Datasheet

LTC2410
33
APPLICATIO S I FOR ATIO
WUU
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Figure 39. Input Normal Mode Rejection Figure 40. Input Normal Mode Rejection
Figure 41. Input Normal Mode Rejection vs Input Frequency
with Input Perturbation of 100% Full Scale (60Hz Notch)
Figure 42. Input Normal Mode Rejection vs Input Frequency
with Input Perturbation of 100% Full Scale (50Hz Notch)
INPUT SIGNAL FREQUENCY (Hz)
INPUT NORMAL MODE REJECTION (dB)
2410 F39
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
–120
f
N
0 2f
N
3f
N
4f
N
5f
N
6f
N
7f
N
8f
N
INPUT SIGNAL FREQUENCY (Hz)
250f
N
252f
N
254f
N
256f
N
258f
N
260f
N
262f
N
INPUT NORMAL MODE REJECTION (dB)
2410 F40
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
–120
INPUT FREQUENCY (Hz)
0
15 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240
NORMAL MODE REJECTION (dB)
2410 F41
0
–20
–40
–60
–80
–100
–120
V
CC
= 5V
REF
+
= 5V
REF
–
= GND
V
INCM
= 2.5V
V
IN(P-P)
= 5V
F
O
= GND
T
A
= 25°C
MEASURED DATA
CALCULATED DATA
INPUT FREQUENCY (Hz)
0
12.5 25 37.5 50 62.5 75 87.5 100 112.5 125 137.5 150 162.5 175 187.5 200
NORMAL MODE REJECTION (dB)
2410 F42
0
–20
–40
–60
–80
–100
–120
V
CC
= 5V
REF
+
= 5V
REF
–
= GND
V
INCM
= 2.5V
V
IN(P-P)
= 5V
F
O
= 5V
T
A
= 25°C
MEASURED DATA
CALCULATED DATA
The combined normal mode rejection performance is
shown in Figure␣ 37 for the internal oscillator with 50Hz
notch setting (F
O
= HIGH) and in Figure␣ 38 for the internal
oscillator with 60Hz notch setting (F
O
= LOW) and for the
external oscillator mode. The regions of low rejection
occurring at integer multiples of f
S
have a very narrow
bandwidth. Magnified details of the normal mode rejection
curves are shown in Figure␣ 39 (rejection near DC) and
Figure␣ 40 (rejection at f
S
= 256f
N
) where f
N
represents the
notch frequency. These curves have been derived for the
external oscillator mode but they can be used in all
operating modes by appropriately selecting the f
N
value.
The user can expect to achieve in practice this level of
performance using the internal oscillator as it is demon-
strated by Figures 41 and 42. Typical measured values of
the normal mode rejection of the LTC2410 operating with
an internal oscillator and a 60Hz notch setting are shown
in Figure 41 superimposed over the theoretical calculated
curve. Similarly, typical measured values of the normal
mode rejection of the LTC2410 operating with an internal
oscillator and a 50Hz notch setting are shown in Figure 42
superimposed over the theoretical calculated curve.
As a result of these remarkable normal mode specifica-
tions, minimal (if any) antialias filtering is required in front
of the LTC2410. If passive RC components are placed in
front of the LTC2410, the input dynamic current should be
considered (see Input Current section). In cases where
large effective RC time constants are used, an external
buffer amplifier may be required to minimize the effects of
dynamic input current.