DAC7750IPWPR.B datasheet(27/56 Pages) TI2

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8.4 Device Functional Modes

8.4.1 Setting Current-Output Ranges

The current output range is set according to Table 8-5.

Table 8-5. RANGE Bits vs Output Range

RANGE

OUTPUT RANGE

101

4 mA to 20 mA

110

0 mA to 20 mA

111

0 mA to 24 mA

Note that changing the RANGE bits at any time causes the DAC data register to be cleared.

8.4.2 Current-Setting Resistor

Resistor RSET (used to convert the DAC voltage to current) illustrated in Figure 8-2 determines the stability of the

output current over temperature. If desired, an external, low-drift, precision 15-kΩ resistor can be connected to

the ISET-R pin and used instead of the internal RSET resistor.

8.4.3 BOOST Configuration for IOUT

Figure 8-5 illustrates an external NPN transistor used 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 configuration 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.

The inclusion of the bipolar junction transistor (BJT) adds an additional open loop gain to internal amplifier A2

(see Figure 8-2) and thus, can cause possible instability. Adding series emitter resistor R2 decreases the gain

of the stage created by the BJT and internal R3 resistor (see Figure 8-2) especially for cases where RLOAD is

a short or a very small load, such as a multimeter. Recommended values for R1, R2, and C1 in this circuit are

1 kΩ, 30 Ω and 22 nF, respectively. An equivalent solution is to place R2 (with a recommended value of 3 kΩ

instead of 30 Ω) in series with the base of the transistor instead of the configuration provided in Figure 8-5. Note

that there is some gain error introduced by this configuration; see Figure 7-14, Figure 7-15 and Figure 7-16. Use

the internal transistor in most cases because the values in Section 7.5 are based on the configuration with the

internal on-chip PMOS transistor.

RLOAD

DACx750

BOOST

IOUT

GND

Figure 8-5. Boost Mode Configuration

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DAC7750, DAC8750

SBAS538D – DECEMBER 2013 – REVISED DECEMBER 2021

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