DAC7750IPWPR.B datasheet(28/56 Pages) TI2

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8.4.4 Filtering The Current Output

The DACx750 provides access to internal nodes of the circuit; see Figure 9-2. Place capacitors on these pins

and AVDD to form a filter on the output current, reducing bandwidth and the slew rate of the output, especially

useful for driving inductive loads. However, to achieve large reductions in slew rate, use the programmable slew

rate to avoid having to use large capacitors. Even in that case, use the capacitors on CAP1 and CAP2 to smooth

out the stairsteps caused by the digital code changes as shown in Figure 8-6. However, note that power supply

ripple also couples into the devices through these capacitors.

Time (200 µs/div)

no cap

3 nF CAP1

3 nF CAP2

10 nF CAP1

10 nF CAP2

C001

A = 25ºC

AVDD = 24 V

LOAD = 250 Ÿ

Figure 8-6. IOUT vs Time for Different Cap Values on CAP1 and CAP2

8.4.5 Output Current Monitoring

Many applications, especially for functional safety, require monitoring to make sure that the output current

stays close to the programmed value. To monitor the output current, place a sense resistor in series with the

output and measure the voltage across the resistor. However, this resistor reduces the compliance voltage

available for the load. The DACx750 provide access to an internal precision resistor (R3 in Figure 8-2) through

the R3-SENSE and BOOST pins to perform analog readback for monitoring the output current. Measure the

voltage between the R3-SENSE and BOOST pins and divide by the value of the R3 resistor to determine the

magnitude of the output current. The R3 resistor has a typical value of 40 Ω (see Figure 7-38 for a plot of

resistance vs temperature) with a temperature drift coefficient of 40 ppm/°C (see Figure 7-39 for a histogram of

R3 resistance temperature drift). The R3 resistor is tested to stay within the minimum (36 Ω) and maximum (44

Ω) resistance values shown in the R3 Resistor portion of Section 7.5. To remove the tolerance error, perform a

simple calibration by programming a certain value of output current, measuring the voltage across R3-SENSE

and BOOST, and calculating the exact value of R3.

DAC7750, DAC8750

SBAS538D – DECEMBER 2013 – REVISED DECEMBER 2021

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DAC7750IPWPR.B Datasheet(PDF) 28 Page - Texas Instruments