DAC8551-Q1 Datasheet, PDF (16/28 Pages) Texas Instruments – Automotive 16-Bit, Ultralow-Glitch, Voltage-Output DAC

DAC8551-Q1
SLASEB8A – FEBRUARY 2016 – REVISED MARCH 2016
8 Application and Implementation
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NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
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+
V_ref
DAC8551-Q1 ^V_OUT
R₁
102.4 kΩ
R3
25.6 kΩ
V_REG ^XTR116
Regulator
C₁
2.2 µF
R₂
49.9 W
V_ref
I_IN
Reference
V+
+
U2
I_RET
2475 Ω
R_LIM
25 Ω
V+
V+
B
Q1
Q1
E
I_O
Return
Figure 32. 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 DAC8551-Q1 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 2.
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
(2)
For more details of this application, see 2-wire, 4-20mA 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.
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