AD5421 Analog Devices, AD5421 Datasheet - Page 32

• Manufacturer Part Number: AD5421
• Description: 16-Bit, Serial Input, Loop-Powered, 4mA to 20mA DAC
• Manufacturer: Analog Devices

Specifications of AD5421

• Resolution (bits): 16bit
• Dac Settling Time: 50µs
• Max Pos Supply (v): +52V
• Single-supply: Yes
• Dac Type: Current Out
• Dac Input Format: SPI

AD5421
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
Maximum
Maximum
. 0
Power
Dissipation
Ambient
Temperature
Supply
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%
%
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]% = 0.21% FSR
REF
. 0 (
SET
0435
resistor are, respectively, 0.04% and
Absolute Error + V
SET
6
) × 100 × 145]% +
%)
TC
2
+
SET
. 0 (
resistor to a combined
029
%)
REF
2
TC +
=
. 0
102
%
FSR
SET
32-Lead LFCSP
125
Rev. C | Page 32 of 36
T
T
J
J
MAX
MAX
T
I
J
LOOP
θ
−
MAX
JA
(
(
−
−
52
P
T
×
−
D
×
A
θ
T
×
JA
. 0
=
A
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 50 and Figure 51. These figures
assume that the exposed paddle is connected to a copper plane
of approximately 6 cm
θ
0228
125
=
JA
. 0
=
125
40
Figure 50. Maximum Power Dissipation vs. Ambient Temperature
−
0228
)
Figure 51. Maximum Supply Voltage vs. Ambient Temperature
×
105
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
60
50
40
30
20
10
40
−
0
0
40
0
105
×
)
=
=
40
500
77
=
°
50
C
mW
21
20
LFCSP
TSSOP
V
2
AMBIENT TEMPERATURE (°C)
AMBIENT TEMPERATURE (°C)
.
60
28-Lead TSSOP
125
T
T
T
I
40
J
J MAX
J
LOOP
MAX
MAX
θ
−
70
JA
×
LFCSP
−
((
TSSOP
−
−
θ
52
(
T
T
60
P
JA
A
A
D
×
80
=
×
=
. 0
θ
125
0228
. 0
JA
125
0228
)
80
=
32
90
−
Data Sheet
)
−
105
×
105
×
32
32
)
100
100
=
=
=
625
87
27
°
mW
C
V