Datasheet
LTC2494
34
2494fd
Figure 26. Measure Input Normal Mode Rejection vs Input
Frequency with Input Perturbation of 150% (60Hz Notch)
Figure 27. Measure Input Normal Mode Rejection vs Input
Frequency With input Perturbation of 150% (50Hz Notch)
Figure 28. Input Normal Mode Rejection 2x Speed Mode
Figure 29. Input Normal Mode Rejection 2x Speed Mode
applications inForMation
rejection of line frequencies remains unchanged, thus fully
differential input signals with a high degree of symmetry
on both the IN
+
and IN
–
pins will continue to reject line
frequency noise.
An increase in f
EOSC
also increases the effective dynamic
input and reference current. External RC networks will
continue to have zero differential input current, but the
time required for complete settling (580ns for f
EOSC
=
307.2kHz) is reduced, proportionally.
Once the external oscillator frequency is increased above
1MHz (a more than 3x increase in output rate) the effective-
ness of internal auto calibration circuits begins to degrade.
This results in larger offset errors, full-scale errors and
decreased resolution (see Figures 31 to 38).
INPUT FREQUENCY (Hz)
0 15 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240
NORMAL MODE REJECTION (dB)
2494 F26
0
–20
–40
–60
–80
–100
–120
V
CC
= 5V
V
REF
= 5V
V
IN(CM)
= 2.5V
T
A
= 25°C
V
IN(P-P)
= 5V
V
IN(P-P)
= 7.5V
(150% OF FULL SCALE)
INPUT FREQUENCY (Hz)
0
NORMAL MODE REJECTION (dB)
2494 F27
0
–20
–40
–60
–80
–100
–120
V
CC
= 5V
V
REF
= 5V
V
IN(CM)
= 2.5V
T
A
= 25°C
V
IN(P-P)
= 5V
V
IN(P-P)
= 7.5V
(150% OF FULL SCALE)
12.5 25 37.5 50 62.5 75 87.5 100 112.5 125 137.5 150 162.5 175 187.5 200
INPUT SIGNAL FREQUENCY (f
N
)
INPUT NORMAL REJECTION (dB)
2494 F28
0
–20
–40
–60
–80
–100
–120
0
f
N
2f
N
3f
N
4f
N
5f
N
6f
N
7f
N
8f
N
INPUT SIGNAL FREQUENCY (f
N
)
INPUT NORMAL REJECTION (dB)
2494 F29
0
–20
–40
–60
–80
–100
–120
250248 252 254 256 258 260 262 264
Figure 30. Input Normal Mode Rejection 2x Speed Mode
with and Without Running Averaging
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
48
–70
–80
–90
–100
–110
–120
–130
–140
54 58
2494 F30
50 52
56 60 62
NORMAL MODE REJECTION (dB)
NO AVERAGE
WITH
RUNNING
AVERAGE