LTC2446 LINER [Linear Technology], LTC2446 Datasheet - Page 20

• Manufacturer Part Number: LTC2446
• Description: 24-Bit High Speed 8-Channel ?? ADCs with Selectable Multiple Reference Inputs
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
LTC2446/LTC2447
Internal Serial Clock, 3-Wire I/O,
Continuous Conversion
This timing mode uses a 3-wire, all output (SCK and SDO)
interface. The conversion result is shifted out of the device
by an internally generated serial clock (SCK) signal, see
Figure 9. CS may be permanently tied to ground, simplify-
ing the user interface or isolation barrier. The internal
serial clock mode is selected by tying EXT HIGH.
During the conversion, the SCK and the serial data output
pin (SDO) are HIGH (EOC = 1) and BUSY = 1. Once the
conversion is complete, SCK, BUSY and SDO go LOW
(EOC = 0) indicating the conversion has finished and the
BUSY
20
SDO
SCK
SDI
CS
DON'T CARE
CONVERSION
U
BIT 31
EOC
U
1
1
SLEEP
BIT 30
“0”
0
2
BIT 29
W
USER SELECTABLE
Figure 9. Internal Serial Clock, Continuous Operation
SIG
EN
3
REFERENCES
0.1V TO V
BIT 28 BIT 27 BIT 26 BIT 25 BIT 24 BIT 23 BIT 22 BIT 21
MSB
SGL
ANALOG
4
INPUTS
1µF
4.5V TO 5.5V
CC
ODD
U
5
28
29
30
11
10
24
23
12
22
GLBL
8
9
7
6
V
REFG
REFG
REF01
REF01
REF67
REF67
CH0
CH1
CH2
CH7
COM
CC
. . .
. . .
LTC2446
+
–
A1
+
–
+
–
7
DATA OUTPUT
BUSY
GND
SDO
SCK
SDI
CS
device has entered the low power sleep state. The part
remains in the sleep state a minimum amount of time
(≈500ns) then immediately begins outputting data. The
data output cycle begins on the first rising edge of SCK and
ends after the 32nd rising edge. Data is shifted out the SDO
pin on each falling edge of SCK. The internally generated
serial clock is output to the SCK pin. This signal may be
used to shift the conversion result into external circuitry.
EOC can be latched on the first rising edge of SCK and the
last bit of the conversion result can be latched on the 32nd
rising edge of SCK. After the 32nd rising edge, SDO goes
HIGH (EOC = 1) indicating a new conversion is in progress.
SCK remains HIGH during the conversion.
F
O
A0
8
37
2
1,4,5,6,31,32,33
34
38
35
36
OSR3
9
3-WIRE
SPI INTERFACE
OSR2
10
= EXTERNAL OSCILLATOR
= INTERNAL OSCILLATOR
OSR1
11
BIT 20 BIT 19
OSR0 TWOX
12
13
14
DON'T CARE
BIT 0
LSB
32
24467 F09
CONVERSION
24467fa