LTC2430IGN datasheet(31/40 Pages) LINER

31 / 40 page

LTC2430/LTC2431

24301f

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 VREF = 5V, the

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.

APPLICATIO S I FOR ATIO

INPUT SIGNAL FREQUENCY (Hz)

2431 F32

–10

–20

–30

–40

–50

–60

–70

–80

–90

–100

–110

–120

2fN 3fN 4fN 5fN 6fN 7fN 8fN

Figure 32. Input Normal Mode Rejection

INPUT SIGNAL FREQUENCY (Hz)

250fN 252fN 254fN 256fN 258fN 260fN 262fN

2431 F33

–10

–20

–30

–40

–50

–60

–70

–80

–90

–100

–110

–120

Figure 33. Input Normal Mode Rejection

INPUT FREQUENCY (Hz)

15 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240

2431 F34

–20

–40

–60

–80

–100

–120

VCC = 5V

VREF = 5V

VINCM = 2.5V

VIN(P-P) = 5V

FO = GND

TA = 25°C

MEASURED DATA

CALCULATED DATA

Figure 34. Input Normal Mode Rejection vs Input Frequency

Figure 35. Input Normal Mode Rejection vs Input Frequency

INPUT FREQUENCY (Hz)

100

125

150

175

200

2431 F35

–20

–40

–60

–80

–100

–120

VCC = 5V

VREF = 5V

VINCM = 2.5V

VIN(P-P) = 5V

FO = 5V

TA = 25°C

MEASURED DATA

CALCULATED DATA

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