LTC1856 Linear Technology, LTC1856 Datasheet - Page 18

• Manufacturer Part Number: LTC1856
• Description: 100ksps ADC Converters
• Manufacturer: Linear Technology

www.DataSheet4U.com
APPLICATIO S I FOR ATIO
LTC1854/LTC1855/LTC1856
SERIAL DATA INPUT (SDI) INTERFACE
The LTC1854/LTC1855/LTC1856 communicate with mi-
croprocessors and other external circuitry via a synchro-
nous, full duplex, 3-wire serial interface (see Figure 7).
The shift clock (SCK) synchronizes the data transfer with
each bit being transmitted on the falling SCK edge and
captured on the rising SCK edge in both transmitting and
receiving systems. The data is transmitted and received
simultaneously (full duplex).
An 8-bit input word is shifted into the SDI input which
configures the LTC1854/LTC1855/LTC1856 for the next
conversion. Simultaneously, the result of the previous
conversion is output on the SDO line. At the end of the data
exchange the requested conversion begins by applying a
rising edge on CONVST. After t
complete and the results will be available on the next data
transfer cycle. As shown below, the result of a conversion
SGL/
18
Table 1. Multiplexer Channel Selection
DIFF
CHANNEL
0
0
0
0
0
0
0
0
0,1
2,3
4,5
6,7
MUX ADDRESS
{
{
{
{
SIGN
ODD
0
0
0
0
1
1
1
1
4 Differential
+
–
+
–
+
–
+
–
SELECT
1 0
0
0
1
1
0
0
1
1
(
(
(
(
(
(
(
(
–
+
–
+
–
+
–
+
)
)
)
)
)
)
)
)
0
1
0
1
0
1
0
1
U
0
+
–
DIFFERENTIAL CHANNEL SELECTION
1
–
+
Figure 8. Examples of Multiplexer Options on the LTC1854/LTC1855/LTC1856
U
CHANNEL
0
1
2
3
4
5
6
7
2
+
–
CONV
8 Single-Ended
+
+
+
+
+
+
+
+
COM (
W
3
–
+
, the conversion is
–
)
4
+
–
5
–
+
U
+
–
6
CHANNEL
0,1
2,3
Differential and Single-Ended
4
5
6
7
{
{
–
+
7
Combinations of
SGL/
DIFF
+
–
–
+
+
+
+
+
COM (
is delayed by one conversion from the input word re-
questing it.
INPUT DATA WORD
The LTC1854/LTC1855/LTC1856 8-bit data word is clocked
into the SDI input on the first eight rising SCK edges.
Further inputs on the SDI pin are then ignored until the next
conversion. The eight bits of the input word are defined as
follows:
SDI
SDO
1
1
1
1
1
1
1
1
MUX ADDRESS
SGL/
DIFF
–
SIGN
ODD
)
SDO WORD 0
SDI WORD 1
0
0
0
0
1
1
1
1
TRANSFER
DATA
SIGN
MUX ADDRESS
ODD
SELECT
1 0
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
CONVERSION
SELECT
4,5
6,7
1
t
{
{
CONV
A/D
0
+
SINGLE-ENDED CHANNEL SELECTION
SELECT
1ST CONVERSION
+
1
+
–
+
–
COM (UNUSED)
0
SDI WORD 2
SDO WORD 1
TRANSFER
MUX Assignment “On the Fly”
2
+
DATA
DON'T
CARE
3
+
Changing the
CONVERSION
4
+
4,5
DON'T
CARE
t
CONV
A/D
6
7
{
+
5
2ND CONVERSION
COM (
+
–
+
+
+
6
SDI WORD 3
SDO WORD 2
NAP
POWER DOWN
SELECTION
–
+
7
)
18545 AI02
18545 F08
185456fa
SLEEP
COM
18545 AI03
–
–
–
–
–
–
–
–