Datasheet

ADS7806
12
SBAS021B
www.ti.com
EXTERNAL DATA CLOCK
(After a Conversion)
After conversion ‘n’ is completed and the output registers
have been updated,
BUSY (pin 24) will go HIGH. With CS
LOW and R/C HIGH, valid data from conversion ‘n’ will be
output on SDATA (pin 19) synchronized to the external data
clock input on DATACLK (pin 18). The MSB will be valid on
the first falling edge and the second rising edge of the
external data clock. The LSB will be valid on the 12th falling
edge and 13th rising edge of the data clock. TAG (pin 20) will
input a bit of data for every external clock pulse. The first bit
input on TAG will be valid on SDATA on the 13th falling edge
and the 14th rising edge of DATACLK; the second input bit
will be valid on the 14th falling edge and the 15th rising edge,
etc. With a continuous data clock, TAG data will be output on
SDATA until the internal output registers are updated with
the results from the next conversion. Refer to Table V and
Figure 5.
EXTERNAL DATA CLOCK
(During a Conversion)
After conversion ‘n’ has been initiated, valid data from con-
version ‘n – 1’ can be read and will be valid up to 12µs after
the start of conversion ‘n’. Do not attempt to clock out data
from 12µs after the start of conversion ‘n’ until
BUSY (pin 24)
rises; this will result in data loss. NOTE: For the best possible
performance when using an external data clock, data should
not be clocked out during a conversion. The switching noise
of the asynchronous data clock can cause digital feedthrough
degrading the converter’s performance. Refer to Table VI
and Figure 6.
TAG FEATURE
TAG (pin 20) inputs serial data synchronized to the external
or internal data clock.
When using an external data clock, the serial bit stream input
on TAG will follow the LSB output on SDATA until the internal
output register is updated with new conversion results. See
Table VI and Figures 5 and 6.
The logic level input on TAG for the first rising edge of the
internal data clock will be valid on SDATA after all 12 bits of
valid data have been output.
INPUT RANGES
The ADS7806 offers three input ranges: standard ±10V, 0V-5V,
and a 0V-4V range for complete, single-supply systems. See
Figures 7a and 7b for the necessary circuit connections for
implementing each input range and optional offset and gain
adjust circuitry. Offset and full-scale error
(1)
specifications are
tested with the fixed resistors, see Figure 7b. Adjustments for
offset and gain are described in the Calibration section of this
data sheet.
The offset and gain are adjusted internally to allow external
trimming with a single supply. The external resistors compen-
sate for this adjustment and can be left out if the offset and
gain will be corrected in software (refer to the Calibration
section).
The input impedance, summarized in Table II, results from
the combination of the internal resistor network (see the front
page of this data sheet) and the external resistors used for
NOTE: (1) Full-scale error includes offset and gain errors measured at both
+FS and –FS.
FIGURE 6. Conversion and Read Timing with External Clock ( EXT/INT tied HIGH) Read During a Conversion.
EXTERNAL
DATACLK
CS
Bit 11 (MSB)
R/C
BUSY
DATA
TAG
Bit 0 (LSB) Tag 0 Tag 1
Tag 1 Tag 12 Tag 13 Tag 14Tag 0
t
20
t
21
t
1
t
11
t
3
t
17
t
18
t
19
t
22
t
20