Datasheet

LTC2498
34
2498ff
applications inForMation
mode rejection of line frequencies. The common mode
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.
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 (Noise
RMS
≤ 1LSB)
vs Output Data Rate and Temperature
Figure 35. Resolution (INL
MAX
≤ 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
100100 30 50 70 90
V
IN(CM)
= V
REF(CM)
V
CC
= V
REF
= 5V
V
IN
= 0V
f
O
= EXT CLOCK
T
A
= 85°C
T
A
= 25°C
OUTPUT DATA RATE (READINGS/SEC)
0
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
V
IN(CM)
= V
REF(CM)
V
CC
= V
REF
= 5V
f
O
= EXT CLOCK
T
A
= 85°C
T
A
= 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
V
IN(CM)
= V
REF(CM)
V
CC
= V
REF
= 5V
f
O
= EXT CLOCK
T
A
= 85°C
T
A
= 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
V
IN(CM)
= V
REF(CM)
V
CC
= V
REF
= 5V
V
IN
= 0V
f
O
= EXT CLOCK
RES = LOG 2 (V
REF
/NOISE
RMS
)
T
A
= 85°C
T
A
= 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
T
A
= 85°C
T
A
= 25°C
V
IN(CM)
= V
REF(CM)
V
CC
= V
REF
= 5V
f
O
= EXT CLOCK
RES = LOG 2 (V
REF
/INL
MAX
)