DAC161P997_15 Datasheet, PDF (21/39 Pages) Texas Instruments – DAC161P997 Single-Wire 16-bit DAC for 4- to 20-mA Loops

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Application Information (continued)
VD
DAC161P997
SNAS515G – JULY 2011 – REVISED DECEMBER 2014
LOOP+
VA
+
-
V_LOCAL
I_AUX
DAC
I_D
I_DAC
+
BASE
-
I_A
I_LOOP
I_E
RE
COMA
R₁ = 80k
R₂ = 40
I₂
DAC161P997
OUT
Figure 22. Self-Powered Transmitter
8.1.1.1.1 DC Input-Output Transfer Function
The output current sourced by the OUT pin of the device is expressed by:
LOOP-
(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 23 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 Electrical Characteristics. I_E depends on the BJT device used.
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