LTC2497 Linear Technology, LTC2497 Datasheet - Page 25

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

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APPLICATIONS INFORMATION
by the user and can be made insignifi cantly short. When
operating with an external conversion clock (f
to an external oscillator), the LTC2497 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
late 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 effective resolution as well as a shift in frequency
rejection.
A change in f
internal notch position. This leads to reduced differential
mode rejection of line frequencies. The common mode
Figure 18. Input Normal Mode Rejection vs Input Frequency with
Input Perturbation of 100% (50Hz/60Hz Notch)
–100
–120
– 60
–20
–40
–80
0
0
EOSC
20
. If f
EOSC
40
EOSC
EOSC
results in a proportional change in the
60
over the nominal 307.2kHz will trans-
= 307.2kHz, the converter behaves
80
INPUT FREQUENCY (Hz)
100
120
MEASURED DATA
CALCULATED DATA
140
160
O
180
connected
V
V
V
V
T
A
CC
REF
IN(CM)
IN(P-P)
= 25°C
= 5V
200
= 5V
= 2.5V
= 5V
2497 F18
220
Figure 19. Measure Input Normal Mode Rejection vs Input
Frequency with Input Perturbation of 150% (60Hz Notch)
rejection of line frequencies remains unchanged, thus fully
differential input signals with a high degree of symmetry
on both the IN
frequency noise.
An increase in f
input and reference current. External RC networks will
continue to have zero differential input current, but the
time required for complete settling (580ns for f
307.2kHz) is reduced, proportionally.
Once the external oscillator frequency is increased above
1MHz (a more than 3X increase in output rate) the effective-
ness of internal auto calibration circuits begins to degrade.
This results in larger offset errors, full-scale errors, and
decreased resolution, as shown in Figures 20 to 27.
–100
–120
– 60
–20
–40
–80
0
0
15
30
45
+
EOSC
and IN
60
also increases the effective dynamic
75
–
90
INPUT FREQUENCY (Hz)
pins will continue to reject line
105 120 135 150 165 180 195 210 225 240
V
V
(150% OF FULL SCALE)
IN(P-P)
IN(P-P)
= 5V
= 7.5V
LTC2497
V
V
V
T
A
CC
REF
IN(CM)
= 25°C
25
= 5V
EOSC
= 5V
= 2.5V
2497 F19
2497f
=