LTC2446 LINER [Linear Technology], LTC2446 Datasheet - Page 17

• 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
External Serial Clock, 3-Wire I/O
This timing mode utilizes a 3-wire serial I/O interface. The
conversion result is shifted out of the device by an exter-
nally generated serial clock (SCK) signal, see Figure 6. CS
may be permanently tied to ground, simplifying the user
interface or isolation barrier. The external serial clock
mode is selected by tying EXT LOW.
Since CS is tied LOW, the end-of-conversion (EOC) can be
continuously monitored at the SDO pin during the convert
and sleep states. Conversely, BUSY (Pin 2) may be used
to monitor the status of the conversion cycle. EOC or BUSY
may be used as an interrupt to an external controller
(EXTERNAL)
BUSY
SDO
SCK
SDI
CS
CONVERSION
DON'T CARE
U
SLEEP
U
1
BIT 31
EOC
1
USER SELECTABLE
2
BIT 30
Figure 6. External Serial Clock, CS = 0 Operation (3-Wire)
“0”
REFERENCES
0
0.1V TO V
W
ANALOG
INPUTS
3
BIT 29
SIG
EN
1µF
4.5V TO 5.5V
CC
4
BIT 28 BIT 27 BIT 26 BIT 25 BIT 24 BIT 23 BIT 22 BIT 21
MSB
SGL
28
29
30
11
10
24
23
12
22
8
9
7
U
5
V
REFG
REFG
REF01
REF01
REF67
REF67
CH0
CH1
CH2
CH7
COM
ODD
CC
. .
.
. . .
LTC2446
+
–
+
–
+
–
6
GLBL
BUSY
SDO
GND
SCK
SDI
CS
F
O
7
37
2
1,4,5,6,31,32,33
34
38
35
36
A1
DATA OUTPUT
indicating the conversion result is ready. EOC = 1
(BUSY = 1) while the conversion is in progress and
EOC = 0 (BUSY = 0) once the conversion enters the low
power sleep state. On the falling edge of EOC/BUSY, the
conversion result is loaded into an internal static shift
register. The device remains in the sleep state until the
first rising edge of SCK. Data is shifted out the SDO pin
on each falling edge of SCK enabling external circuitry to
latch data on the rising edge of SCK. EOC can be latched
on the first rising edge of SCK. On the 32nd falling edge
of SCK, SDO and BUSY go HIGH (EOC = 1) indicating a
new conversion has begun.
8
A0
3-WIRE
SPI INTERFACE
9
= EXTERNAL OSCILLATOR
= INTERNAL OSCILLATOR
OSR3
10
OSR2
11
OSR1
LTC2446/LTC2447
12
BIT 20 BIT 19
OSR0 TWOX
13
14
DON'T CARE
BIT 0
32
LSB
24467 F06
CONVERSION
17
24467fa