LTC2492 Linear Technology, LTC2492 Datasheet - Page 18

• Manufacturer Part Number: LTC2492
• Description: 24-Bit 2-/4-Channel ADC
• Manufacturer: Linear Technology

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APPLICATIONS INFORMATION
LTC2492
Table 2. Output Data Format
Differential Input Voltage
V
V
0.5 • V
0.25 • V
0.25 • V
0
–1LSB
–0.25 • V
–0.25 • V
–0.5 • V
V
*The differential input voltage V
** Sub LSBs are below the 24-bit level. They may be included in averaging, or discarded without loss of resolution.
conversion automatically begins at power up using this
default confi guration. Once the conversion is complete,
a new word may be written into the device.
The fi rst three bits shifted into the device consist of two
preamble bits and an enable bit. These bits are used to
enable the device confi guration and input channel selection.
Valid settings for these three bits are 000, 100 and 101.
Other combinations should be avoided. If the fi rst three bits
are 000 or 100, the following data is ignored (don’t care)
and the previously selected input channel and confi guration
remain valid for the next conversion.
If the fi rst three bits shifted into the device are 101, then
the next fi ve bits select the input channel for the next
conversion cycle (see Table 3).
Table 3 Channel Selection
*Default at power up
18
IN
IN
IN
SGL
*0
0
0
0
1
1
1
1
*
* ≥ 0.5 • V
* < –0.5 • V
REF
REF
REF
REF
ODD/
SIGN
REF
REF
** – 1LSB
0
0
1
1
0
0
1
1
MUX ADDRESS
**
** – 1LSB
**
**
** – 1LSB
REF
REF
**
A2
**
0
0
0
0
0
0
0
0
IN
A1
0
0
0
0
0
0
0
0
= IN
+
– IN
A0
0
1
0
1
0
1
0
1
–
. **The differential reference voltage V
IN
IN
IN
0
+
+
–
`E`O`C
Bit 31
CHANNEL SELECTION
0
0
0
0
0
0
0
0
0
0
IN
IN
IN
1
+
+
–
IN
IN
IN
Bit 30
DMY
2
+
–
+
0
0
0
0
0
0
0
0
0
0
IN
IN
IN
3
+
+
–
REF
Bit 29
SIG
= REF
1
1
1
1
1
0
0
0
0
0
COM
IN
IN
IN
IN
–
–
–
–
+
– REF
Bit 28
MSB
–
.
1
0
0
0
0
1
1
1
1
0
The fi rst input bit (SGL) following the 101 sequence
determines if the input selection is differential (SGL =
0) or single-ended (SGL = 1). For SGL = 0, two adjacent
channels can be selected to form a differential input. For
SGL = 1, one of four channels is selected as the positive
input. The negative input is COM for all single-ended
operations. The remaining four bits (ODD, A2, A1, A0)
determine which channel(s) is/are selected and the polarity
(for a differential input).
The next serial input bit immediately following the input
channel selection is the enable bit for the conversion
confi guration (EN2). If this bit is set to 0, then the next
conversion is performed using the previously selected
converter confi guration.
A new confi guration can be loaded into the device by
setting EN2 = 1 (see Table 4). The fi rst bit (IM) is used
to select the internal temperature sensor. If IM = 1, the
following conversion will be performed on the internal
temperature sensor rather than the selected input channel.
The next two bits (FA and FB) are used to set the rejection
frequency. The fi nal bit (SPD) is used to select either the
1x output rate if SPD = 0 (auto-calibration is enabled and
the offset is continuously calibrated and removed from
the fi nal conversion result) or the 2x output rate if SPD
= 1 (offset calibration disabled, multiplexing output rates
up to 15Hz with no latency). When IM = 1 (temperature
measurement) SPD will be ignored and the device will
operate in 1× mode. The confi guration remains valid until
Bit 27
0
1
1
0
0
1
1
0
0
1
Bit 26
0
1
0
1
0
1
0
1
0
1
Bit 25
0
1
0
1
0
1
0
1
0
1
…
…
…
…
…
…
…
…
…
…
…
Bit 5
LSB
0
1
0
1
0
1
0
1
0
1
Bits 4 to 0
SUB LSBs
XXXXX
XXXXX
XXXXX
XXXXX
XXXXX
XXXXX
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00000
11111
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