DDC114 Datasheet, PDF (21/30 Pages) Burr-Brown (TI) – Quad Current Input 20-Bit ANALOG-TO-DIGITAL CONVERTER

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DATA FORMAT (FORMAT)
The serial output data is provided in an offset binary code
as shown in Table 9. The digital input pin FORMAT selects
how many bits are used in the output word. When
FORMAT is high (1), 20 bits are used. When FORMAT is
low (0), the lower 4 bits are truncated so that only 16 bits
are used. Note that the LSB size is 16 times bigger when
FORMAT = 0. An offset is included in the output to allow
slightly negative inputs, from board leakages for example,
from clipping the reading. This offset is approximately
0.4% of the positive full−scale.
Table 9. Ideal Output Code⁽¹⁾ vs Input Signal
INPUT
SIGNAL
IDEAL OUTPUT CODE
FORMAT = HIGH (1)
IDEAL OUTPUT CODE
FORMAT = LOW (0)
≥ 100% FS 1111 1111 1111 1111 1111 1111 1111 1111 1111
0.001531% FS 0000 0001 0000 0001 0000 0000 0001 0000 0001
0.001436% FS 0000 0001 0000 0000 1111 0000 0001 0000 0000
0.000191% FS 0000 0001 0000 0000 0010 0000 0001 0000 0000
0.000096% FS 0000 0001 0000 0000 0001 0000 0001 0000 0000
0% FS
0000 0001 0000 0000 0000 0000 0001 0000 0000
−0.3955% FS 0000 0000 0000 0000 0000 0000 0000 0000 0000
(1) _{Excludes the effects of noise, INL, offset, and gain errors.}
DDC114
SBAS255A − JUNE 2004 − REVISED NOVEMBER 2004
DATA RETRIEVAL
In both the continuous and non-continuous modes of
operation, the data from the last conversion is available for
retrieval on the falling edge of DVALID (see Figure 21 and
Table 10, on page 22). Data is shifted out of the falling
edge of the data clock, DCLK. Make sure not to retrieve
data around while CONV changes as this can introduce
noise. Stop activity on DCLK at least 10µs before or after
a CONV transition.
Setting the FORMAT pin = 0 (16-bit output word) will
reduce the time needed to retrieve data by 20% since there
are fewer bits to shift out. This can be useful in
multichannel systems requiring only 16 bits of resolution.
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