Datasheet

LTC2480
31
2480fd
applicaTions inForMaTion
V
REF
translates into about 2.18 • 10
–6
• f
EOSC
ppm addi-
tional INL error. Figure 19 shows the typical INL error due
to the source resistance driving the V
REF
pin when large
C
REF
values are used. The user is advised to minimize the
source impedance driving the V
REF
pin.
In applications where the reference and input common
mode voltages are different, extra errors are introduced.
For every 1V of the reference and input common mode
voltage difference (V
REFCM
– V
INCM
) and a 5V reference,
each Ohm of reference source resistance introduces an
extra (V
REFCM
– V
INCM
)/(V
REF
• R
EQ
) full-scale gain error,
which is 0.074ppm when using internal oscillator and 60Hz
mode. When using internal oscillator and 50Hz/60Hz mode,
the extra full-scale gain error is 0.067ppm. When using
R
SOURCE
(Ω)
0
+FS ERROR (ppm)
50
70
90
10k
2480 F15
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
Figure 15. +FS Error vs R
SOURCE
at V
REF
(Small C
REF
)
Figure 16. –FS Error vs R
SOURCE
at V
REF
(Small C
REF
)
Figure 17. +FS Error vs R
SOURCE
at V
REF
(Large C
REF
)
R
SOURCE
(Ω)
0
–FS ERROR (ppm)
–30
–10
10
10k
2480 F16
–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
2480 F17
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
Figure 18. –FS Error vs R
SOURCE
at V
REF
(Large C
REF
)
Figure 19. INL vs Differential Input Voltage and
Reference Source Resistance for C
REF
> 1µF
R
SOURCE
(Ω)
0
–FS ERROR (ppm)
–200
–100
0
800
2480 F18
–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
2480 F19
–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