DAC7750IPWPR.B datasheet(38/56 Pages) TI2

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9.2.2 Detailed Design Procedure

Figure 9-4 illustrates a common generic solution for realizing these desired voltage and current output spans.

IOUT

15V

RSET

GND

AVDD

VREFIN/VREFOUT

GND

DIN

SCLK

LDAC

15V

-15V

15V

-15V

Figure 9-4. Generic Design for Typical PLC Current and Voltage Outputs

The current output circuit is comprised of amplifiers A1 and A2, MOSFETs Q1 and Q1, and the three resistors

RSET, RA, and RB. This two-stage current source enables the ground-referenced DAC output voltage to drive the

high-side amplifier required for the current-source.

The high-level of integration of the DACx750 family lends itself very well to the design of analog output modules,

offering simplicity of design and reducing solution size. The DACx750 integrates all of the components shown in

Figure 9-4 allowing a software configurable current output driver. Figure 9-3 illustrates an example circuit design

for such an application using the DACx750 for the current output driver.

The design uses two triple channel isolators (ISO7631FC) to provide galvanic isolation for the digital lines to

communicate to the main controller. Note that these isolators can be driven by the internally-generated supply

(DVDD) from the DACx750 to save components and cost. The DACx750 supplies up to 10 mA that meets the

supply requirements of the two isolators running at up to 10 Mbps. Note that additional cost savings are possible

if noncritical digital signals such as CLR and ALARM are tied to GND or left unconnected. Finally, a protection

scheme with transient voltage suppressors and other components is placed on all pins which connect to the

field.

The protection circuitry is designed to provide immunity to the IEC61000-4 test suite which includes system-level

industrial transient tests. The protection circuit includes transient voltage suppressor (TVS) diodes, clamp-to-rail

steering diodes, and pass elements in the form of resistors and ferrite beads. For more detail about selecting

these components, see the Single-Channel Industrial Voltage and Current Output Driver, Isolated, EMC/EMI

Tested Reference Design.

DAC7750, DAC8750

SBAS538D – DECEMBER 2013 – REVISED DECEMBER 2021

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DAC7750IPWPR.B Datasheet(PDF) 38 Page - Texas Instruments