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LTC2439-1 Datasheet(PDF) 21 Page - Linear Technology |
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LTC2439-1 Datasheet(HTML) 21 Page - Linear Technology |
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21 / 28 page  LTC2439-1 21 24391f Figure 12), a first order passive network with a time constant τ = (RS + RSW) • CEQ. The converter is able to sample the input signal with better than 1LSB accuracy if the sampling period is at least 11 times greater than the input circuit time constant τ. The sampling process on the four input analog pins is quasi-independent so each time constant should be considered by itself and, under worst- case circumstances, the errors may add. When using the internal oscillator (FO = LOW), the LTC2439-1’s front-end switched-capacitor network is clocked at 69900Hz corresponding to a 14.3 µs sampling period. Thus, for settling errors of less than 1LSB, the driving source impedance should be chosen such that τ ≤ 14.3µs/11 = 1.3µs. When an external oscillator of APPLICATIO S I FOR ATIO frequency fEOSC is used, the sampling period is 2/fEOSC and, for a settling error of less than 1LSB, τ ≤ 0.18/fEOSC. Input Current If complete settling occurs on the input, conversion re- sults will be unaffected by the dynamic input current. An incomplete settling of the input signal sampling process may result in gain and offset errors, but it will not degrade the INL performance of the converter. Figure 12 shows the mathematical expressions for the average bias currents flowing through the IN+ and IN– pins as a result of the sampling charge transfers when integrated over a sub- stantial time period (longer than 64 internal clock cycles). VREF+ VIN+ VCC RSW (TYP) 20k ILEAK ILEAK VCC ILEAK ILEAK VCC RSW (TYP) 20k CEQ 18pF (TYP) RSW (TYP) 20k ILEAK IIN+ VIN– IIN– IREF+ IREF– 24391 F11 ILEAK VCC ILEAK ILEAK SWITCHING FREQUENCY fSW = 69900Hz INTERNAL OSCILLATOR (FO = LOW) fSW = 0.5 • fEOSC EXTERNAL OSCILLATOR VREF– RSW (TYP) 20k Figure 12. LTC2439-1 Equivalent Analog Input Circuit IIN VV V R IIN VV V R I REF VV V R V VR I REF VV V R V VR where AVG IN INCM REFCM EQ AVG IN INCM REFCM EQ AVG REF INCM REFCM EQ IN REF EQ AVG REF INCM REFCM EQ IN REF EQ + − + − () = +− • () = −+ − • () = •− + • − • () = −• − + • + • 05 05 15 05 15 05 2 2 . . . . . . :: ./ ./ V REF REF V REF REF VIN IN V IN IN R M INTERNAL OSCILLATOR Hz Hz Notch F LOW R f EXTERNAL OSCILLATOR REF REFCM IN INCM EQ O EQ EOSC =− = + =− = − == () =• () +− +− +− +− 2 2 397 50 60 0 555 1012 Ω |
Similar Part No. - LTC2439-1 |
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Similar Description - LTC2439-1 |
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