MC33178 데이터 시트보기 (PDF) - Motorola => Freescale

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MC33178

High Output Current Low Power, Low Noise Operational Amplifiers

Motorola => Freescale 

MC33178 MC33179

If a high source of resistance is used (R1 > 1.0 kΩ), a

compensation capacitor equal to or greater than the input

capacitance of the op amp (10 pF) placed across the

feedback resistor (see Figure 34) can be used to neutralize

that pole and prevent outer loop oscillation. Since the closed

loop transient response will be a function of that capacitance,

it is important to choose the optimum value for that capacitor.

This can be determined by the following Equation:

 CC = (1 +[R1/R2])2 CL (ZO/R2)

(1)

where: ZO is the output impedance of the op amp.

For moderately high capacitive loads (500 pF < CL

< 1500 pF) the addition of a compensation resistor on the

order of 20 Ω between the output and the feedback loop will

help to decrease miller loop oscillation (see Figure 35). For

high capacitive loads (CL > 1500 pF), a combined

compensation scheme should be used (see Figure 36). Both

the compensation resistor and the compensation capacitor

affect the transient response and can be calculated for

optimum performance. The value of CC can be calculated

using Equation (1). The Equation to calculate RC is as

follows:

 RC = ZO R1/R2

(2)

Figure 34. Compensation for

High Source Impedance

R2

CC

–

+

R1

ZL

Figure 35. Compensation Circuit for

Moderate Capacitive Loads

R2

–

RC

R1

+

CL

Figure 36. Compensation Circuit for

High Capacitive Loads

R2

CC

–

R1

+

RC

CL

10

MOTOROLA ANALOG IC DEVICE DATA

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