Datasheet

AD5410/AD5420 Data Sheet
Rev. F | Page 26 of 32
R3 and I
BIAS
both have a tolerance of ±10% and a temperature
coefficient of 30 ppm/°C. Connecting to R3
SENSE
rather than
AV
DD
avoids incorporating into R3 internal metal connections
that have large temperature coefficients and result in large
errors. See Figure 49 for a plot of R3 vs. ambient temperature
and Figure 50 for a plot of R3 vs. output current.
40.98
40.96
40.94
40.92
40.90
40.88
40.86
40.84
40.82
40.80
40.78
–40 –20 0 20 40 60 80 100
AMBIENT TEMPERATURE (°C)
R3 RESISTANCE (Ω)
07027-051
I
OUT
= 12mA
R3 = V
R3
/(12mA + 444µA)
Figure 49. R3 Resistor Value vs. Temperature
42.0
41.8
41.6
41.4
41.2
41.0
40.8
40.6
40.4
40.2
40.0
0 5 10 15 20 25
I
OUT
(mA)
R3 (Ω)
07027-052
T
A
= 25°C
R3 = V
R3
/(I
OUT
+ 444µA)
Figure 50. R3 Resistor Value vs. I
OUT
To eliminate errors due to the tolerances of R3 and I
BIAS
, a two-
measurement calibration can be performed as the following
example illustrates:
1. Program code 0x1000 and measure I
OUT
and V
R3
. In this
example, the measured values are
I
OUT
= 1.47965 mA
V
R3
= 79.55446 mV
2. Program Code 0xF000 and measure I
OUT
and V
R3
again.
The measured values this time are
I
OUT
= 22.46754 mA
V
R3
= 946.39628 mV
Using this information and Equation 2, two simultaneous
equations can be generated from which the values of R3 and
I
BIAS
can be calculated as follows:
OUT
R
BIAS
BIAS
R
OUT
I
R
V
I
I
R
V
I
−=⇒
−=
3
3
3
3
Simultaneous Equation 1
00147965.
0
3
07955446
.0
−
=
R
I
BIAS
Simultaneous Equation 2
02246754.0
3
94639628.0
−=
R
I
BIAS
From these two equations,
302.
413 =R
Ω and
5.446=
BIAS
I
μA
And Equation 2 becomes
µA
V
I
R
OUT
5.446
302.41
3
−=