DAC7760IPWPR datasheet(38/69 Pages) TI2

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8.4.2 Boost Configuration for IOUT

An external NPN transistor can be used as shown in Figure 8-6 to reduce power dissipation on the die. Most

of the load current flows through the NPN transistor with a small amount flowing through the on-chip PMOS

transistor based on the gain of the NPN transistor. This reduces the temperature induced drift on the die and

internal reference and is an option for use cases at the extreme end of the supply, load current, and ambient

temperature ranges. Resistor R2 stabilizes this circuit for cases where the RLOAD is a short or a very small

load like a multimeter. Recommended values for R1, R2 and C1 in this circuit are 1 kΩ, 20 Ω and 0.22 µF. An

equivalent solution is to place R2 (with a recommended value of 2 kΩ instead of the 20 Ω) in series with the base

of the transistor instead of the configuration shown in Figure 8-6. Note that there is some gain error introduced

by this configuration as seen in Figure 7-46 for the 0-mA to 24-mA range. TI recommends using the internal

transistor in most cases as the values in Section 7.5 are based on the configuration with the internal on-chip

PMOS transitor.

RLOAD

DACx760

BOOST

IOUT

GND

Figure 8-6. Boost Mode Configuration

8.4.3 Filtering the Current Output (only on the VQFN package)

The VQFN package provides access to internal nodes of the circuit as shown in Figure 9-3. Capacitors can be

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

the output. However, to achieve large reductions in slew rate, the programmable slew rate can be used to avoid

having to use large capacitors. Even in that case, the capacitors on CAP1 and CAP2 can be used to smooth

out the stairsteps caused by the digital code changes as shown in Figure 8-7. However, note that power supply

ripple also couples into the part 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 8-7. IOUT vs Time for Different Capacitor Values on CAP1 and CAP2

DAC7760, DAC8760

SBAS528D – JUNE 2013 – REVISED DECEMBER 2021

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DAC7760IPWPR Datasheet(PDF) 38 Page - Texas Instruments