DAC1282_15 Datasheet, PDF (21/46 Pages) Texas Instruments – Low Distortion Digital-to-Analog Converter for Seismic

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DAC1282, DAC1282A
SBAS490B – DECEMBER 2011 – REVISED MAY 2015
8.2.3 Reference Voltage (V_REF)
The DAC1282 requires an external reference for operation. Although reference voltage as low as 2.5 V can be
used, best SNR is achieved with a 5-V reference. The reference input is defined as the voltage difference
between VREF and AVSS (that is, V_REF = VREF – AVSS). The DAC1282 output scales with V_REF; consequently,
reference noise or drift appears on the DAC output. Excessive reference noise may lead to degraded SNR. A
low-drift and low-noise reference is recommended.
Connect the external reference ground pin directly to the AVSS pins using a star connector to AVSS pin 14. Star
connection minimizes the possibility of power-supply crosstalk. Also, connect a 0.1-µF capacitor close to the
VREF and AVSS terminals to reduce noise susceptibility. Figure 35 shows the reference connection. The
reference input impedance is 220 kΩ. In power-down the switch is off, resulting in very high input impedance. For
single-supply applications, connect AVSS to a clean analog ground point.
+V
5V
Reference
VREF
0.1 µF ⁽¹⁾
220 kΩ
Internal
Circuitry
Power-down
Switch
-2.5 V
(1) Recommended bypass capacitor.
AVSS (14)
AVSS (23)
Figure 35. Reference Input Connection
8.2.4 Output Filter (CAPP, CAPN)
The CAPP and CAPN pins are the connections for two external capacitors, one capacitor connects to CAPP and
VOUTP and the other capacitor connects to CAPN and VOUTN. The capacitors are required to filter the DAC
sampling noise. The capacitor values are 1 nF; capacitors with low voltage coefficients should be used (C0G
ceramic or film).
As seen in Figure 36, the external capacitors form an analog low-pass filter with the internal feedback resistors.
After step changes to the data in the sine, dc, and digital data modes, the settling of the DAC and the analog
filter is 100-µs typical, as shown in Figure 46. In pulse mode, the filter is internally disabled, yielding shorter
settling time.
Current
DAC
2k
Output
Amplifier
CAPP
VOUTP
1 nF
VOUTN
2k
1 nF
CAPN
Figure 36. Output Filter
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