ltc2493 Linear Technology Corporation, ltc2493 Datasheet - Page 24

• Manufacturer Part Number: ltc2493
• Description: 24-bit 2-/4-channel Delta Sigma Adc With Easy Drive Input Current Cancellation And I2c Interface
• Manufacturer: Linear Technology Corporation

LTC2493
applicaTions inForMaTion
Reference Current
Similar to the analog inputs, the LTC2493 samples the
differential reference pins (REF
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
Figure 12. +FS Error vs R
Figure 14. +FS Error vs R
< 1nF), the voltage on the sampling capacitor settles
–10
500
400
200
100
300
90
80
70
60
50
40
30
20
10
0
0
0
0
V
V
V
V
F
T
V
V
V
V
F
T
O
A
CC
REF
IN
IN
O
CC
REF
IN
IN
A
= GND
= 25°C
+
–
= GND
= 25°C
+
–
= 5V
= 5V
= 3.75V
= 1.25V
= 5V
= 3.75V
= 1.25V
C
= 5V
200
C
REF
10
C
REF
REF
C
= 0.001µF
REF
= 0.01µF
= 100pF
= 0pF
100
R
400
R
SOURCE
SOURCE
SOURCE
SOURCE
C
REF
+
(Ω)
600
(Ω)
1k
= 1µF, 10µF
and REF
at V
at V
C
REF
C
REF
REF
REF
10k
800
= 0.01µF
= 0.1µF
(Small C
(Large C
2493 F12
2493 F14
–
) transferring
100k
1000
REF
REF
)
)
for reference impedances of many kW
to 10kW will not degrade the performance (see Figures
12 and 13)
In cases where large bypass capacitors are required on
the reference inputs (C
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
ing in simultaneous 50Hz/60Hz mode (see Figures 14
and 15)
Figure 13. –FS Error vs R
Figure 15. –FS Error vs R
)
. If the input common mode voltage is equal to
–100
–200
–300
–400
–500
–10
–20
–30
–40
–50
–60
–70
–80
–90
)
10
.
0
0
0
0
V
V
V
V
F
T
V
V
V
V
F
T
O
CC
REF
IN
IN
A
O
CC
REF
IN
IN
A
= GND
= 25°C
+
–
C
= GND
= 25°C
+
–
C
= 5V
= 5V
REF
= 1.25V
= 3.75V
= 1.25V
= 3.75V
C
= 5V
REF
= 5V
C
REF
200
10
REF
C
= 1µF, 10µF
= 0.001µF
REF
= 0.01µF
= 100pF
REF
= 0pF
100
R
400
R
SOURCE
SOURCE
> .01µF), full-scale and linear-
SOURCE
SOURCE
(Ω)
600
(Ω)
1k
C
at V
at V
REF
C
REF
10k
800
= 0.01µF
REF
REF
(
= 0.1µF
if C
2493 F13
(Small C
2493 F15
(Large C
REF
100k
1000
(
while operat-
= 100pF up
REF
REF
)
)
2493fa