Linear Technology DC1337A - LTC2309: 12-bit, 8-channel SAR ADC with I²C I/F, req DC590 DC1337A DC1337A Fiche De Données
Codes de produits
DC1337A
LTC2309
2309fd
AppLICAtIOns InFORMAtIOn
CH0
CH1
CH2
CH3
CH4
CH5
CH6
CH7
CH1
CH2
CH3
CH4
CH5
CH6
CH7
COM (
–
)
8 Single-Ended
+
+
+
+
+
+
+
4 Differential
+
(
–
)
+
+
(
–
)
+
(
–
)
+
(
–
)
–
(
+
)
–
(
+
)
–
(
+
)
–
(
+
)
COM (
–
)
Combinations of Differential
and Single-Ended
+
+
+
+
+
+
–
–
–
{
{
{
{
{
{
2309 F01a
CH0
CH1
CH1
CH2
CH3
CH3
CH4
CH5
CH5
CH6
CH7
CH7
CH0
CH1
CH1
CH2
CH3
CH4
CH5
CH6
CH7
CH3
CH4
CH5
CH6
CH7
Table 1. Channel Configuration
S/D O/S S1 S0
0
1
2
3
4
5
6
7 COM
0
0
0
0
+
–
0
0
0
1
+
–
0
0
1
0
+
–
0
0
1
1
+
–
0
1
0
0
–
+
0
1
0
1
–
+
0
1
1
0
–
+
0
1
1
1
–
+
1
0
0
0
+
–
1
0
0
1
+
–
1
0
1
0
+
–
1
0
1
1
+
–
1
1
0
0
+
–
1
1
0
1
+
–
1
1
1
0
+
–
1
1
1
1
+
–
COM
(UNUSED)
COM (
–
)
1st Conversion
2nd Conversion
+
–
+
–
+
–
+
+
{
{
{
{
CH2
CH3
CH3
CH4
CH5
CH5
CH2
CH3
CH3
CH4
CH5
CH5
2328 F01b
COM
COM
REFCOMP/2
Unipolar Mode
Bipolar Mode
2328 F02
+–
Figure 1a. Example of MUX Configurations
Figure 1b. Changing the MUX Assignments “On the Fly”
Figure 2. Driving COM in Unipolar and Bipolar Modes
mode, the analog inputs draw only a small leakage cur-
rent. If the source impedance of the driving circuit is
low, the ADC inputs can be driven directly. Otherwise,
more acquisition time should be allowed for a source
with higher impedance.
Input Filtering
The noise and distortion of the input amplifier and
The noise and distortion of the input amplifier and
other circuitry must be considered since they will add
to the ADC noise and distortion. Therefore, noisy input
circuitry should be filtered prior to the analog inputs to
minimize noise. A simple 1-pole RC filter is sufficient
for many applications.
The analog inputs of the LTC2309 can be modeled as
The analog inputs of the LTC2309 can be modeled as
a 55pF capacitor (C
IN
) in series with a 100Ω resistor
(R
ON
), as shown in Figure 3a. C
IN
gets switched to the
selected input once during each conversion. Large filter
RC time constants will slow the settling of the inputs.
It is important that the overall RC time constants be
short enough to allow the analog inputs to completely
settle to 12-bit resolution within the acquisition time
(t
ACQ
) if DC accuracy is important.