STR720 datasheet(390/401 Pages) STMICROELECTRONICS

390 / 401 page

STR720 - ELECTRICAL CHARACTERISTICS

390/401

Here you can find an equivalent circuit of ADC input pin modeling the behaviour during the

sampling phase.

Just after the sampling phase is over, the charge on pin capacitors has to be restored by the

signal voltage source. This can be modeled as a current requested by ADC input pin

depending on the frequency with which the pin is sampled by ADC (which is not the signal

sampling frequency due to the oversampling architecture of Sigma-Delta converters).

Equivalent input circuit modeling this aspect can be depicted as illustrated in Figure 80.

Figure 79. ADC input pin equivalent circuit during sampling

Figure 80. ADC input pin equivalent circuit

RSW

CP2

VDD

Sampling

Source

Filter

Current Limiter

EXTERNAL CIRCUIT

INTERNAL CIRCUIT SCHEME

Source Impedance

Filter Resistance

Filter Capacitance

Current Limiter Resistance

RSW Channel Selection Switch Impedance

RAD

Sampling Switch Impedance

Pin Capacitance (two contributions, CP1 and CP2)

Sampling Capacitance

CP1

RAD

Channel

Selection

RIN

VCM

Source

Filter

Current Limiter

EXTERNAL CIRCUIT

INTERNAL CIRCUIT SCHEME

RIN

Equivalent input resistance

VCM

Common mode voltage

STR720 Datasheet(PDF) 390 Page - STMicroelectronics

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