DAC8550_16 Datasheet, PDF (20/31 Pages) Texas Instruments – 16-bit, Ultra-Low Glitch, Voltage Output Digital-To-Analog Converter

DAC8550
SLAS476F – MARCH 2006 – REVISED MARCH 2016
8.2 Typical Applications
8.2.1 Loop-Powered 2-Wire 4-mA to 20-mA Transmitter With XTR116
C2 || C3
0.1001 µF
U1
V+
Vref
DAC8550
R1
102.4 NŸ
VOUT
C1
2.2 µF
R2
49.9 Ÿ
R3
25.6 NŸ
VREG
Vref
XTR116
Reference
Regulator
V+
IIN
+
U2
±
IRET
2475 Ÿ
25 Ÿ
RLIM
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V+
V+
B
Q1
Q1
E
IO
Return
Figure 52. Loop-Powered Transmitter
8.2.1.1 Design Requirements
This design is commonly referred to as a loop-powered, or 2-wire, 4-mA to 20-mA transmitter. The transmitter
has only two external input terminals: a supply connection and an output, or return, connection. The transmitter
communicates back to its host, typically a PLC analog input module, by precisely controlling the magnitude of its
return current. In order to conform to the 4-mA to 20-mA communication standard, the complete transmitter must
consume less than 4 mA of current. The DAC8550 enables the accurate control of the loop-current from 4 mA to
20 mA in 16-bit steps.
8.2.1.2 Detailed Design Procedure
Although it is possible to recreate the loop-powered circuit using discrete components, the XTR116 provides
simplicity and improved performance due to the matched internal resistors. The output current can be modified if
necessary by looking using Equation 4.
I_OUT (Code)
=
æ
ç
çè
V_ref ´ Code
2^N ´R₃
+
V_REG
R₁
ö
÷
÷ø
´
æç₁₊
è
2475 W
25 W
ö
÷
ø
(4)
For more details of this application, see 2-wire, 4-mA to 20-mA Transmitter, EMC/EMI Tested Reference Design
(TIDUAO7). It covers in detail the design of this circuit as well as how to protect it from EMC/EMI tests.
8.2.1.3 Application Curves
Total unadjusted error (TUE) is a good estimate for the performance of the output as shown in Figure 53. The
linearity of the output or INL is in Figure 54.
20
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