LTC2415-1IGN datasheet(32/40 Pages) LINER

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LTC2415/LTC2415-1

sn2415 24151fs

APPLICATIO S I FOR ATIO

FREQUENCY AT VIN (Hz)

–120

–100

–80

–60

–40

–20

100

150

200

2415 F30

250

VCC = 5V

VREF = 5V

VIN = 2.5V

FO = 0

INPUT FREQUENCY

–60

–40

2415 F31

–80

–100

fS/2

–120

–140

–20

INPUT FREQUENCY DEVIATION FROM NOTCH FREQUENCY (%)

–12

–8

–4

048

2415 F32

–60

–70

–80

–90

–100

–110

–120

–130

–140

DIFFERENTIAL INPUT SIGNAL FREQUENCY (Hz)

2415 F33

–80

–90

–100

–120

–130

–140

INPUT FREQUENCY (Hz)

100

120

140

160

180

200

220

2415 F34

–20

–40

–60

–80

–100

–120

VCC = 5V

REF+ = 5V

REF – = GND

VINCM = 2.5V

VIN(P-P) = 5V

TA = 25°C

MEASURED DATA

CALCULATED DATA

Figure 34. Input Normal Mode Rejection vs Input

Frequency with Input Perturbation of 100% of Full Scale

Figure 30. Rejection vs Frequency at VIN

Figure 31. Rejection vs Frequency at VIN

Figure 32. Rejection vs Frequency at VIN

Figure 33. Normal Mode Rejection

when Using an Internal Oscillator

Normal Mode Rejection, Output Rate and Running

Averages

The LTC2415/LTC2415-1 both contain an identical Sinc4

digital filter (see Figures 30 and 31) which offers excellent

line frequency noise rejection. For the LTC2415, a notch

frequency of either 50Hz or 60Hz (see Figure 32) is user

selectable by tying pin FO high or Low, respectively. On the

other hand, the LTC2415-1 offers simultaneous rejection

of 50Hz and 60Hz by tying FO low. This sets the notch

frequency to approximately 55Hz (see Figure 32).

At a notch frequency of 55Hz, the LTC2415-1 rejects 50Hz

±2% and 60Hz ±2% better than 72dB. In order to achieve

better than 87dB rejection of both 50Hz and 60Hz

±2%, a

running average can be performed. By averaging two

consecutive ADC readings, a Sinc1 notch is combined with

the Sinc4 digital filter yielding the frequency response

shown in Figures 33 and 34. In order to preserve the 2

output rate, adjacent results are averaged with the follow-

ing algorithm:

Result 1 = average (sample 0, sample 1)

Result 2 = average (sample 1, sample 2)

Result 3 = average (sample 2, sample 3)

…

Result N = average (sample n-1, sample n)

LTC2415-1IGN Datasheet(PDF) 32 Page - Linear Technology

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