Datasheet
LTC2484
29
2484fd
APPLICATIONS INFORMATION
in 1.67 • 10
–6
• f
EOSC
ppm gain error. The typical +FS and
–FS errors for various combinations of source resistance
seen by the V
REF
pin and external capacitance connected
to that pin are shown in Figures 15-18.
In addition to this gain error, the converter INL per-
formance is degraded by the reference source imped-
ance. The INL is caused by the input dependent terms
–V
IN
2
/(V
REF
• R
EQ
) – (0.5 • V
REF
• D
T
)/R
EQ
in the reference
pin current as expressed in Figure 11. When using internal
oscillator and 60Hz mode, every 100Ω of reference source
resistance translates into about 0.67ppm additional INL
error. When using internal oscillator and 50Hz/60Hz mode,
every 100Ω of reference source resistance translates into
about 0.61ppm additional INL error. When using internal
oscillator and 50Hz mode, every 100Ω of reference source
resistance translates into about 0.56ppm additional INL
error. When f
O
is driven by an external oscillator with a
frequency f
EOSC
, every 100Ω of source resistance driving
R
SOURCE
(Ω)
0
+FS ERROR (ppm)
50
70
90
10k
2484 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
)
R
SOURCE
(Ω)
0
–FS ERROR (ppm)
–30
–10
10
10k
2484 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
Figure 16. –FS Error vs R
SOURCE
at V
REF
(Small C
REF
)
R
SOURCE
(Ω)
0
+FS ERROR (ppm)
300
400
500
800
2484 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 17. +FS Error vs R
SOURCE
at V
REF
(Large C
REF
)
Figure 18. –FS Error vs R
SOURCE
at V
REF
(Large C
REF
)
R
SOURCE
(Ω)
0
–FS ERROR (ppm)
–200
–100
0
800
2484 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