DAC1280_15 Datasheet, PDF (15/24 Pages) Texas Instruments – Low Distortion Digital-to-Analog Converter for Seismic Monitoring

DAC1280
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Power Supplies
The DAC1280 has two power supplies, analog and
digital. The analog supply is 5V and can be
configured for bipolar operation (with AVDD = 2.5V
and AVSS = –2.5V), or configured for unipolar
operation (with AVDD = 5V and AVSS grounded).
The common-mode voltage of the external I/V
converter is normally set to the DAC1280 midsupply.
Because AVSS is shared with the reference low
terminal, and the analog supply pins draw
signal-dependent current, the external reference
ground terminal should connect to AVSS using a star
connection close to the DAC. This approach helps to
minimize power-supply coupling to the reference
input.
DVDD is the digital supply and operates over the
range of 1.65V to 3.6V. Bypass the DVDD as well as
the analog supplies with a capacitor (minimum 1mF).
The power supplies can be sequenced in any order.
At power-on, the latter occurrence of DVDD
exceeding 1V, or (AVDD – AVSS) exceeding 3V,
causes an internal power-on reset (POR) to occur. A
POR resets the output to zero. After reset, the first
sampling of TDATA by the DAC1280 occurs on the
sixth CLK rising edge, as Figure 30 shows.
DVDD
AVDD-AVSS
Internal POR
TDATA
CLK
1V
3V
First TDATA Sample
1
2
3
4
5
6
Figure 30. Power-On Sequence
Power Consumption
The total power consumption is the power consumed
by the DAC1280 plus that of the external
current-to-voltage converter. The power consumption
of the DAC1280, in turn, depends on the gain setting.
Table 3 summarizes the DAC1280 power
consumption.
SBAS432A – APRIL 2010 – REVISED SEPTEMBER 2010
Table 3. DAC1280 Power Consumption
GAIN
1/1
1/2
1/4
1/8
1/16
1/32
1/64
DAC1280 POWER (mW)
18
9.6
5.3
3.1
2.1
1.5
1.2
Offset and Gain Error
The DAC1280 features low offset error (±50ppmFS,
typical) and low gain error (±0.02%, gain = 1/1,
typical). Gain match is specified as the maximum
error of gain = 1/1 relative to gains 1/2 to 1/64 of a
single device. Typical gain match error is ±0.1%.
Offset and gain drift are also very low for the
DAC1280. Drift is calculated using the box calculation
method:
Max - Min
Drift calculation: _{Temp Range}
(ppm/°C)
(2)
Where Max and Min are respectively the maximum
and minimum offset or gain errors (in ppm) recorded
over the specified temperature range of –40°C to
+85°C.
Noise Performance (SNR)
The DAC1280 achieves excellent signal-to-noise ratio
(SNR) performance. The SNR figures were obtained
using the circuit of Figure 35. SNR is measured by
the ADS1282 over a bandwidth of 0 to 413Hz (with
1ms sampling). The ADC and DAC have
complementing gains for each measurement.
SNR is measured with a signal output of –0.5dBFS
and 31.25Hz, then taking the Fast Fourier
Transformation (FFT) of the ADC data, and
calculating the noise power over the specified
bandwidth. The dc, fundamental, and harmonic bins
are removed for the SNR calculations. Measured this
way, SNR is the combination of the individual noise
sources including ADC noise, DAC1280 noise,
voltage and current noise of the external op amp, and
thermal noise of the I/V resistors.
Copyright © 2010, Texas Instruments Incorporated
Product Folder Link(s): DAC1280
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