Datasheet
103kW
+5V
Reference
+V
-2.5V
VREF
RREF
AVSS
Power-down
Switch
Current
used to
set Full-Scale
0.1 Fm
(1)
117kW
R
30k
REF
W
DAC1280
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SBAS432A –APRIL 2010–REVISED SEPTEMBER 2010
Table 1. DAC1280 Ideal Output Scaling
(1)
TDATA 1s DENSITY (%) IOUTP – IOUTN (mA) V
P
– V
N
(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) V
REF
= 5V, R
REF
= 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 30kΩ 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, V
REF
= VREF – AVSS). The DAC1280 The resistor can be used to fine-trim the DAC gain by
output directly scales with V
REF
; consequently, noise changing the value from the nominal 30kΩ. 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 220kΩ. The 220kΩ
resistor disconnects in power-down mode.
(1) Recommended noise capacitor.
Figure 29. Reference Input Connection
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