Datasheet

LTC2444/LTC2445/
LTC2448/LTC2449
12
2444589fc
For more information www.linear.com/LTC2444
The function of these bits is summarized in Table 1.
Table 1. LTC2444/LTC2445/LTC2448/LTC2449 Status Bits
INPUT RANGE
BIT 31
EOC
BIT 30
DMY
BIT 29
SIG
BIT 28
MSB
V
IN
≥ 0.5 • V
REF
0 0 1 1
0V ≤ V
IN
< 0.5 • V
REF
0 0 1 0
–0.5 • V
REF
≤ V
IN
< 0V 0 0 0 1
V
IN
< –0.5 • V
REF
0 0 0 0
Bits 28 to 5 are the 24-bit conversion result MSB first.
Bit 5 is the least significant bit (LSB).
Bits 4 to 0 are sub LSBs below the 24-bit level. Bits 4 to
0 may be included in averaging or discarded without loss
of resolution.
Data is shifted out of the SDO pin under control of the
serial clock (SCK), see Figure 3. Whenever CS is HIGH,
SDO remains high impedance and SCK is ignored.
In order to shift the conversion result out of the device,
CS must first be driven LOW. EOC is seen at the SDO pin
of the device once CS is pulled LOW. EOC changes real
time from HIGH to LOW at the completion of a conversion.
This signal may be used as an interrupt for an external
microcontroller. Bit 31 (EOC) can be captured on the first
rising edge of SCK. Bit 30 is shifted out of the device on
the first falling edge of SCK. The final data bit (Bit 0) is
shifted out on the falling edge of the 31st SCK and may
be latched on the rising edge of the 32nd SCK pulse. On
the falling edge of the 32nd SCK pulse, SDO goes HIGH
indicating the initiation of a new conversion cycle. This
bit serves as EOC (Bit 31) for the next conversion cycle.
Table 2 summarizes the output data format.
As long as the voltage on the IN
+
and IN
–
pins is main-
tained within the –0.3V to (V
CC
+ 0.3V) absolute maximum
operating range, a conversion result is generated for any
differential input voltage V
IN
from –FS = –0.5 • V
REF
to
+FS = 0.5 • V
REF
. For differential input voltages greater
than +FS, the conversion result is clamped to the value
corresponding to the +FS + 1LSB. For differential input
voltages below –FS, the conversion result is clamped to
the value corresponding to –FS – 1LSB.
SERIAL INTERFACE PINS
The LTC2444/LTC2445/LTC2448/LTC2449 transmit the
conversion results and receive the start of conversion
command through a synchronous 3- or 4-wire interface.
During the conversion and sleep states, this interface can
be used to assess the converter status and during the
data output state it is used to read the conversion result
and program the speed, resolution and input channel.
applicaTions inForMaTion
Table 2. LTC2444/LTC2445/LTC2448/LTC2449 Output Data Format
DIFFERENTIAL INPUT VOLTAGE
V
IN
*
BIT 31
EOC
BIT 30
DMY
BIT 29
SIG
BIT 28
MSB
BIT 27 BIT 26 BIT 25 … BIT 0
V
IN
* ≥ 0.5 • V
REF
** 0 0 1 1 0 0 0 … 0
0.5 • V
REF
** – 1LSB 0 0 1 0 1 1 1 … 1
0.25 • V
REF
** 0 0 1 0 1 0 0 … 0
0.25 • V
REF
** – 1LSB 0 0 1 0 0 1 1 … 1
0 0 0 1 0 0 0 0 … 0
–1LSB 0 0 0 1 1 1 1 … 1
–0.25 • V
REF
** 0 0 0 1 1 0 0 … 0
–0.25 • V
REF
** – 1LSB 0 0 0 1 0 1 1 … 1
–0.5 • V
REF
** 0 0 0 1 0 0 0 … 0
V
IN
* < –0.5 • V
REF
** 0 0 0 0 1 1 1 … 1
*The differential input voltage V
IN
= IN
+
– IN
–
. **The differential reference voltage V
REF
= REF
+
– REF
–
.