Datasheet

LTC2485
25
2485fc
APPLICATIONS INFORMATION
In addition to the reference sampling charge, the refer-
ence pins ESD protection diodes have a temperature de-
pendent leakage current. This leakage current, nominally
1nA (±10nA max), results in a small gain error. A 100
source resistance will create a 0.05µV typical and 0.5µV
maximum full-scale error.
Output Data Rate
When using its internal oscillator, the LTC2485 produces up
to 7.5 samples per second (sps) with a notch frequency of
60Hz, 6.25sps with a notch frequency of 50Hz and 6.82sps
with the 50Hz/60Hz rejection mode. The actual output
data rate will depend upon the length of the sleep and
data output phases which are controlled by the user and
which can be made insignifi cantly short. When operated
Figure 16. +FS Error vs R
SOURCE
at REF
+
or REF
–
(Small C
REF
)
Figure 17. –FS Error vs R
SOURCE
at REF
+
or REF
–
(Small C
REF
) Figure 18. +FS Error vs R
SOURCE
at REF
+
or REF
–
(Large C
REF
)
Figure 19. –FS Error vs R
SOURCE
at REF
+
or REF
–
(Large C
REF
) Figure 20. INL vs DIFFERENTIAL Input Voltage
and Reference Source Resistance for C
REF
> 1μF
R
SOURCE
()
0
+FS ERROR (ppm)
50
70
90
10k
2485 F16
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
T
A
= 25°C
C
REF
= 0.01µF
C
REF
= 0.001µF
C
REF
= 100pF
C
REF
= 0pF
R
SOURCE
()
0
–FS ERROR (ppm)
–30
–10
10
10k
2485 F17
–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
T
A
= 25°C
C
REF
= 0.01µF
C
REF
= 0.001µF
C
REF
= 100pF
C
REF
= 0pF
R
SOURCE
()
0
+FS ERROR (ppm)
300
400
500
800
2485 F18
200
100
0
200
400
600
1000
V
CC
= 5V
V
REF
= 5V
V
IN
+
= 3.75V
V
IN
–
= 1.25V
T
A
= 25°C
C
REF
= 1µF, 10µF
C
REF
= 0.1µF
C
REF
= 0.01µF
R
SOURCE
()
0
–FS ERROR (ppm)
–200
–100
0
800
2485 F19
–300
–400
–500
200
400
600
1000
V
CC
= 5V
V
REF
= 5V
V
IN
+
= 1.25V
V
IN
–
= 3.75V
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
2485 F20
–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 = 100
R = 500