LTC2497 Datasheet, PDF (15/28 Pages) Linear Technology – 16-Bit 8-/16-Channel ΔΣ ADC with Easy Drive Input Current Cancellation and I2C Interface

LTC2497
APPLICATIONS INFORMATION
INPUT DATA FORMAT
The LTC2497 serial input is 8 bits long and is written into
the device in one 8-bit word. SGL, ODD, A2, A1, A0 are
used to select the input channel.
After power-up, the device initiates an internal reset cycle
which sets the input channel to CH0-CH1 (IN⁺ = CH0,
IN^– = CH1). The first conversion automatically begins
at power-up using this default input channel. Once the
conversion is complete, a new channel may be written
into the device.
The first three bits of the input word consist of two pre-
amble bits and one enable bit. These three bits are used
to enable the input channel selection. Valid settings for
these three bits are 000, 100, and 101. Other combinations
should be avoided.
If the first three bits are 000 or 100, the following data
is ignored (don’t care) and the previously selected input
channel remains valid for the next conversion.
If the first three bits shifted into the device are 101, then
the next five bits select the input channel for the next
conversion cycle (see Table 3).
The first input bit (SGL) following the 101 sequence de-
termines if the input selection is differential (SGL = 0) or
single-ended (SGL = 1). For SGL = 0, two adjacent chan-
nels can be selected to form a differential input. For SGL
= 1, one of 16 channels is selected as the positive input.
The negative input is COM for all single-ended operations.
The remaining four bits (ODD, A2, A1, A0) determine
which channel(s) is/are selected and the polarity (for a
differential input).
SCL
1… 7
8
9
1
2…
9
1
2
3
4
5
6
7
89
SDA
START BY
MASTER
7-BIT
ADDRESS
R
SGN
ACK BY
LTC2497
MSB D15
ACK BY
MASTER
SLEEP
LSB
DATA OUTPUT
ALWAYS LOW
Figure 3a. Timing Diagram for Reading from the LTC2497
NAK BY
MASTER
2497 F03a
SCL
1 2… 7 8 9
1 2 3 4 5 6 7 89
1 2 3 4 5 6 7 89
SDA
START BY
MASTER
7-BIT ADDRESS W
1 0 EN SGL ODD A2 A1 A0
XXXXXXXX
SLEEP
ACK BY
LTC2497
ACK BY
LTC2497
DATA INPUT
Figure 3b. Timing Diagram for Writing to the LTC2497
NAK BY
LTC2497
2497 F03b
2497f
15