LT1461 LINER [Linear Technology], LT1461 Datasheet - Page 12

• Manufacturer Part Number: LT1461
• Description: Easy-to-Use, Ultra-Tiny, Differential, 16-Bit ADC With I2C Interface
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
LTC2453
2) The bandwidth from V
3) Switching transients generated by the ADC are attenu-
4) A large C
5) Increasing R
There is a limit to how large R
application. Increasing R
the voltage drop across R
to the point that signifi cant measurement errors exist.
Additionally, for some applications, increasing the R
product too much may unacceptably attenuate the signal
at frequencies of interest.
For most applications, it is desirable to implement C
a high-quality 0.1μF ceramic capacitor and R
capacitor should be located as close as possible to the
actual V
by this circuit path, as well as the path length, should be
minimized.
In the case of a 2-wire sensor that is not remotely
grounded, it is desirable to split R
resistors in the ADC input line as well as in the sensor
12
(IN
from high frequency signals, and as such provides
simple antialiasing and input noise reduction.
ated before they go back to the signal source.
helping reduce refl ections back to the signal source.
during an outside-the-rails fault condition.
+
, IN
IN
Figure 10. Measured INL vs Input Voltage,
C
package pin. Furthermore, the area encompassed
–
–10
IN
10
–2
–4
–6
–8
). This bandwidth reduction isolates the ADC
IN
8
6
4
2
0
= 0.1μF, V
–5
gives a better AC ground at the input pins,
C
V
T
A
S
IN
CC
R
–4
= 25°C
S
= 0.1μF
protects the ADC by limiting the current
= 5V
DIFFERENTIAL INPUT VOLTAGE (V)
= 1k
–3
R
S
CC
–2
= 2k
R
= 5V, T
S
S
–1
R
= 0
SIG
S
beyond a given point increases
= 10k
S
0
is reduced at the input pins
S
A
due to the input current,
• C
1
= 25°C
IN
2
should be for a given
S
3
and place series
4
2453 F10
5
S
≤ 1k. This
S
IN
• C
as
IN
ground return line, which should be tied to the ADC GND
pin using a star connection topology.
Figure 10 shows the measured LTC2453 INL vs Input
Voltage as a function of R
C
In some cases, R
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 τ = R
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/(2πR
Finally, if the recommended choice for C
for the user’s specifi c application, an alternate strategy is to
eliminate C
this confi guration 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
measurements of Figure 11 include a capacitor C
responding to a minimum sized layout pad and a minimum
width input trace of about 1 inch length.
IN
= 0.1μF.
Figure 11. Measured INL vs Input Voltage,
C
IN
IN
–10
10
–2
–4
–6
–8
S
8
6
4
2
0
= 0, V
and minimize C
–5
• C
C
V
T
A
IN
CC
S
–4
IN
= 25°C
= 0
= 5V
can be increased above these guidelines.
R
DIFFERENTIAL INPUT VOLTAGE (V)
CC
, is of the same order of magnitude or
S
R
–3
R
S
= 1k, 2k
= 5V, T
S
= 10k
= 0
–2
–1
S
A
IN
= 25°C
value with an input capacitor
PAR
0
is shown in Figure 11. The
and R
1
2
S
3
. In practical terms,
IN
4
2453 F11
is unacceptable
5
S
PAR
C
IN
).
cor-
2453f