
LTC2494
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
rejectionoflinefrequenciesremainsunchanged,thusfully
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 fEOSC 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 fEOSC =
307.2kHz) is reduced, proportionally.
Once the external oscillator frequency is increased above
1MHz(amorethan3xincreaseinoutputrate)theeffective-
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
VCC = 5V
VREF = 5V
VIN(CM) = 2.5V
TA = 25°C
VIN(P-P) = 5V
VIN(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
VCC = 5V
VREF = 5V
VIN(CM) = 2.5V
TA = 25°C
VIN(P-P) = 5V
VIN(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 (fN)
INPUT
NORMAL
REJECTION
(dB)
2494 F28
0
–20
–40
–60
–80
–100
–120
0
fN 2fN 3fN 4fN 5fN 6fN 7fN 8fN
INPUT SIGNAL FREQUENCY (fN)
INPUT
NORMAL
REJECTION
(dB)
2494 F29
0
–20
–40
–60
–80
–100
–120
250
248
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