
LTC2498
34
2498ff
applications inForMation
mode rejection of line frequencies. The common mode
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.
Figure 30. Input Normal Mode Rejection
2x Speed Mode with and Without Running
Averaging
Figure 31. Offset Error vs Output Data
Rate and Temperature
Figure 32. +FS Error vs Output Data
Rate and Temperature
Figure 33.–FS Error vs Output Data Rate
and Temperature
Figure 34. Resolution (NoiseRMS ≤ 1LSB)
vs Output Data Rate and Temperature
Figure 35. Resolution (INLMAX ≤ 1LSB)
vs Output Data Rate and Temperature
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
48
–70
–80
–90
–100
–110
–120
–130
–140
54
58
2498 F30
50
52
56
60
62
NORMAL
MODE
REJECTION
(dB)
NO AVERAGE
WITH
RUNNING
AVERAGE
OUTPUT DATA RATE (READINGS/SEC)
–10
OFFSET
ERROR
(ppm
OF
V
REF
)
10
30
50
0
20
40
20
40
60
80
2498 F31
100
10
0
30
50
70
90
VIN(CM) = VREF(CM)
VCC = VREF = 5V
VIN = 0V
fO = EXT CLOCK
TA = 85°C
TA = 25°C
OUTPUT DATA RATE (READINGS/SEC)
0
+FS
ERROR
(ppm
OF
V
REF
)
500
1500
2000
2500
3500
10
50
70
2498 F32
1000
3000
40
90 100
20 30
60
80
VIN(CM) = VREF(CM)
VCC = VREF = 5V
fO = EXT CLOCK
TA = 85°C
TA = 25°C
OUTPUT DATA RATE (READINGS/SEC)
0
–3500
–FS
ERROR
(ppm
OF
V
REF
)
–3000
–2000
–1500
–1000
0
10
50
70
2498 F33
–2500
–500
40
90 100
20 30
60
80
VIN(CM) = VREF(CM)
VCC = VREF = 5V
fO = EXT CLOCK
TA = 85°C
TA = 25°C
OUTPUT DATA RATE (READINGS/SEC)
0
10
RESOLUTION
(BITS)
12
16
18
20
24
10
50
70
2498 F34
14
22
40
90 100
20 30
60
80
VIN(CM) = VREF(CM)
VCC = VREF = 5V
VIN = 0V
fO = EXT CLOCK
RES = LOG 2 (VREF/NOISERMS)
TA = 85°C
TA = 25°C
OUTPUT DATA RATE (READINGS/SEC)
0
10
RESOLUTION
(BITS)
12
16
18
22
10
50
70
2498 F35
14
20
40
90 100
20 30
60
80
TA = 85°C
TA = 25°C
VIN(CM) = VREF(CM)
VCC = VREF = 5V
fO = EXT CLOCK
RES = LOG 2 (VREF/INLMAX)