DAC7760IPWPR datasheet(48/63 Pages) TI1

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OUT

15 V

SET

OUT

GND

AVDD

REFIN

REFOUT

GND

SCLK

LDAC

15 V

-15 V

15 V

-15 V

15 V

-15 V

5 V

DAC7760, DAC8760

SBAS528B – JUNE 2013 – REVISED JUNE 2016

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Typical Application (continued)

9.2.1.2 Detailed Design Procedure

Figure 97. Generic Design for Typical PLC Current and Voltage Outputs

Figure 97 illustrates a common generic solution for realizing these desired voltage and current output spans.

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 voltage output circuit is composed of amplifier A3 and the resistor network consisting of RFB, RG1, and RG2.

A3 operates as a modified summing amplifier, where the DAC controls the noninverting input and the inverting

input has one path to GND and a second to VREF. This configuration allows the single-ended DAC to create both

the unipolar 0-V to 5-V and 0-V to 10-V outputs and the bipolar ±5-V and ±10-V outputs by modifying the values

of RG1 and RG2.

Figure 96 generates clean ±15-V supplies using a synchronous step-down regulator (TPS54062) and two high-

voltage, ultra-low noise, linear regulators (TPS7A49 and TPS7A30). A field supply terminal is shown instead of

the more common use case of a back-plane supply. 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 DACx760 to save components and cost. The

DACx760 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 TIPD153.

9.2.1.3 Application Curves

The current output circuit was measured in 0-mA to 24-mA mode using an 8.5 digit digital multi-meter to measure

the output while driving a 300-

Ω load at 25°C. The measured results are shown in Figure 98. The voltage output

circuit was measured in ±10-V mode using an 8.5 digit digital multi-meter to measure the output while driving a 1-

Ω load at 25°C. The measured results are shown in Figure 99. In both cases, the voltage and current outputs

remain within the specified performance of the data sheet.

DAC7760IPWPR Datasheet(PDF) 48 Page - Texas Instruments

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