DAC8750IPWPR datasheet(27/53 Pages) TI1

27 / 53 page

RLOAD

DACx750

BOOST

IOUT

GND

DAC7750, DAC8750

www.ti.com

SBAS538B – DECEMBER 2013 – REVISED JUNE 2016

Product Folder Links: DAC7750 DAC8750

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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 5.

Table 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) shown in Figure 53 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 terminal and used instead of the internal RSET resistor.

8.4.3 BOOST Configuration for IOUT

Figure 56 shows 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 53) 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 53) 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 shown in Figure 56. Note that there is

some gain error introduced by this configuration, as seen in Figure 15, Figure 16 and Figure 17. Use the internal

transistor in most cases because the values in Electrical Characteristics are based on the configuration with the

internal on-chip PMOS transistor.

Figure 56. Boost Mode Configuration

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