Datasheet

LTC2487
27
2487fd
Figure 25. Measure Input Normal Mode Rejection vs Input
Frequency with Input Perturbation of 150% (50Hz Notch)
Figure 24. Measure Input Normal Mode Rejection vs Input
Frequency with Input Perturbation of 150% (60Hz Notch)
APPLICATIONS INFORMATION
Figure 23. Input Normal Mode Rejection vs Input Frequency with
Input Perturbation of 100% (50Hz/60Hz Notch)
shown superimposed over the theoretical values in all
three rejection modes.
Traditional high order delta-sigma modulators suffer from
potential instabilities at large input signal levels. The
proprietary architecture used for the LTC2487 third order
modulator resolves this problem and guarantees stability
with input signals 150% of full scale. In many industrial
applications, it is not uncommon to have microvolt level
signals superimposed over unwanted error sources with
several volts if peak-to-peak noise. Figures 24 and 25 show
measurement results for the rejection of a 7.5V peak-
to-peak noise source (150% of full scale) applied to the
LTC2487. These curves show that the rejection performance
is maintained even in extremely noisy environments.
Using the 2x speed mode of the LTC2487 alters the rejection
INPUT FREQUENCY (Hz)
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
NORMAL MODE REJECTION (dB)
2487 F23
0
–20
–40
–60
–80
–100
–120
V
CC
= 5V
V
REF
= 5V
V
IN(CM)
= 2.5V
V
IN(P-P)
= 5V
?T
A
= 25°C
MEASURED DATA
CALCULATED DATA
INPUT FREQUENCY (Hz)
0
15 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240
NORMAL MODE REJECTION (dB)
2487 F24
0
–20
–40
–60
–80
–100
–120
V
CC
= 5V
V
REF
= 5V
V
IN(CM)
= 2.5V
T
A
= 25°C
V
IN(P-P)
= 5V
V
IN(P-P)
= 7.5V
(150% OF FULL SCALE)
INPUT FREQUENCY (Hz)
0
NORMAL MODE REJECTION (dB)
2487 F25
0
–20
–40
–60
–80
–100
–120
V
CC
= 5V
V
REF
= 5V
V
IN(CM)
= 2.5V
T
A
= 25°C
V
IN(P-P)
= 5V
V
IN(P-P)
= 7.5V
(150% OF FULL SCALE)
12.5 25 37.5 50 62.5 75 87.5 100 112.5 125 137.5 150 162.5 175 187.5 200