ADS5281IPFPR datasheet(20/44 Pages) TI

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LOW-FREQUENCY NOISE SUPPRESSION MODE

ANALOG INPUT INVERT

LVDS TEST PATTERNS

ADS5281

ADS5282

SBAS397H – DECEMBER 2006 – REVISED MARCH 2008

ADDRESS

IN HEX

D15

D14

D13

D12

D11

D10

NAME

LFNS_CH<8:1>

The low-frequency noise suppression mode is specifically useful in applications where good noise performance is

desired in the frequency band of 0MHz to 1MHz (around dc). Setting this mode shifts the low-frequency noise of

the ADS528x to approximately fS/2, thereby moving the noise floor around dc to a much lower value.

LFNS_CH<8:1> enables this mode individually for each channel.

ADDRESS

IN HEX

D15

D14

D13

D12

D11

D10

NAME

INVERT_CH<8:1>

Normally, the INP pin represents the positive analog input pin, and INN represents the complementary negative

input. Setting the bits marked INVERT_CH<8:1> (individual control for each channel) causes the inputs to be

swapped. INN now represents the positive input, and INP the negative input.

ADDRESS

IN HEX

D15

D14

D13

D12

D11

D10

NAME

EN_RAMP

DUALCUSTOM_PAT

SINGLE_CUSTOM_PAT

BITS_CUSTOM1<11:10>

BITS_CUSTOM2<11:10>

BITS_CUSTOM1<9:0>

BITS_CUSTOM2<9:0>

PAT_DESKEW

PAT_SYNC

The ADS528x can output a variety of test patterns on the LVDS outputs. These test patterns replace the normal

ADC data output. Setting EN_RAMP to '1' causes all the channels to output a repeating full-scale ramp pattern.

The ramp increments from zero code to full-scale code in steps of 1LSB every clock cycle. After hitting the

full-scale code, it returns back to zero code and ramps again.

The device can also be programmed to output a constant code by setting SINGLE_CUSTOM_PAT to '1', and

programming the desired code in BITS_CUSTOM1<11:0>. In this mode, BITS_CUSTOM1<11:0> take the place

of the 12-bit ADC data at the output, and are controlled by LSB-first and MSB-first modes in the same way as

normal ADC data are.

The device may also be made to toggle between two consecutive codes by programming DUAL_CUSTOM_PAT

to '1'. The two codes are represented by the contents of BITS_CUSTOM1<11:0> and BITS_CUSTOM2<11:0>.

In addition to custom patterns, the device may also be made to output two preset patterns:

1. Deskew patten: Set using PAT_DESKEW, this mode replaces the 12-bit ADC output D<11:0> with the

010101010101 word.

2. Sync pattern: Set using PAT_SYNC, the normal ADC word is replaced by a fixed 111111000000 word.

Note that only one of the above patterns should be active at any given instant.

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