SPC560D30X datasheet(64/90 Pages) STMICROELECTRONICS

64 / 90 page

Electrical characteristics

SPC560D30x, SPC56040Dx

64/90

Doc ID 16315 Rev 7

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).

Figure 14.

Transient behavior during sampling phase

RSW1

CP3

VDD

Sampling

Source

Filter

Current Limiter

EXTERNAL CIRCUIT

INTERNAL CIRCUIT SCHEME

CP1

RAD

Channel

Selection

CP2

Extended

RSW2

Switch

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

VA1

VA2

VCS

Voltage transient on CS

V <0.5 LSB





1 < (RSW + RAD) CS << ts



2 = RL (CS + CP1 + CP2)

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