUT MIN
V
B
value should be increased to minimize
R
V
MIN
R
LIN
LIN
R
MID
,
MAX
= 4mA, I
V
R
MIN
should be increased proportion-
is larger than G
PS
R
MAX
MAX
–
–
will cause a voltage offset that
Maximum V
less
voltage rating of zener
diode.
R
,
TM
0 5
LIN
MAX
2
LIN MAX
and R
. –
–
B
OUT MAX
1N6286A. Use lower
than
R
V
LIN
Z
has to be changed. If
2
MIN
closest to R
B
PS
V
value of 15.8k is
MID
V
minimum
R
must be
using the RTD val-
~ = 1mA/V. For
MIN
R
= 20mA.
LIN MAX
MIN
RTD sensors
–
MIN
2
= (16/
B R
. Select-
V
LIN
Z
19