Datasheet

LTC2494
31
2494fd
applications inForMation
100pF up to 10k will not degrade the performance) (see
Figures 14, 15).
In cases where large bypass capacitors are required
on the reference inputs (C
REF
> 0.01µF) full-scale and
linearity errors are proportional to the value of the refer-
ence resistance. Every ohm of reference resistance pro-
duces a full-scale error of approximately 0.5ppm (while
operating in simultaneous 50Hz/60Hz mode) (see Figures
16 and 17). If the input common mode voltage is equal to
the reference common mode voltage, a linearity error of
approximately 0.67ppm per 100Ω of reference resistance
results (see Figure 18). In applications where the input
and reference common mode voltages are different, the
errors increase. A 1V difference in between common mode
input and common mode reference results in a 6.7ppm
INL error for every 100Ω of reference resistance.
Figure 16. +FS Error vs R
SOURCE
at V
REF
(Large C
REF
)
Figure 17. –FS Error vs R
SOURCE
at V
REF
(Large C
REF
)
Figure 18. INL vs Differential Input Voltage and
Reference Source Resistance for C
REF
> 1µF
Figure 14. +FS Error vs R
SOURCE
at V
REF
(Small C
REF
)
Figure 15. –FS Error vs R
SOURCE
at V
REF
(Small C
REF
)
R
SOURCE
(Ω)
0
+FS ERROR (ppm)
50
70
90
10k
2494 F14
30
10
40
60
80
20
0
–10
10
100
1k
100k
V
CC
= 5V
V
REF
= 5V
V
IN
+
= 3.75V
V
IN
–
= 1.25V
f
O
= GND
T
A
= 25°C
C
REF
= 0.01µF
C
REF
= 0.001µF
C
REF
= 100pF
C
REF
= 0pF
R
SOURCE
(Ω)
0
–FS ERROR (ppm)
–30
–10
10
10k
2494 F15
–50
–70
–40
–20
0
–60
–80
–90
10
100
1k
100k
V
CC
= 5V
V
REF
= 5V
V
IN
+
= 1.25V
V
IN
–
= 3.75V
f
O
= GND
T
A
= 25°C
C
REF
= 0.01µF
C
REF
= 0.001µF
C
REF
= 100pF
C
REF
= 0pF
R
SOURCE
(Ω)
0
+FS ERROR (ppm)
300
400
500
800
2494 F16
200
100
0
200
400
600
1000
V
CC
= 5V
V
REF
= 5V
V
IN
+
= 3.75V
V
IN
–
= 1.25V
f
O
= GND
T
A
= 25°C
C
REF
= 1µF, 10µF
C
REF
= 0.1µF
C
REF
= 0.01µF
R
SOURCE
(Ω)
0
–FS ERROR (ppm)
–200
–100
0
800
2494 F17
–300
–400
–500
200
400
600
1000
V
CC
= 5V
V
REF
= 5V
V
IN
+
= 1.25V
V
IN
–
= 3.75V
f
O
= GND
T
A
= 25°C
C
REF
= 1µF, 10µF
C
REF
= 0.1µF
C
REF
= 0.01µF
V
IN
/V
REF
(V)
–0.5
INL (ppm OF V
REF
)
2
6
10
0.3
2494 F18
–2
–6
0
4
8
–4
–8
–10
–0.3
–0.1
0.1
0.5
V
CC
= 5V
V
REF
= 5V
V
IN(CM)
= 2.5V
T
A
= 25°C
C
REF
= 10µF
R = 1k
R = 100Ω
R = 500Ω