LTC2497 Linear Technology, LTC2497 Datasheet - Page 15

• Manufacturer Part Number: LTC2497
• Description: 16-Bit 8-/16-Channel ADC
• Manufacturer: Linear Technology

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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
IN
at power-up using this default input channel. Once the
conversion is complete, a new channel may be written
into the device.
The fi rst 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.
SCL
SDA
–
SCL
SDA
START BY
MASTER
= CH1). The fi rst conversion automatically begins
START BY
MASTER
ADDRESS
1
1
7-BIT
7-BIT ADDRESS
…
2
7
SLEEP
…
SLEEP
8
7
R
W
LTC2497
ACK BY
8
LTC2497
ACK BY
Figure 3a. Timing Diagram for Reading from the LTC2497
9
Figure 3b. Timing Diagram for Writing to the LTC2497
9
SGN
1
1
1
MSB
0
+
2
2
= CH0,
EN
…
D15
3
SGL ODD
MASTER
ACK BY
4
9
5
If the fi rst 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 fi rst three bits shifted into the device are 101, then
the next fi ve bits select the input channel for the next
conversion cycle (see Table 3).
The fi rst 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).
A2
1
6
A1
7
LSB
DATA INPUT
DATA OUTPUT
2
A0
8
LTC2497
ACK BY
9
3
X
1
4
X
2
ALWAYS LOW
5
X
3
X
4
6
5
X
LTC2497
7
6
X
7
X
8
MASTER
NAK BY
8
X
LTC2497
15
NAK BY
9
2497 F03a
2497 F03b
9
2497f