−2

−1

0

1

2

−2

0

2

4

6

8

10

12

14

16

18

SYNC pin transition

Time (µs)

VOUTP, VOUTN

Pulse mode

Full Scale Step

G000

−0.5

−0.4

−0.3

−0.2

−0.1

0

0.1

0.2

0.3

0.4

0.5

−50

0

50

100

150

200

250

300

350

400

450

SYNC pin transition

Time (µs)

(VOUTP − VOUTN)

Pulse Mode

Full scale step

G000

DAC1282

www.ti.com

SBAS490

– DECEMBER 2011

DC Noise

DC noise data are obtained using the DAC circuit of Figure 50 with data captured by the ADS1282. The noise is

measured in dc mode with the output voltage set to 0 V differential. The ADC gain is set to the complement of

the DAC gain for each output range. The noise is the standard deviation of 4096-point ADC acquisition record

(RMS noise, referred-to-output).

Total Harmonic Distortion (THD)

The DAC1282 achieves excellent THD performance. The THD data are obtained using the DAC circuit of

Figure 50 and captured by the ADS1282. The ADC gain is set to the complement of the DAC gain for each

output range.

THD is measured with a

–0.5-dBFS output signal level and a 31.25-Hz test frequency, then taking the FFT of the

4096-point ADC acquisition record. The ADC data points are increased to 16,384 for gains of 1/16, 1/32, and

1/64 for improved rendition of harmonics as a result of the higher noise floor. The THD measurement represents

the combination of the ADS1282 THD and the DAC1282 THD.

STEP RESPONSE

The step response of the DAC depends on the mode. In pulse mode, the DAC disables the external analog filter

formed by capacitors CAPP, CAPN. Disabling the analog filter in conjunction with the fast response pulse DAC

results in noticeably faster rise time and shorter settling time. Note that additional filter components in the signal

path may also affect the response time.

Figure 44 shows the pulse mode step response after the SYNC pin transition. Figure 45 shows the pulse mode

detail settling to 0.1% of final value after the SYNC pin transition.

Figure 44. Pulse Mode Step Response

Figure 45. Pulse Mode Step Response Detail

Copyright

© 2011, Texas Instruments Incorporated

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