LTC2498 Linear Technology, LTC2498 Datasheet - Page 30

• Manufacturer Part Number: LTC2498
• Description: 24-Bit 8-/16-Channel ADC
• Manufacturer: Linear Technology

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APPLICATIONS INFORMATION
LTC2498
30
Figure 18. INL vs Differential Input Voltage and Reference
Source Resistance for C
Figure 16. +FS Error vs R
Figure 17. –FS Error vs R
–100
–400
–200
–300
–500
100
–10
500
400
300
200
10
–2
–4
–6
–8
8
6
4
2
0
0
0
–0.5
0
0
V
V
V
T
C
V
V
V
V
F
T
V
V
V
V
F
T
CC
REF
IN(CM)
A
REF
O
A
CC
REF
IN
IN
O
A
CC
REF
IN
IN
= 25°C
= GND
= 25°C
+
–
= GND
= 25°C
+
–
= 5V
= 5V
C
= 5V
= 3.75V
= 1.25V
= 5V
= 10μF
= 1.25V
= 3.75V
= 5V
= 5V
REF
–0.3
200
200
= 2.5V
= 1μF , 10μF
–0.1
REF
400
R
V
400
R
SOURCE
IN
SOURCE
/V
> 1μF
SOURCE
SOURCE
REF
C
REF
600
0.1
(V)
(Ω)
600
(Ω)
= 1μF , 10μF
C
R = 500Ω
C
R = 100Ω
at V
at V
REF
REF
C
C
R = 1k
REF
REF
800
0.3
800
= 0.01μF
= 0.01μF
REF
REF
= 0.1μF
= 0.1μF
2498 F18
2498 F16
2498 F17
(Large C
(Large C
1000
1000
0.5
REF
REF
)
)
The SINC
rejection at all frequencies except DC and integer multiples
of the modulator sampling frequency (f
and 20. The modulator sampling frequency is f
15,360Hz while operating with its internal oscillator and
f
of frequency F
When using the internal oscillator, the LTC2498 is designed
to reject line frequencies. As shown in Figure 21, rejec-
tion nulls occur at multiples of frequency f
determined by the input control bits FA and FB (f
or 60Hz or 55Hz for simultaneous rejection). Multiples of
the modulator sampling rate (f
S
= F
Figure 19. Input Normal Mode Rejection, Internal Oscillator
and 50Hz Rejection Mode
Figure 20. Input Normal Mode Rejection, Internal Oscillator
and 60Hz Rejection Mode
EOSC
–100
–110
–120
–100
–110
–120
4
–10
–20
–30
–40
–50
–60
–70
–80
–90
–10
–20
–30
–40
–50
–60
–70
–80
–90
/20 when operating with an external oscillator
digital fi lter provides excellent normal mode
0
0
0
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
0 f
DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)
EOSC
f
S
S
2f
2f
S
.
S
3f
S
3f
4f
S
S
4f
5f
S
S
5f
6f
S
S
S
7f
6f
= f
S
S
8f
N
7f
S
S
• 256) only reject noise
9f
S
8f
10f
S
S
S
9f
11f
2498 F20
2498 F19
), see Figures 19
S
S
10f
12f
N
S
S
, where f
N
= 50Hz
2498fc
S
N
is
=