Datasheet

LTC2493
16
2493fd
DATA OUTPUT FORMAT
The output register contains the last conversion result.
After each conversion is completed, the device automati-
cally enters the sleep state where the supply current is
reduced to 1µA. When the LTC2493 is addressed for a read
operation, it acknowledges (by pulling SDA low) and acts
as a transmitter. The master/receiver can read up to four
bytes from the LTC2493. After a complete read operation
(4 bytes), a new conversion is initiated. The device will
NACK subsequent read operations while a conversion is
being performed.
The data output stream is 32 bits long and is shifted out
on the falling edges of SCL (see Figure 3a). The first bit
is the conversion result sign bit (SIG) (see Tables 1 and
2). This bit is high if V
IN
≥ 0 and low if V
IN
< 0 (where V
IN
corresponds to the selected input signal IN
+
– IN
–
). The
second bit is the most significant bit (MSB) of the result.
The first two bits (SIG and MSB) can be used to indicate
over and under range conditions (see Table 2). If both bits
are high, the differential input voltage is equal to or above
+FS. If both bits are set low, the input voltage is below –FS.
Table 1. Output Data Format
DIFFERENTIAL INPUT VOLTAGE
V
IN
*
BIT 31
SIG
BIT 30
MSB
BIT 29 BIT 28 BIT 27 … BIT 6
LSB
BITS 5-0
Sub LSBs
V
IN
* ≥ FS** 1 1 0 0 0 … 0 00000
FS** – 1 LSB 1 0 1 1 1 … 1 XXXXX
0.5 • FS** 1 0 1 0 0 … 0 XXXXX
0.5 • FS** – 1 LSB 1 0 0 1 1 … 1 XXXXX
0 1/0
†
0 0 0 0 … 0 XXXXX
–1 LSB 0 1 1 1 1 … 1 XXXXX
–0.5 • FS** 0 1 1 0 0 … 0 XXXXX
–0.5 • FS** – 1 LSB 0 1 0 1 1 … 1 XXXXX
–FS** 0 1 0 0 0 … 0 XXXXX
V
IN
* < –FS** 0 0 1 1 1 … 1 11111
*The differential input voltage V
IN
= IN
+
– IN
–
.
**The full-scale voltage FS = 0.5 • V
REF
. Sub LSBs are below the 24-bit level. They may be included in averaging, or discarded without loss of resolution.
†
The sign bit changes state during the 0 output code when the device is operating in the 2x speed mode.
The function of these bits is summarized in Table 2. The
24 bits following the MSB bit are the conversion result in
binary two’s, complement format. The remaining six bits
are sub LSBs below the 24-bit level.
As long as the voltage on the selected input channels (IN
+
and IN
–
) remains between –0.3V and V
CC
+ 0.3V (absolute
maximum operating range) a conversion result is gener-
ated 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 +FS. For differential input volt-
ages below –FS, the conversion result is clamped to the
value –FS – 1 LSB.
Table 2. LTC2493 Status Bits
INPUT RANGE
BIT 31
SIG
BIT 30
MSB
V
IN
≥ FS 1 1
0V ≤ V
IN
< FS 1/ 0 0
–FS ≤ V
IN
< 0V 0 1
V
IN
< –FS 0 0
applicaTions inForMaTion