SPC560P34L1 datasheet(70/103 Pages) STMICROELECTRONICS

70 / 103 page

Electrical characteristics

SPC560P34L1, SPC560P34L3, SPC560P40L1, SPC560P40L3

70/103

Doc ID 16100 Rev 7

Figure 16.

Input equivalent circuit

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 reported in Figure 16): A charge sharing phenomenon is installed when

the sampling phase is started (A/D switch closed).

Figure 17.

Transient behavior during sampling phase

RSW

CP2

VDD

Sampling

Source

Filter

Current Limiter

EXTERNAL CIRCUIT

INTERNAL CIRCUIT SCHEME

CP1

RAD

Channel

Selection

RS: Source impedance

RF: Filter resistance

CF: Filter capacitance

RL: Current limiter resistance

RSW: Channel selection switch impedance

RAD: Sampling switch impedance

CP: Pin capacitance (two contributions, CP1 and CP2)

CS: Sampling capacitance

VA1

VA2

VCS

Voltage Transient on CS

ΔV < 0.5 LSB

τ1 < (RSW + RAD) CS << TS

τ2 = RL (CS + CP1 + CP2)

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