LTC2410 24-Bit No Latency âÎ£TM ADC with Differential Input and ...

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LTC2410APPLICATIO S I FORATIOU W U UREF + and REF – pins and external capacitance C REF connectedto these pins are shown in Figures 22, 23, 24and␣ 25.In addition to this gain error, the converter INL performanceis degraded by the reference source impedance.When F O = LOW (internal oscillator and 60Hz notch), every100Ω of source resistance driving REF + or REF – translatesinto about 1.34ppm additional INL error. When F O = HIGH(internal oscillator and 50Hz notch), every 100Ω of sourceresistance driving REF + or REF – translates into about1.1ppm additional INL error. When F O is driven by anexternal oscillator with a frequency f EOSC , every 100Ω ofsource resistance driving REF + or REF – translates intoabout 8.73 • 10 –6 • f EOSC ppm additional INL error.Figure␣ 26 shows the typical INL error due to the sourceresistance driving the REF + or REF – pins when large C REFvalues are used. The effect of the source resistance on thetwo reference pins is additive with respect to this INL error.In general, matching of source impedance for the REF +and REF – pins does not help the gain or the INL error. Theuser is thus advised to minimize the combined sourceimpedance driving the REF + and REF – pins rather than totry to match it.+FS ERROR (ppm OF V REF )0–10–20–30–40–50V CC = 5VREF + = 5VREF – = GNDIN + = 5VIN – = 2.5VF O = GNDT A = 25°CC REF = 0.01µFC REF = 0.001µFC REF = 100pFC REF = 0pF1 10 100 1k 10k 100kR SOURCE (Ω)2410 F22–FS ERROR (ppm OF V REF )50403020100C REF = 0.01µFC REF = 0.001µFC REF = 100pFV CC = 5VREF + = 5VREF – = GNDIN + = GNDIN – = 2.5VF O = GNDT A = 25°CC REF = 0pF1 10 100 1k 10k 100kR SOURCE (Ω)2410 F23Figure 22. +FS Error vs R SOURCE at REF + or REF – (Small C IN ) Figure 23. –FS Error vs R SOURCE at REF + or REF – (Small C IN )+FS ERROR (ppm OF V REF )0–90–180–270–360–450V CC = 5VREF + = 5VREF – = GNDIN + = 3.75VIN – = 1.25VF O = GNDT A = 25°CC REF = 0.01µFC REF = 0.1µFC REF = 1µF, 10µF0 100 200 300 400 500 600 700 800 900 1000R SOURCE (Ω)2410 F24–FS ERROR (ppm OF VREF)450360270180900V CC = 5VREF + = 5VREF – = GNDIN + = 1.25VIN – = 3.75VF O = GNDT A = 25°CC REF = 1µF, 10µFC REF = 0.1µFC REF = 0.01µF0 100 200 300 400 500 600 700 800 900 1000R SOURCE (Ω)2410 F25Figure 24. +FS Error vs R SOURCE at REF + and REF – (Large C REF ) Figure 25. –FS Error vs R SOURCE at REF + and REF – (Large C REF )28
LTC2410APPLICATIO S I FORINL (ppm OF V REF )15129630–3–6–9–12ATIOU W U UR SOURCE = 100ΩR SOURCE = 1000ΩR SOURCE = 500Ω–15–0.5–0.4–0.3–0.2–0.1 0 0.1 0.2 0.3 0.4 0.5V INDIF /V REFDIFV CC = 5VREF+ = 5VREF– = GNDV INCM = 0.5 • (IN + + IN – ) = 2.5VF O = GNDC REF = 10µFT A = 25°C2410 F26Figure 26. INL vs Differential Input Voltage (V IN = IN + – IN – )and Reference Source Resistance (R SOURCE at REF + and REF – forLarge C REF Values (C REF ≥ 1µF)The magnitude of the dynamic reference current dependsupon the size of the very stable internal sampling capacitorsand upon the accuracy of the converter samplingclock. The accuracy of the internal clock over the entiretemperature and power supply range is typical better than0.5%. Such a specification can also be easily achieved byan external clock. When relatively stable resistors(50ppm/°C) are used for the external source impedanceseen by REF + and REF – , the expected drift of the dynamiccurrent gain error will be insignificant (about 1% of itsvalue over the entire temperature and voltage range). Evenfor the most stringent applications a one-time calibrationoperation may be sufficient.In addition to the reference sampling charge, the referencepins ESD protection diodes have a temperature dependentleakage current. This leakage current, nominally 1nA(±10nA max), results in a small gain error. A 100Ω sourceresistance will create a 0.05µV typical and 0.5µV maximumfull-scale error.Output Data RateWhen using its internal oscillator, the LTC2410 can produceup to 7.5 readings per second with a notch frequencyof 60Hz (F O = LOW) and 6.25 readings per second with anotch frequency of 50Hz (F O = HIGH). The actual outputdata rate will depend upon the length of the sleep and dataoutput phases which are controlled by the user and whichcan be made insignificantly short. When operated with anexternal conversion clock (F O connected to an externaloscillator), the LTC2410 output data rate can be increasedas desired. The duration of the conversion phase is 20510/f EOSC . If f EOSC = 153600Hz, the converter behaves as if theinternal oscillator is used and the notch is set at 60Hz.There is no significant difference in the LTC2410 performancebetween these two operation modes.An increase in f EOSC over the nominal 153600Hz willtranslate into a proportional increase in the maximumoutput data rate. This substantial advantage is neverthelessaccompanied by three potential effects, which mustbe carefully considered.First, a change in f EOSC will result in a proportional changein the internal notch position and in a reduction of theconverter differential mode rejection at the power linefrequency. In many applications, the subsequent performancedegradation can be substantially reduced by relyingupon the LTC2410’s exceptional common mode rejectionand by carefully eliminating common mode to differentialmode conversion sources in the input circuit. Theuser should avoid single-ended input filters and shouldmaintain a very high degree of matching and symmetry inthe circuits driving the IN + and IN – pins.Second, the increase in clock frequency will increaseproportionally the amount of sampling charge transferredthrough the input and the reference pins. If large externalinput and/or reference capacitors (C IN , C REF ) are used, theprevious section provides formulae for evaluating theeffect of the source resistance upon the converter performancefor any value of f EOSC . If small external input and/or reference capacitors (C IN , C REF ) are used, the effect ofthe external source resistance upon the LTC2410 typicalperformance can be inferred from Figures 17, 18, 22 and23 in which the horizontal axis is scaled by 153600/f EOSC .Third, an increase in the frequency of the external oscillatorabove 460800Hz (a more than 3× increase in the outputdata rate) will start to decrease the effectiveness of theinternal autocalibration circuits. This will result in a progressivedegradation in the converter accuracy and linear-29
Page 1 and 2: FEATURES■■■■■■■■■
Page 3 and 4: CO VERTER CHARACTERISTICSUThe ● d
Page 5: TII G CHARACTERISTICSU WLTC2410The
Page 9 and 10: LTC2410TYPICAL PERFOR A CE CHARACTE
Page 11 and 12: LTC2410WFU CTIO AL BLOCK DIAGRAV CC
Page 13 and 14: LTC2410APPLICATIO S I FORATIOU W U
Page 17: LTC2410APPLICATIO S I FORATIOU W U
Page 26 and 27: LTC2410APPLICATIO S I FOR26ATIOU W
Page 44 and 45: LTC2410TYPICAL APPLICATIO SU*******
Page 46 and 47: LTC2410TYPICAL APPLICATIO SV CCBANA
Page 48: LTC2410U WPCB LAYOUT A D FILBottom

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LTC2410 24-Bit No Latency âÎ£TM ADC with Differential Input and ...