Datasheet

ManualsBrandsTEXAS INSTRUMENTS ManualsData collecting ICsData acquisition IC - DA converter (DAC) VQFN 24

ANALOG OUTPUT

LoadDACRegisters

SerialDataIn

Clock

SerialDataOut

0.1 Fm 1 Fm

+5V

ExternalReference

+5.0000V

OUT

1.8Vto5V

ResetDACRegisters

SDOSEL

Chip-Select

SCLK

SDI

LDAC

AGND

V -S

REFL

(ThermalPad)

PDN

RST

USB/BTC

GAIN

RSTSEL

DAC9881

IOV

SDO

DGND

SDOSEL

V -S

REFH

OUT

-F

REF

V -F

REFH

0.1 Fm 1 Fm

DAC9881

SBAS438A – MAY 2008 – REVISED AUGUST 2008 .........................................................................................................................................................

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The DAC9881 offers a force and sense output configuration for the high open-loop gain output amplifier. This

feature allows the loop around the output amplifier to be closed at the load (as shown in Figure 66 ), thus

ensuring an accurate output voltage. The output buffer V

OUT

and R

pins are provided so that the output op amp

buffer feedback can be connected at the load. Without a driven load, the DAC9881 output typically swings to

within 15mV of the AGND and AV

supply rails. Because of the high accuracy of these DACs, system design

problems such as grounding and wiring resistance become very important. A 18-bit converter with a 5V full-scale

range has an LSB value of 19 µ V. The DAC9881 has a typical feedback resistor current of 0.5mA; thus, a series

wiring resistance of only 100m Ω (R

) causes a voltage drop of 50 µ V. In terms of a system layout, the resistivity

of a typical 1-ounce copper-clad printed circuit board (PCB) is 0.5m Ω per square. For a 0.5mA current, a

0.25mm wide printed circuit conductor 25mm long results in a voltage drop of 25 µ V. Note that the wiring

resistance of R

is not critical as long as the feedback resistor (R

) is connected at the driven load.

Figure 66. Analog Output Closed-Loop Configuration

and R

represent wiring resistance)

Product Folder Link(s): DAC9881