Datasheet
LTC2452
16
2452fd
For more information www.linear.com/LTC2452
applicaTions inForMaTion
In the case of a 2-wire sensor that is not remotely
grounded, it is desirable to split R
S
and place series
resistors in the ADC input line as well as in the sensor
ground
return line, which should be tied to the ADC GND
pin using a star connection topology.
Figure 17 shows the measured LTC2452 INL vs Input
Voltage as a function of R
S
value with an input capacitor
C
IN
= 0.1µF.
In some cases, R
S
can be increased above these guidelines.
The input current is zero when the ADC is either in sleep
or I/O modes. Thus, if the time constant of the input RC
circuit t = R
S
• C
IN
, is of the same order of magnitude or
longer than the time periods between actual conversions,
then one can consider the input current to be reduced
correspondingly.
These considerations need to be balanced out by the input
signal bandwidth. The 3dB bandwidth ≈ 1/(2pR
S
C
IN
).
Finally, if the recommended choice for C
IN
is unacceptable
for the user’s specific application, an alternate strategy is to
eliminate C
IN
and minimize C
PAR
and R
S
. In practical terms,
this configuration corresponds to a low impedance sensor
directly
connected to the ADC through minimum length
traces. Actual applications include current measurements
through low value sense resistors, temperature measure
-
ments, low impedance voltage source monitoring, and so
on.
The resultant INL vs V
IN
is shown in Figure 18. The
measurements of Figure 18 include a capacitor C
PAR
cor-
responding to
a minimum sized layout pad and a minimum
width input trace of about 1 inch length.
Figure 17. Measured INL vs Input Voltage,
C
IN
= 0.1µF, V
CC
= 5V, T
A
= 25°C
Figure 18. Measured INL vs Input Voltage,
C
IN
= 0, V
CC
= 5V, T
A
= 25°C
DIFFERENTIAL INPUT VOLTAGE (V)
–5
INL (LSB)
2
6
10
3
2452 F17
–2
–6
0
4
8
–4
–8
–10
–3–4
–1–2
1 2 4
0
5
R
S
= 10k
R
S
= 2k
R
S
= 1k
R
S
= 0
C
IN
= 0.1µF
V
CC
= 5V
T
A
= 25°C
DIFFERENTIAL INPUT VOLTAGE (V)
–5
INL (LSB)
2
6
10
3
2452 F18
–2
–6
0
4
8
–4
–8
–10
–3–4
–1–2
1 2 4
0
5
R
S
= 10k
R
S
= 1k, 2k
R
S
= 0
C
IN
= 0
V
CC
= 5V
T
A
= 25°C