AD5421_11 AD [Analog Devices], AD5421_11 Datasheet - Page 31

• Manufacturer Part Number: AD5421_11
• Description: 16-Bit, Serial Input, Loop-Powered, 4 mA to 20 mA DAC
• Manufacturer: AD [Analog Devices]

To determine the absolute worst-case overall error, the reference
and R
maximum error. For example, when using an external reference
and external R
of full-scale range. Assuming that the absolute errors for the
voltage reference and R
0.05% with temperature coefficients of 3 ppm/°C and 2 ppm/°C,
respectively, the overall worst-case error is as follows:
This is the absolute worst-case value when the AD5421 operates
over the temperature range of −40°C to +105°C. An error of this
value is very unlikely to occur because the temperature coeffi-
cients of the individual components do not exhibit the same
drift polarity, and, therefore, an element of cancelation occurs.
For this reason, the TC values should be added in a root of
squares fashion.
A further improvement can be gained by performing a two-point
calibration at zero scale and full scale, thus reducing the absolute
errors of the voltage reference and R
error of 1 LSB or 0.0015% FSR. After performing this calibration,
the total maximum error becomes
Total Error =
To reduce this error value further, a voltage reference and R
resistor with lower TC specifications must be chosen.
THERMAL AND SUPPLY CONSIDERATIONS
The AD5421 is designed to operate at a maximum junction temp-
erature of 125°C. To ensure reliable and specified operation over
the lifetime of the product, it is important that the device not be
operated under conditions that cause the junction temperature
to exceed this value.
Table 24. Thermal and Supply Considerations (External MOSFET Not Connected)
Parameter
Maximum Power
Maximum Ambient
Maximum Supply
. 0
Dissipation
Temperature
Voltage
048
Worst-Case Error =
AD5421 Error + V
R
Worst-Case Error =
0.048% + 0.04% + [(3/10
0.05% + [(2/10
SET
SET
%
errors can be directly summed with the specified AD5421
+
Absolute Error + R
. 0
0015
SET
resistor, the maximum AD5421 error is 0.048%
%
6
+
) × 100 × 145]% = 0.21% FSR
REF
. 0 (
SET
0435
Absolute Error + V
resistor are, respectively, 0.04% and
SET
Description
Maximum permitted power dissipation when operating at an
ambient temperature of 105°C
Maximum permitted ambient temperature when operating from a
supply of 52 V while regulating a loop current of 22.8 mA
Maximum permitted supply voltage when operating at an ambient
temperature of 105°C while regulating a loop current of 22.8 mA
6
) × 100 × 145]% +
%)
TC
2
+
SET
. 0 (
resistor to a combined
029
%)
REF
2
TC +
=
. 0
102
%
FSR
SET
Rev. 0 | Page 31 of 32
Excessive junction temperature can occur if the AD5421
experiences elevated voltages across its terminals while
regulating the loop current at a high value. The resulting
junction temperature depends on the ambient temperature.
Table 24 provides the bounds of operation at maximum ambient
temperature and maximum supply voltage. This information is
displayed graphically in Figure 49 and Figure 50. These figures
assume that the exposed paddle is connected to a copper plane
of approximately 6 cm
Figure 49. Maximum Power Dissipation vs. Ambient Temperature
Figure 50. Maximum Supply Voltage vs. Ambient Temperature
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
60
50
40
30
20
10
0
0
25
25
45
45
2
AMBIENT TEMPERATURE (°C)
AMBIENT TEMPERATURE (°C)
.
28-Lead TSSOP Package
T
125
T
T
I
J
J
J
LOOP
MAX
MAX
MAX
−
θ
JA
×
((
−
−
−
65
65
52
θ
(
T
T
P
JA
A
A
D
×
×
. 0
=
=
θ
0228
. 0
125
JA
125
0228
)
85
85
=
32
)
−
−
×
105
×
105
32
32
)
AD5421
=
=
=
625
87
27
105
105
o
mW
C
V