MCP6231 datasheet(14/40 Pages) MICROCHIP

14 / 40 page

MCP6231/1R/1U/2/4

DS21881E-page 14

To minimize output offset voltage and increase circuit

accuracy, the resistor values need to meet the

conditions:

EQUATION 4-3:

4.7.2

COMPENSATING FOR THE

PARASITIC CAPACITANCE

In analog circuit design, the PCB parasitic capacitance

can compromise the circuit behavior; Figure 4-9 shows

a typical scenario. If the input of an amplifier sees

parasitic capacitance of several picofarad (CPARA,

which includes the common mode capacitance of 6 pF,

typical), and large RF and RG, the frequency response

of the circuit will include a zero. This parasitic zero

introduces

gain-peaking

and

can

cause

circuit

instability.

FIGURE 4-9:

Effect of Parasitic

Capacitance at the Input.

One solution is to use smaller resistor values to push

the zero to a higher frequency. Another solution is to

compensate by introducing a pole at the point at which

the zero occurs. This can be done by adding CF in

parallel with the feedback resistor (RF). CF needs to be

selected so that the ratio CPARA:CF is equal to the ratio

of RF:RG.

VIN+

VIN –

VOUT

VDC

–

VAC

CPARA

PARA

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MCP623X

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