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| SPC560D30X Datasheet, PDF (64/90 Pages) STMicroelectronics – Non-maskable interrupt | |||
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Electrical characteristics
SPC560D30x, SPC56040Dx
EXTERNAL CIRCUIT
Source
RS
VA
Filter
RF
Current Limiter
RL
CF
CP1
INTERNAL CIRCUIT SCHEME
VDD
Channel
Selection
Extended
Switch
Sampling
RSW1
RSW2
RAD
CP3
CP2
CS
RS: Source impedance
RF: Filter resistance
CF: Filter capacitance
RL: Current limiter resistance
RSW1: Channel selection switch impedance (two contributions, RSW1 and RSW2)
RAD: Sampling switch impedance
CP: Pin capacitance (two contributions, CP1, CP2 and CP3)
CS: Sampling capacitance
Figure 13. Input equivalent circuit (extended channels)
A second aspect involving the capacitance network shall be considered. Assuming the three
capacitances CF, CP1 and CP2 are initially charged at the source voltage VA (refer to the
equivalent circuit in Figure 13): A charge sharing phenomenon is installed when the
sampling phase is started (A/D switch close).
VCS
VA
VA2
1
Voltage transient on CS
2
VA1
ïV <ï 0.5 LSBï
ï´1 < (RSW + RAD) CS << ts
ï´2 = RL (CS + CP1 + CP2)
ts
t
64/90
Figure 14. Transient behavior during sampling phase
Doc ID 16315 Rev 7
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