LTC2498 Linear Technology, LTC2498 Datasheet - Page 32

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

www.DataSheet4U.com
APPLICATIONS INFORMATION
LTC2498
noise. Figures 26 and 27 show measurement results for
the rejection of a 7.5V peak-to-peak noise source (150%
of full scale) applied to the LTC2498. From these curves,
it is shown that the rejection performance is maintained
even in extremely noisy environments.
Using the 2x speed mode of the LTC2498 alters the rejec-
tion characteristics around DC and multiples of f
device bypasses the offset calibration in order to increase
the output rate. The resulting rejection plots are shown
in Figures 28 and 29. 1x type frequency rejection can be
achieved using the 2x mode by performing a running
average of the conversion results, see Figure 30.
Output Data Rate
When using its internal oscillator, the LTC2498 produces up
to 7.5 samples per second (sps) with a notch frequency of
60Hz. The actual output data rate depends upon the length
32
Figure 26. Measure Input Normal Mode Rejection vs Input
Frequency with Input Perturbation of 150% (60Hz Notch)
Figure 27. Measure Input Normal Mode Rejection vs Input
Frequency With input Perturbation of 150% (50Hz Notch)
–100
–120
–100
–120
–20
–40
–60
–80
–20
–40
–60
–80
0
0
0
0
12.5 25 37.5 50 62.5 75 87.5 100 112.5 125 137.5 150 162.5 175 187.5 200
15
30
45
60
75
90
INPUT FREQUENCY (Hz)
INPUT FREQUENCY (Hz)
105 120 135 150 165 180 195 210 225 240
V
V
(150% OF FULL SCALE)
V
V
(150% OF FULL SCALE)
IN(P-P)
IN(P-P)
IN(P-P)
IN(P-P)
= 5V
= 7.5V
= 5V
= 7.5V
V
V
V
T
V
V
V
T
A
A
CC
REF
IN(CM)
CC
REF
IN(CM)
= 25°C
= 25°C
= 5V
= 5V
= 5V
= 5V
S
= 2.5V
= 2.5V
. The
2498 F26
2498 F27
of the sleep and data output cycles which are controlled
by the user and can be made insignifi cantly short. When
operating with an external conversion clock (F
to an external oscillator), the LTC2498 output data rate
can be increased. The duration of the conversion cycle is
41036/f
as if the internal oscillator is used.
An increase in f
into a proportional increase in the maximum output data
rate (up to a maximum of 100sps). The increase in output
rate leads to degradation in offset, full-scale error, and ef-
fective resolution as well as a shift in frequency rejection.
When using the integrated temperature sensor, the internal
oscillator should be used (f
applied to f
A change in f
internal notch position. This leads to reduced differential
Figure 29. Input Normal Mode Rejection 2x Speed Mode
Figure 28. Input Normal Mode Rejection 2x Speed Mode
EOSC
O
. If f
, f
–100
–120
–100
–120
EOSC
–20
–40
–60
–80
–20
–40
–60
–80
EOSC
EOSC
0
0
248
0
EOSC
250
results in a proportional change in the
f
over the nominal 307.2kHz will translate
N
, should be set to 307.2kHz Max.
INPUT SIGNAL FREQUENCY (f
INPUT SIGNAL FREQUENCY (f
252 254 256 258 260 262 264
2f
= 307.2kHz, the converter behaves
N
3f
N
O
4f
N
= 0) or an external oscillator
5f
N
6f
N
N
N
)
)
7f
N
2498 F29
2498 F28
8f
N
O
connected
2498fc