LTC2431 Linear Technology, LTC2431 Datasheet - Page 31

• Manufacturer Part Number: LTC2431
• Description: (LTC2430 / LTC2431) 20-Bit No Latency Delta-Sigma ADCs
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
Traditional high order delta-sigma modulators, while pro-
viding very good linearity and resolution, suffer from
potential instabilities at large input signal levels. The pro-
prietary architecture used for the LTC2430/LTC2431 third
order modulator resolves this problem and guarantees a
predictable stable behavior at input signal levels of up to
150% of full scale. In many industrial applications, it is
not uncommon to have to measure microvolt level sig-
nals superimposed over volt level perturbations and
LTC2430/LTC2431 are eminently suited for such tasks.
When the perturbation is differential, the specification of
interest is the normal mode rejection for large input sig-
nal levels. With a reference voltage V
Figure 34. Input Normal Mode Rejection vs Input Frequency
–100
–120
–20
–40
– 60
–80
0
0
–100
–110
–120
–10
–20
–30
–40
–50
–60
–70
–80
–90
15 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240
Figure 32. Input Normal Mode Rejection
0
0
f
N
INPUT SIGNAL FREQUENCY (Hz)
U
2f
N
3f
INPUT FREQUENCY (Hz)
N
U
4f
N
MEASURED DATA
CALCULATED DATA
5f
N
6f
W
N
7f
N
2431 F32
8f
REF
N
V
V
V
V
F
T
O
A
CC
REF
INCM
IN(P-P)
U
= 5V, the
= GND
= 25 C
= 5V
= 5V
= 2.5V
2431 F34
= 5V
LTC2430/LTC2431 have a full-scale differential input range
of 5V peak-to-peak. Figures 36 and 37 show measure-
ment results for the LTC2430/LTC2431 normal mode re-
jection ratio with a 7.5V peak-to-peak (150% of full scale)
input signal superimposed over the more traditional nor-
mal mode rejection ratio results obtained with a 5V peak-
to-peak (full scale) input signal. It is clear that the LTC2430/
LTC2431 rejection performance is maintained with no
compromises in this extreme situation. When operating
with large input signal levels, the user must observe that
such signals do not violate the device absolute maximum
ratings.
Figure 35. Input Normal Mode Rejection vs Input Frequency
–100
–120
– 60
–20
–40
–80
0
0
–100
–110
–120
–10
–20
–30
–40
–50
–60
–70
–80
–90
Figure 33. Input Normal Mode Rejection
0
250f
25
N
252f
INPUT SIGNAL FREQUENCY (Hz)
50
N
LTC2430/LTC2431
254f
INPUT FREQUENCY (Hz)
N
75
256f
MEASURED DATA
CALCULATED DATA
N
100
258f
N
125
260f
N
2431 F33
150
262f
N
V
V
V
V
F
T
O
A
CC
REF
INCM
IN(P-P)
= 5V
= 25 C
175
= 5V
= 5V
= 2.5V
31
= 5V
2431 F35
200
24301f