Datasheet
LTC2446/LTC2447
18
24467fa
Internal Serial Clock, Single Cycle Operation
This timing mode uses an internal serial clock to shift out
the conversion result and a CS signal to monitor and
control the state of the conversion cycle, see Figure 7.
In order to select the internal serial clock timing mode, the
EXT pin must be tied HIGH.
The serial data output pin (SDO) is Hi-Z as long as CS is
HIGH. At any time during the conversion cycle, CS may be
pulled LOW in order to monitor the state of the converter.
Once CS is pulled LOW, SCK goes LOW and EOC is output
to the SDO pin. EOC = 1 while a conversion is in progress
and EOC = 0 if the device is in the sleep state. Alternatively,
BUSY (Pin 2) may be used to monitor the status of the
conversion in progress. BUSY is HIGH during the conver-
Figure 7. Internal Serial Clock, Single Cycle Operation
sion and goes LOW at the conclusion. It remains LOW until
the result is read from the device.
When testing EOC, if the conversion is complete (EOC = 0),
the device will exit the sleep state and enter the data output
state if CS remains LOW. In order to prevent the device
from exiting the low power sleep state, CS must be pulled
HIGH before the first rising edge of SCK. In the internal
SCK timing mode, SCK goes HIGH and the device begins
outputting data at time t
EOCtest
after the falling edge of CS
(if EOC = 0) or t
EOCtest
after EOC goes LOW (if CS is LOW
during the falling edge of EOC). The value of t
EOCtest
is
500ns. If CS is pulled HIGH before time t
EOCtest
, the device
remains in the sleep state. The conversion result is held in
the internal static shift register.
APPLICATIO S I FOR ATIO
WUUU
MSB
BIT 28 BIT 27 BIT 26 BIT 25 BIT 24 BIT 23 BIT 22 BIT 21 BIT 20 BIT 19 BIT 0
LSB
Hi-Z
244676 F07
SIG
BIT 29
“0”
BIT 30
EOC
Hi-Z
CS
SCK
SDI
SDO
BUSY
BIT 31
1 0 EN SGL GLBL A1 A0 OSR3 OSR2 OSR1 OSR0 TWOXODD
1234567891011121314 32
CONVERSION
SLEEP DATA OUTPUT CONVERSION
TEST EOC TEST EOC
DON'T CARE DON'T CARE
<t
EOC(TEST)
V
CC
F
O
REF67
+
REF67
–
CH0
CH1
CH2
CH7
COM
REFG
+
REFG
–
REF01
+
REF01
–
SCK
SDI
SDO
CS
GND
28
29
30
11
10
35
24
23
8
9
12
22
7
38
37
1,4,5,6,31,32,33
36
34
USER SELECTABLE
REFERENCES
0.1V TO V
CC
ANALOG
INPUTS
.
.
.
.
.
.
2
= EXTERNAL OSCILLATOR
= INTERNAL OSCILLATOR
1µF
4.5V TO 5.5V
LTC2446
4-WIRE
SPI INTERFACE
BUSY