LTC2487
applicaTions inForMaTion
the input channel. The second word of data (IM, FA, FB,
SPD, GS2, GS1, GS0) is used to select the frequency
rejection, speed mode (1x, 2x), temperature measure-
ment, and gain.
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).
Table 3 Channel Selection
MUX ADDRESS
ODD/
SGL SIGN A2
CHANNEL SELECTION
After power-up, the device initiates an internal reset cycle
+
–
whichsetstheinputchanneltoCH0-CH1(IN =CH0, IN =
CH1),thefrequencyrejectiontosimultaneous50Hz/60Hz,
and1xoutputrate(auto-calibrationenabled),andgain=1.
Thefirstconversionautomaticallybeginsatpower-upusing
thisdefaultconfiguration.Oncetheconversioniscomplete,
up to two words may be written into the device.
A1
0
A0
0
0
1
2
IN
IN
IN
3
IN
IN
COM
+
–
+
–
*0
0
0
0
1
1
0
0
1
1
0
0
0
0
0
0
0
0
IN
IN
+
–
+
–
+
0
1
+
0
0
0
IN
IN
IN
IN
0
0
1
–
1
0
0
IN
–
The first three bits of the first input word consist of two
preamble bits and one enable bit. Valid settings for these
three bits are 000, 100, and 101. Other combinations
should be avoided.
1
0
1
IN
+
–
1
0
0
IN
+
–
1
0
1
IN
IN
*Default at power up
If the first three bits are 000 or 100, the following data is ig-
nored(don’tcare)andthepreviouslyselectedinputchannel
and configuration remain valid for the next conversion.
The first input bit (SGL) following the 101 sequence de-
termines if the input selection is differential (SGL = 0) or
single-ended(SGL=1).ForSGL=0,twoadjacentchannels
1
…
7
8
9
1
2
…
9
1
2
3
4
5
6
7
8
9
SCL
SDA
7-BIT
ADDRESS
R
SIG
MSB
D23
LSB
ACK BY
LTC2487
ACK BY
MASTER
NAK BY
MASTER
START BY
MASTER
ALWAYS LOW
2487 F03a
SLEEP
DATA OUTPUT
Figure 3a. Timing Diagram for Reading from the LTC2487
1
2
…
7
8
9
1
9
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
9
SCL
SDA
1
0
EN
SGL ODD
A2
A1 A0
EN2 IM
FA FB SPD GS2 GS1 GS0
W
7-BIT ADDRESS
ACK BY
LTC2487
ACK BY
LTC2487
(OPTIONAL 2ND BYTE)
ACK BY
LTC2487
START BY
MASTER
2487 F03b
SLEEP
DATA INPUT
Figure 3b. Timing Diagram for Writing to the LTC2487
2487fa
ꢀꢅ
Linear [ Linear ]
