Datasheet

LTC2487
16
2487fd
INPUT DATA FORMAT
The serial input word to the LTC2487 is 16 bits long and
is written into the device input register in two 8-bit words.
The fi rst word (SGL, ODD, A2, A1, A0) is used to select
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.
After power-up, the device initiates an internal reset cycle
which sets the input channel to CH0-CH1 (IN
+
= CH0, IN
–
=
CH1), the frequency rejection to simultaneous 50Hz/60Hz,
and 1x output rate (auto-calibration enabled), and gain = 1.
The fi rst conversion automatically begins at power-up using
this default confi guration. Once the conversion is complete,
up to two words may be written into the device.
The fi rst three bits of the fi rst 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.
If the fi rst three bits are 000 or 100, the following data is ig-
nored (don’t care) and the previously selected input channel
and confi guration remain 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).
Figure 3a. Timing Diagram for Reading from the LTC2487
APPLICATIONS INFORMATION
Figure 3b. Timing Diagram for Writing to the LTC2487
DATA INPUT
ACK BY
LTC2487
ACK BY
LTC2487
ACK BY
LTC2487
(OPTIONAL 2ND BYTE)
START BY
MASTER
SGL ODD
W
0
1
SCL
SDA
EN A2 A1 A0
7…892
123456789
1
7-BIT ADDRESS
2487 F03b
IM FAEN2 FB SPD GS2 GS1 GS0
SLEEP
19
234 56 78
SLEEP DATA OUTPUT
ACK BY
LTC2487
ACK BY
MASTER
ALWAYS LOW
START BY
MASTER
NAK BY
MASTER
LSBR MSBSIG
D23
7 … …89
1 2 9
1 2 3 4 5 6 7 8 9
1
7-BIT
ADDRESS
2487 F03a
SCL
SDA
Table 3. Channel Selection
MUX ADDRESS CHANNEL SELECTION
SGL
ODD/
SIGN A2 A1 A0 0 1 2 3 COM
*00000IN
+
IN
–
00001 IN
+
IN
–
01000IN
–
IN
+
01001 IN
–
IN
+
10000IN
+
IN
–
10001 IN
+
IN
–
11000 IN
+
IN
–
11001 IN
+
IN
–
*Default at power up