Datasheet

Data Sheet AD5421
Rev. G | Page 27 of 36
DAC REGISTER
The DAC register is a read/write register and is addressed
as described in Table 12. The data programmed to the DAC
register determines the loop current, as shown in the Ideal
Output Transfer Function section and in Table 16.
Ideal Output Transfer Function
The transfer function describing the relationship between the
data programmed to the DAC register and the loop current is
expressed by the following three equations.
For the 4 mA to 20 mA output range, the loop current can be
expressed as follows:
mA
4
2
mA16
16
D I
LOOP
+
×








=
For the 3.8 mA to 21 mA output range, the loop current can be
expressed as follows:
mA8
.
3
2
mA
2
.17
16
D I
LOOP
+
×








=
For the 3.2 mA to 24 mA output range, the loop current can be
expressed as follows:
mA
2
.3
2
mA8
.20
16
D I
LOOP
+
×








=
where D is the decimal value of the DAC register.
Table 15. DAC Register Bit Map
MSB LSB
D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
16-bit data
Table 16. Relationship of DAC Register Code to Ideal Loop Current (Gain = 65,536; Offset = 0)
DAC Register Code
Ideal Loop Current (mA)
4 mA to 20 mA Range 3.8 mA to 21 mA Range 3.2 mA to 24 mA Range
0x0000 4 3.8 3.2
0x0001 4.00024 3.80026 3.2003
… … … …
0x7FFF 11.9997 12.39974 13.5997
0x8000 12 12.4 13.6
… … … …
0xFFFE 19.9995 20.99947 23.9994
0xFFFF 19.9997 20.99974 23.9997