LTC2488 LINER [Linear Technology], LTC2488 Datasheet - Page 14

• Manufacturer Part Number: LTC2488
• Description: 16-Bit 2-/4-Channel ?? ADC with Easy Drive Input Current Cancellation
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
LTC2488
After power up, the device initiates an internal reset cycle
which sets the input channel to CH0 to CH1 (IN
CH1). The fi rst conversion automatically begins at power
up using this default input channel. Once the conversion is
complete, a new word may be written into the device.
The fi rst three bits of the input word consist of two pre-
amble bits and one enable bit. These three bits are used
to enable the 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 remains 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).
The fi rst input bit (SGL) following the 101 sequence
determines if the input selection is differential (SGL =
14
Table 4. Serial Interface Timing Modes
CONFIGURATION
External SCK, Single Cycle
Conversion
External SCK, 3-Wire I/O
Internal SCK, Single Cycle
Conversion
Internal SCK, 3-Wire I/O,
Continuous Conversion
Table 3 Channel Selection
*Default at power up
SGL
*0
0
0
0
1
1
1
1
ODD/
SIGN
0
0
1
1
0
0
1
1
MUX ADDRESS
A2
+
0
0
0
0
0
0
0
0
SOURCE
External
External
= CH0, IN
Internal
Internal
SCK
A1
0
0
0
0
0
0
0
0
CYCLE CONTROL
–
CONVERSION
A0
⎯ C ⎯ S and SCK
=
0
1
0
1
0
1
0
1
Continuous
⎯ C ⎯ S ↓
SCK
IN
IN
IN
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).
SERIAL INTERFACE TIMING MODES
The LTC2488’s 4-wire interface is SPI and MICROWIRE
compatible. This interface offers several fl exible modes
of operation. These include internal/external serial clock,
3- or 4-wire I/O, single cycle or continuous conversion. The
following sections describe each of these timing modes
in detail. In all cases, the converter can use the internal
oscillator (F
to the F
input format, data output format, and performance remain
the same. Refer to Table 4 for a summary.
0
+
–
+
CHANNEL SELECTION
IN
IN
IN
1
–
+
+
DATA OUTPUT
O
⎯ C ⎯ S and SCK
CONTROL
pin. For each mode, the operating cycle, data
Internal
IN
IN
IN
SCK
⎯ C ⎯ S ↓
2
O
+
–
+
= LOW) or an external oscillator connected
IN
IN
IN
3
–
+
+
CONNECTION AND
COM
IN
IN
IN
IN
WAVEFORMS
Figures 4, 5
Figures 7, 8
–
–
–
–
Figure 6
Figure 9
2488f