ADS5281IPFPR datasheet(24/44 Pages) TI

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EN_SDR= '1',FALL_SDR='0'

EN_SDR= '1',FALL_SDR='1'

ADCLK

LCLK

OUT

ADCLK

LCLK

OUT

DATA OUTPUT FORMAT MODES

ADS5281

ADS5282

SBAS397H – DECEMBER 2006 – REVISED MARCH 2008

In addition to programming the phase of LCLK in the DDR mode, the device can also be made to operate in SDR

mode by setting the EN_SDR bit to '1'. In this mode, the bit clock (LCLK) is output at 12x times the input clock, or

twice the rate as in DDR mode. Depending on the state of FALL_SDR, LCLK may be output in either of the two

manners shown in Figure 3. As can be seen in Figure 3, only the LCLK rising (or falling) edge is used to capture

the output data in SDR mode.

Figure 3. SDR Interface Modes

The SDR mode does not work well beyond 40MSPS because the LCLK frequency becomes very high.

The ADC output, by default, is in straight offset binary mode. Programming the BTC_MODE bit to '1' inverts the

MSB, and the output becomes binary two's complement mode.

Also by default, the first bit of the frame (following the rising edge of ADCLKP) is the LSB of the ADC output.

Programming the MSB_FIRST mode inverts the bit order in the word, and the MSB is output as the first bit

following the ADCLKP rising edge.

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