LTC2413IGN datasheet(29/44 Pages) LINER

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LTC2413

sn2413 2413fs

APPLICATIO S I FOR ATIO

Output Data Rate

When using its internal oscillator, the LTC2413 can pro-

duce up to 6.8 readings per second. The actual output data

rate will depend upon the length of the sleep and data

output phases which are controlled by the user and which

can be made insignificantly short. When operated with an

external conversion clock (FO connected to an external

oscillator), the LTC2413 output data rate can be increased

as desired. The duration of the conversion phase is 20510/

fEOSC. If fEOSC = 139800Hz, the converter behaves as if the

internal oscillator is used with simultaneous 50Hz/60Hz

rejection. There is no significant difference in the LTC2413

performance between these two operation modes.

An increase in fEOSC over the nominal 139800Hz will

translate into a proportional increase in the maximum

output data rate. This substantial advantage is neverthe-

less accompanied by three potential effects, which must

be carefully considered.

First, a change in fEOSC will result in a proportional change

in the internal notch position and in a reduction of the

converter differential mode rejection at the power-line

frequency. In many applications, the subsequent perfor-

mance degradation can be substantially reduced by rely-

ing upon the LTC2413’s exceptional common mode rejec-

tion and by carefully eliminating common mode to differ-

ential mode conversion sources in the input circuit. The

user should avoid single-ended input filters and should

maintain a very high degree of matching and symmetry in

the circuits driving the IN+ and IN– pins.

Second, the increase in clock frequency will increase

proportionally the amount of sampling charge transferred

through the input and the reference pins. If large external

input and/or reference capacitors (CIN, CREF) are used, the

previous section provides formulae for evaluating the

effect of the source resistance upon the converter perfor-

mance for any value of fEOSC. If small external input and/

or reference capacitors (CIN, CREF) are used, the effect of

the external source resistance upon the LTC2413 typical

performance can be inferred from Figures 18, 19, 23 and

24 in which the horizontal axis is scaled by 139800/fEOSC.

Figure 27. INL vs Differential Input Voltage (VIN = IN+ – IN–)

and Reference Source Resistance (RSOURCE at REF+ and REF– for

Large CREF Values (CREF ≥ 1µF)

VINDIF/VREFDIF

–0.5 –0.4–0.3–0.2–0.1 0

0.1 0.2 0.3 0.4 0.5

–3

–6

–9

–12

–15

VCC = 5V

REF+ = 5V

REF– = GND

VINCM = 0.5 • (IN

+ + IN–) = 2.5V

FO = GND

CREF = 10µF

TA = 25°C

RSOURCE = 1000Ω

2413 F27

RSOURCE = 100Ω

RSOURCE = 500Ω

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