LTC2492 Linear Technology, LTC2492 Datasheet - Page 29

• Manufacturer Part Number: LTC2492
• Description: 24-Bit 2-/4-Channel ADC
• Manufacturer: Linear Technology

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APPLICATIONS INFORMATION
In cases where large bypass capacitors are required on
the reference inputs (C
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 operating
in simultaneous 50Hz/60Hz mode) (see Figures 15 and 16).
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 17). In applications where the input and reference
Figure 15. +FS Error vs R
Figure 16. –FS Error vs R
–400
–300
–500
–100
–200
500
400
200
100
300
0
0
0
0
V
V
V
V
F
T
V
V
V
V
F
T
O
O
A
CC
REF
IN
IN
A
CC
REF
IN
IN
= GND
= 25°C
= GND
= 25°C
+
–
+
–
C
= 5V
= 5V
REF
= 1.25V
= 3.75V
= 3.75V
= 1.25V
= 5V
= 5V
200
200
= 1μF, 10μF
REF
400
> 0.01μF) full-scale and linearity
R
400
R
SOURCE
SOURCE
SOURCE
SOURCE
C
REF
600
(Ω)
600
(Ω)
= 1μF, 10μF
at V
at V
C
C
REF
REF
C
C
REF
REF
REF
REF
800
800
= 0.01μF
= 0.01μF
= 0.1μF
= 0.1μF
(Large C
(Large C
2492 F15
2492 F16
1000
1000
REF
REF
)
)
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.
In addition to the reference sampling charge, the reference
ESD protection diodes have a temperature dependent
leakage 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 Anti-aliasing
One of the advantages delta-sigma ADCs offer over
conventional ADCs is on-chip digital fi ltering. Combined
with a large oversample ratio, the LTC2492 signifi cantly
simplifi es anti-aliasing fi lter requirements. Additionally,
the input current cancellation feature allows external low
pass fi ltering without degrading the DC performance of
the device.
Figure 17. INL vs Differential Input Voltage and Reference
Source Resistance for C
–10
–2
–4
–6
–8
10
8
6
4
2
0
–0.5
V
V
V
T
C
A
CC
REF
IN(CM)
REF
= 25°C
= 5V
= 5V
= 10μF
–0.3
= 2.5V
REF
–0.1
V
> 1μF
IN
/V
REF
0.1
R = 500Ω
R = 100Ω
R = 1k
0.3
LTC2492
2492 F17
0.5
29
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