LTC2487 Linear Technology, LTC2487 Datasheet - Page 24

• Manufacturer Part Number: LTC2487
• Description: 16-Bit 2-/4-Channel ADC
• Manufacturer: Linear Technology

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LTC2487
applicaTions inForMaTion
For relatively small values of external reference capacitance
(C
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)

REF
Figure 12. +FS Error vs R
< 1nF), the voltage on the sampling capacitor settles
)
. If the input common mode voltage is equal to
500
400
200
100
–10
300
)
90
80
70
60
50
40
30
20
10
0
.
0
0
0
V
V
V
V
F
T
Figure 14. +FS Error vs R
at V
V
V
V
V
F
T
O
A
O
CC
REF
IN
IN
CC
REF
IN
IN
A
= GND
= 25°C
= GND
+
–
= 25°C
+
–
= 5V
= 5V
= 3.75V
= 1.25V
= 3.75V
= 1.25V
= 5V
REF
= 5V
C
200
C
10
REF
C
REF
REF
C
(Large C
= 0.001µF
REF
= 0.01µF
REF
= 100pF
= 0pF
100
400
R
R
SOURCE
SOURCE
> 0.01µF), full-scale and linear-
SOURCE
C
REF
REF
600
(Ω)
(Ω)
1k
)
= 1µF, 10µF
C
at V
REF
C
REF
800
SOURCE
10k
= 0.01µF
REF
(
= 0.1µF
if C
2487 F14
2487 F12
(Small C
1000
100k
REF
(
while operat-
= 100pF up
REF
)
the reference common mode voltage, a linearity error of
approximately 0.67ppm per 100W of reference resistance
results (see Figure 16). In applications where the input
and reference common mode voltages are different, the
errors increase. A 1V difference in between common mode
input and common mode reference results in a 6.7ppm
INL error for every 100W of reference resistance.
In addition to the reference sampling charge, the reference
ESD protection diodes have a temperature dependent leak-
age current. This leakage current, nominally 1nA (±10nA
max) results in a small gain error. A 100W reference
resistance will create a 0.5µV full-scale error.
Figure 13. –FS Error vs R
–100
–300
–400
–500
–200
–10
–20
–30
–40
–50
–60
–70
–80
–90
10
0
0
0
0
Figure 15. –FS Error vs R
at V
V
V
V
V
F
T
V
V
V
V
F
T
O
A
CC
REF
IN
IN
O
A
CC
REF
IN
IN
= GND
= 25°C
+
–
= GND
= 25°C
C
+
–
C
= 5V
= 1.25V
= 3.75V
= 5V
C
REF
REF
REF
= 5V
= 1.25V
= 3.75V
= 5V
C
REF
200
10
REF
C
= 1µF, 10µF
= 0.001µF
REF
(Large C
= 0.01µF
= 100pF
= 0pF
100
R
400
R
SOURCE
SOURCE
SOURCE
REF
(Ω)
600
1k
(Ω)
)
C
at V
REF
C
REF
SOURCE
10k
800
= 0.01µF
REF
= 0.1µF
2487 F13
2487 F15
(Small C
100k
1000
REF
)
2487fa