Datasheet

10
LTC1090
1090fc
Data transfer is initiated by a falling chip select (CS) signal.
After the falling CS is recognized, an 8-bit input word
is shifted into the D
IN
input which configures the LTC1090
for the next conversion. Simultaneously, the result of the
previous conversion is output on the D
OUT
line. At the end
of the data exchange the requested conversion begins and
CS should be brought high. After t
CONV
, the conversion is
complete and the results will be available on the next data
transfer cycle. As shown below, the result of a conversion
is delayed by one CS cycle from the input word requesting
it.
2. Input Data Word
The LTC1090 8-bit input data word is clocked into the D
IN
input on the first eight rising SCLK edges after chip select
is recognized. Further inputs on the D
IN
pin are then
ignored until the next CS cycle. The eight bits of the input
word are defined as follows:
Multiplexer (MLIX) Address
The first four bits of the input word assign the MUX
configuration for the requested conversion. For a given
channel selection, the converter will measure the voltage
between the two channels indicated by the + and – signs
in the selected row of Table 1. Note that in differential
mode (SGL/DIFF = O) measurements are limited to four
adjacent input pairs with either polarity. In single ended
mode, all input channels are measured with respect to
COM. Figure 1 shows some examples of multiplexer
assignments.
Table 1. Multiplexer Channel Selection
MUX ADDRESS DIFFERENTIAL CHANNEL SELECTION
SGL/ ODD SELECT
DIFF SIGN 1 0 0 1 234567
0000+–
0001 +–
0010 +–
0011 +–
0100–+
0101 –+
0110 –+
0111 –+
MUX ADDRESS SINGLE ENDED CHANNEL SELECTION
SGL/ ODD/ SELECT
DIFF SIGN 1 0 0 1 2 3 4 5 6 7 COM
1000+ –
1001 + –
1010 + –
1011 + –
1100 + –
1101 + –
1110 + –
1111 +–
APPLICATIO S I FOR ATIO
WUUU
LTC1090 • AI02
Data
Transfer
t
CONV
A/D
Conversion
D
OUT
D
IN
D
IN
Word 1
D
OUT
Word 0
t
CONV
A/D
Conversion
Data
Transfer
D
IN
Word 2
D
OUT
Word 1
D
IN
Word 3
D
OUT
Word 2
LTC1090• AI03
Data Input (D
IN
) Word:
ODD/
SIGN
SELECT
1
SELECT
0
UNI MSBF WL1
Word Length
MUX Address
Unipolar/
Bipolar
MSB First/
LSB First
WL0
SGL/
DIFF