LTC2497 Linear Technology, LTC2497 Datasheet - Page 23

• Manufacturer Part Number: LTC2497
• Description: 16-Bit 8-/16-Channel ADC
• Manufacturer: Linear Technology

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APPLICATIONS INFORMATION
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 (while operat-
ing with the internal oscillator) (see Figures 13 and 14). If
the input common mode voltage is equal to the reference
common mode voltage, a linearity error of approximately
0.67ppm per 100Ω of reference resistance results (see
Figure 15). 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 100Ω of reference resistance.
Figure 13. +FS Error vs R
500
400
100
300
200
0
0
V
V
V
V
F
T
O
A
CC
REF
IN
IN
= GND
= 25°C
+
–
= 5V
= 3.75V
= 1.25V
= 5V
200
REF
400
R
> .01µF), full-scale and linear-
SOURCE
SOURCE
C
REF
600
(Ω)
= 1µF, 10µF
at V
C
REF
C
REF
REF
800
Figure 15. INL vs Differential Input Voltage and
Reference Source Resistance for C
= 0.01µF
= 0.1µF
(Large C
–10
2497 F13
10
–2
–4
–6
–8
8
6
4
2
0
– 0.5
1000
V
V
V
T
C
A
CC
REF
IN(CM)
REF
= 25°C
= 5V
REF
= 5V
= 10µF
– 0.3
= 2.5V
)
– 0.1
V
IN
/V
REF
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 100Ω reference
resistance will create a 0.5µV full-scale error.
Normal Mode Rejection and Antialiasing
One of the advantages delta-sigma ADCs offer over
conventional ADCs is on-chip digital fi ltering. Combined
with a large oversample ratio, the LTC2497 signifi cantly
simplifi es antialiasing fi lter requirements. Additionally,
the input current cancellation feature allows external low
pass fi ltering without degrading the DC performance of
the device.
0.1
R = 500Ω
R = 100Ω
R = 1k
Figure 14. –FS Error vs R
0.3
REF
2497 F15
> 1µF
–100
–300
–400
–500
–200
0.5
0
0
V
V
V
V
F
T
O
A
CC
REF
IN
IN
= GND
= 25°C
C
+
–
= 5V
REF
= 1.25V
= 3.75V
= 5V
200
= 1µF, 10µF
400
R
SOURCE
SOURCE
600
(Ω)
at V
C
REF
C
REF
REF
800
= 0.01µF
LTC2497
= 0.1µF
(Large C
2497 F14
1000
REF
23
)
2497f