103kW

+5V

Reference

+V

-2.5V

VREF

RREF

AVSS

Power-down

Switch

Current

used to

set Full-Scale

0.1 F

m

(1)

117kW

R

30k

REF

W

DAC1280

www.ti.com

SBAS432A – APRIL 2010 – REVISED SEPTEMBER 2010

Table 1. DAC1280 Ideal Output Scaling(1)

TDATA 1s DENSITY (%)

IOUTP – IOUTN (mA)

VP – VN (V)

25

–1250

● Gain

–2.5

● Gain

37.5

–625

● Gain

–1.25

● Gain

50

0

0

62.5

+625

● Gain

+1.25

● Gain

75

+1250

● Gain

+2.5

● Gain

(1)

VREF = 5V, RREF = 30kΩ, external current-to-voltage converter resistors = 2kΩ. Output current and

voltage are differential. Excludes the effects of DAC1280 offset, gain and linearity errors, errors in

reference voltage, errors as a result of external resistors, and errors from the external

current-to-voltage conversion. Refer to Figure 27.

VREF Reference Voltage Input

RREF Reference Resistor

The DAC1280 requires an external reference for

A 30k

Ω resistor, connected from VREF to AVSS, is

operation. The reference voltage of the DAC1280 is

required for operation. This resistor, in combination

defined as the voltage difference between VREF and

with VREF, is used to set the DAC full-scale output.

AVSS (that is, VREF = VREF – AVSS). The DAC1280

The resistor can be used to fine-trim the DAC gain by

output directly scales with VREF; consequently, noise

changing the value from the nominal 30k

Ω. See the

or drift on the reference appear at the DAC1280

Output Scaling section for more information.

output. A low-drift and low-noise precision reference

The external resistor accuracy and temperature drift

is recommended for best performance.

directly affect the DAC1280 output accuracy. A

For best layout, connect the ground pin of the

low-drift, precision resistor is recommended for best

external reference directly to the AVSS terminal to

performance. Connect the resistor directly to the

minimize possible crosstalk. A recommended 0.1mF

RREF and AVSS pins using short and direct traces.

ceramic capacitor connected directly across VREF

Keep RREF stray capacitance to a minimum. Refer to

and AVSS reduces noise susceptibility.

Figure 29 for the reference input connection.

Figure 29 shows the reference input voltage and

reference resistor connection to the DAC1280. The

DAC1280 loads VREF with 220k

Ω. The 220kΩ

resistor disconnects in power-down mode.

(1)

Recommended noise capacitor.

Figure 29. Reference Input Connection

Copyright © 2010, Texas Instruments Incorporated

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