Datasheet

I
LOOP
(mA)
DACCODE (hex)
full accuracy range
24.0
21.5
20.0
4.0
3.5
0.4
0.2
0000 0222 2500
2AAA
D555
E500
FFFF
0444
Programmable I
ERROR
Programmable I
ERROR
MIN(I
LOOP
) ± Loop Powered
MIN(I
LOOP
) ± Self Powered
DAC
-+
I
DAC
I
AUX
I
LOOP
LOOP+
LOOP-
R
1
= 80k
+
-
I
D
I
A
BASE
OUT
COMA
DAC161P997
VD
VA
V
LOCAL
+
-
I
E
R
2
= 40
I
2
R
E
DAC161P997
SNAS515E –JULY 2011–REVISED OCTOBER 2013 www.ti.com
Figure 14. Self-Powered Transmitter
DC Input-Output Transfer Function
The output current sourced by the OUT pin of the device is expressed by:
(2)
The valid DACCODE range is the full 16-bit code space (0x0000 to 0xFFFF), which results in the I
DAC
range of 0
to approximately 12 μA. This, however, does not result in the I
LOOP
range of 0 to 24 mA.
The maximum output current sourced out of OUT pin, I
LOOP
, is 24 mA. The minimum output current is dependent
on the system implementation. The minimum output current is the sum of supply currents of the DAC161P997
internal blocks, I
A
, I
D
, and companion devices present in the system, I
AUX
. The last component current I
E
can
theoretically be controlled down to 0 but, due to the stability considerations of the control loop, it is advised not to
allow the I
E
to drop below 200 μA.
The graph in Figure 15 shows the DC transfer characteristic of the 4 - 20 mA transmitter, including minimum
current limits. The minimum current limit for the Loop-Powered Transmitter is typically around 400 μA
(I
D
+I
A
+I
AUX
+I
E
). The minimum current limit for the Self-Powered Transmitter is typically around 200 μA (I
E
).
Typical values for I
D
and I
A
are listed in the ELECTRICAL CHARACTERISTICS table. I
E
depends on the BJT
device used.
Figure 15. DAC DC Transfer Function
14 Submit Documentation Feedback Copyright © 2011–2013, Texas Instruments Incorporated
Product Folder Links: DAC161P997