AD5410 Analog Devices, AD5410 Datasheet - Page 23

• Manufacturer Part Number: AD5410
• Description: Single-Channel, 12-/16-Bit, Serial Input, 4 mA to 20 mA, Current Source DAC
• Manufacturer: Analog Devices

Specifications of AD5410

• Resolution (bits): 12bit
• Max Pos Supply (v): +26.4V
• Dac Input Format: SPI

FEEDBACK/MONITORING OF OUTPUT CURRENT
For feedback or monitoring of the output current value, a sense
resistor can be placed in series with the I
voltage drop across it measured. As well as being an additional
component, the resistor increases the compliance voltage
required. An alternative method is to use a resistor that is
already in place. R3 is such a resistor and is internal to the
AD5410/AD5420, as shown in Figure 46. By measuring the
voltage between the R3
output current can be calculated as follows:
where:
V
and BOOST pins
I
value of 444 µA.
R3 is the resistance value of resistor R3 with a typical value of 40 Ω.
Figure 45. Smoothing Out the Steps Caused by the Digital Slew Rate Control
BIAS
R3
is the voltage drop across R3 measured between the R3
is a constant bias current flowing through R3 with a typical
I
OUT
6.8
6.7
6.6
6.5
6.4
6.3
6.2
6.1
–1
=
V
R
Figure 46. Structure of Current Output Circuit
R
0
3
3
−
T
AV
R
A
LOAD
I
I
BIAS
1
DD
BIAS
= 25°C
AV
= 24V
SENSE
= 300Ω
DD
R
R3
40Ω
2
444µA
METAL
and BOOST pins, the value of the
Feature
TIME (ms)
3
4
R3
BOOST
I
OUT
NO EXTERNAL CAPS
10nF ON CAP1
10nF ON CAP2
SENSE
OUT
5
output pin and the
6
7
8
SENSE
Rev. C | Page 23 of 28
(2)
R3 and I
coefficient of 30 ppm/°C. Connecting to R3
AV
that have large temperature coefficients and result in large
errors. See Figure 47 for a plot of R3 vs. ambient temperature
and Figure 48 for a plot of R3 vs. output current.
To eliminate errors due to the tolerances of R3 and I
measurement calibration can be performed as the following
example illustrates:
1.
2.
DD
Progam code 0x1000 and measure I
example, the measured values are
I
V
Program Code 0xF000 and measure I
The measured values this time are
I
V
OUT
OUT
avoids incorporating into R3 internal metal connections
40.98
40.96
40.94
40.92
40.90
40.88
40.86
40.84
40.82
40.80
40.78
42.0
41.8
41.6
41.4
41.2
41.0
40.8
40.6
40.4
40.2
40.0
R3
R3
BIAS
= 79.55446 mV
= 946.39628 mV
= 1.47965 mA
= 22.46754 mA
–40
0
T
R3 = V
A
I
R3 = V
both have a tolerance of ±10% and a temperature
OUT
= 25°C
Figure 47. R3 Resistor Value vs. Temperature
= 12mA
R3
–20
R3
/(I
Figure 48. R3 Resistor Value vs. I
/(12mA + 444µA)
OUT
5
+ 444µA)
AMBIENT TEMPERATURE (°C)
0
10
20
I
OUT
(mA)
40
15
AD5410/AD5420
OUT
OUT
60
SENSE
OUT
and V
and V
20
rather than
80
R3
. In this
BIAS
R3
again.
, a two-
100
25