Datasheet
LTC2484
31
2484fd
APPLICATIONS INFORMATION
through the input and the reference pins. If large external
input and/or reference capacitors (C
IN
, C
REF
) are used,
the previous section provides formulae for evaluating the
effect of the source resistance upon the converter perfor-
mance for any value of f
EOSC
. If small external input and/
or reference capacitors (C
IN
, C
REF
) are used, the effect of
the external source resistance upon the LTC2484 typical
performance can be inferred from Figures 13, 14, 15 and
16 in which the horizontal axis is scaled by 307200/f
EOSC
.
Third, an increase in the frequency of the external oscillator
above 1MHz (a more than 3× increase in the output data
rate) will start to decrease the effectiveness of the internal
autocalibration circuits. This will result in a progressive
degradation in the converter accuracy and linearity. Typical
measured performance curves for output data rates up to
100 readings per second are shown in Figures 20 to 27. In
order to obtain the highest possible level of accuracy from
this converter at output data rates above 20 readings per
OUTPUT DATA RATE (READINGS/SEC)
–10
OFFSET ERROR (ppm OF V
REF
)
10
30
50
0
20
40
20 40 60 80
2484 F20
10010030507090
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
Figure 20. Offset Error vs Output Data Rate and Temperature
OUTPUT DATA RATE (READINGS/SEC)
0
0
+FS ERROR (ppm OF V
REF
)
500
1500
2000
2500
3500
10
50
70
2484 F21
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
Figure 21. +FS Error vs Output Data Rate and Temperature
Figure 22. –FS Error vs Output Data Rate and Temperature
OUTPUT DATA RATE (READINGS/SEC)
0
–3500
–FS ERROR (ppm OF V
REF
)
–3000
–2000
–1500
–1000
0
10
50
70
2484 F22
–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
2484 F23
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
Figure 23. Resolution (Noise
RMS
≤ 1LSB)
vs Output Data Rate and Temperature