LTC2410IGN datasheet(30/44 Pages) LINER

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LTC2410

APPLICATIO S I FOR ATIO

front of the LTC2410, the input dynamic current should be

considered (see Input Current section). In cases where

large effective RC time constants are used, an external

buffer amplifier may be required to minimize the effects of

dynamic input current.

Traditional high order delta-sigma modulators, while pro-

viding very good linearity and resolution, suffer from po-

tential instabilities at large input signal levels. The propri-

etary architecture used for the LTC2410 third order modu-

lator 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 signals superimposed

over volt level perturbations and LTC2410 is eminently

suited for such tasks. When the perturbation is differential,

the specification of interest is the normal mode rejection

for large input signal levels. With a reference voltage

VREF = 5V, the LTC2410 has a full-scale differential input

range of 5V peak-to-peak. Figures 42 and 43 show mea-

surement results for the LTC2410 normal mode rejection

ratio with a 7.5V peak-to-peak (150% of full scale) input

signal superimposed over the more traditional normal mode

rejection ratio results obtained with a 5V peak-to-peak (full

scale) input signal. In Figure 42, the LTC2410 uses the

internal oscillator with the notch set at 60Hz (FO = LOW)

and in Figure 43 it uses the internal oscillator with the

notch set at 50Hz (FO = HIGH). It is clear that the LTC2410

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 42. Measured Input Normal Mode Rejection vs Input Frequency

Figure 43. Measured Input Normal Mode Rejection vs Input Frequency

INPUT FREQUENCY (Hz)

105 120 135 150 165 180 195 210 225 240

2410 F3a

–20

–40

–60

–80

–100

–120

VCC = 5V

REF+ = 5V

REF – = GND

VINCM = 2.5V

FO = GND

TA = 25°C

VIN(P-P) = 5V

VIN(P-P) = 7.5V

(150% OF FULL SCALE)

INPUT FREQUENCY (Hz)

2410 F4a

–20

–40

–60

–80

–100

–120

VCC = 5V

REF+ = 5V

REF – = GND

VINCM = 2.5V

FO = 5V

TA = 25°C

VIN(P-P) = 5V

VIN(P-P) = 7.5V

(150% OF FULL SCALE)

12.5

37.5

62.5

87.5 100 112.5 125 137.5 150 162.5 175 187.5 200

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