Datasheet

LTC2493
24
2493fd
R
SOURCE
(Ω)
0
+FS ERROR (ppm)
50
70
90
10k
2493 F12
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
2493 F13
–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
2493 F14
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
2493 F15
–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
Reference Current
Similar to the analog inputs, the LTC2493 samples the
differential reference pins (REF
+
and REF
–
) transferring
small amounts of charge to and from these pins, thus
producing a dynamic reference current. If incomplete set-
tling occurs (as a function the reference source resistance
and reference bypass capacitance) linearity and gain errors
are introduced.
For relatively small values of external reference capacitance
(C
REF
< 1nF), the voltage on the sampling capacitor settles
for reference impedances of many kΩ
(if C
REF
= 100pF
up to 10k will not degrade the performance (see Figures
12 and 13)
).
In cases where large bypass capacitors are required on
the reference inputs (C
REF
> .01µF), full-scale and linear-
ity errors are proportional to the value of the reference
resistance. Every ohm of reference resistance produces
a full-scale error of approximately 0.5ppm
(while operat-
ing in simultaneous 50Hz/60Hz mode (see Figures 14
and 15)
). If the input common mode voltage is equal to
Figure 12. +FS Error vs R
SOURCE
at V
REF
(Small C
REF
) Figure 13. –FS Error vs R
SOURCE
at V
REF
(Small C
REF
)
Figure 14. +FS Error vs R
SOURCE
at V
REF
(Large C
REF
) Figure 15. –FS Error vs R
SOURCE
at V
REF
(Large C
REF
)
applicaTions inForMaTion