MPC5607B datasheet(75/112 Pages) FREESCALE

75 / 112 page

Electrical characteristics

MPC5607B Microcontroller Data Sheet, Rev. 8

Freescale Semiconductor

In fact a current sink contributor is represented by the charge sharing effects with the sampling capacitance: being CS and Cp2

substantially two switched capacitances, with a frequency equal to the conversion rate of the ADC, it can be seen as a resistive

path to ground. For instance, assuming a conversion rate of 1 MHz, with CS+Cp2 equal to 3 pF, a resistance of 330 k is

obtained (REQ = 1 / (fc ×(CS+Cp2)), where fc represents the conversion rate at the considered channel). To minimize the error

induced by the voltage partitioning between this resistance (sampled voltage on CS+Cp2) and the sum of RS + RF, the external

circuit must be designed to respect the Equation 4:

Eqn. 4

Equation 4 generates a constraint for external network design, in particular on a resistive path.

Figure 17. Input equivalent circuit (precise channels)

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

---LSB



RSW1

CP2

VDD

Sampling

Source

Filter

Current Limiter

EXTERNAL CIRCUIT

INTERNAL CIRCUIT SCHEME

Source Impedance

Filter Resistance

Filter Capacitance

Current Limiter Resistance

RSW1 Channel Selection Switch Impedance

RAD Sampling Switch Impedance

Pin Capacitance (two contributions, CP1 and CP2)

Sampling Capacitance

CP1

RAD

Channel

Selection

MPC5607B Datasheet(PDF) 75 Page - Freescale Semiconductor, Inc