Datasheet

LTC2446/LTC2447
10
24467fa
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
24467 F03
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
+FS, the conversion result is clamped to the value corre-
sponding 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 LTC2446/LTC2447 transmit the conversion results
and receive the start of conversion command through a
synchronous 3- or 4-wire interface. During the conver-
sion 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.
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 maintained
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
Table 2. LTC2446/LTC2447 Output Data Format
Differential Input Voltage Bit 31 Bit 30 Bit 29 Bit 28 Bit 27 Bit 26 Bit 25 … Bit 0
V
IN
* EOC DMY SIG MSB
V
IN
* ≥ 0.5 • V
REF
** 00110 0 0…0
0.5 • V
REF
** – 1LSB 0 0101 1 1…1
0.25 • V
REF
** 0 0101 0 0…0
0.25 • V
REF
** – 1LSB 0 0100 1 1…1
0 0 0100 0 0…0
–1LSB 0 0011 1 1…1
–0.25 • V
REF
** 0 0011 0 0…0
–0.25 • V
REF
** – 1LSB 00010 1 1…1
–0.5 • V
REF
** 0 0010 0 0…0
V
IN
* < –0.5 • V
REF
** 00001 1 1…1
*The differential input voltage V
IN
= IN
+
– IN
–
. **The differential reference voltage V
REF
= REF
+
– REF
–
.
APPLICATIO S I FOR ATIO
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Figure 3. SDI Speed/Resolution, Channel Selection, and Data Output Timing