DAC7760IPWPR datasheet(36/63 Pages) TI1

36 / 63 page

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

RLOAD

DACx760

BOOST

IOUT

GND

DAC7760, DAC8760

SBAS528B – JUNE 2013 – REVISED JUNE 2016

www.ti.com

Product Folder Links: DAC7760 DAC8760

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8.4.2 Boost Configuration for IOUT

An external NPN transistor can be used as shown in Figure 87 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 87. Note that there is some gain error introduced by

this configuration as seen in Figure 47 for the 0-mA to 24-mA range. TI recommends using the internal transistor

in most cases as the values in the Electrical Characteristics are based on the configuration with the internal on-

chip PMOS transitor.

Figure 87. 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 93. 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 88. However, note that power supply ripple

also couples into the part through these capacitors.

Figure 88. IOUT vs Time for Different Capacitor Values on CAP1 and CAP2

8.4.4 HART Interface

On the DACx760, HART digital communication can be modulated onto the input signal by two methods:

DAC7760IPWPR Datasheet(PDF) 36 Page - Texas Instruments

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