CLC446AMC datasheet(4/12 Pages) NSC

4 / 12 page

http://www.national.com

The CLC446 has a current-feedback architecture built in

an advanced complementary bipolar process. The key

features of current-feedback are:

AC bandwidth is independent of voltage gain

Unity-gain stability

Frequency response may be adjusted with Rf

High slew rate

Low variation in performance for a wide range

of gains, signal levels and loads

Fast settling

Current-feedback operation can be explained with a

simple model. The voltage gain for the circuits in Figures

1 and 2 is approximately:

where

Av is the DC voltage gain

Rf is the feedback resistor

Z(j

ω) is the CLC446’s open-loop

transimpedance gain

is the loop-gain

The denominator of the equation above is approximately

low

frequencies.

Near

the

-3dB

corner

frequency, the interaction between Rf and Z(jω)

dominates the circuit performance. Increasing Rf does

the following:

Decreases loop-gain

Decreases bandwidth

Lowers pulse response overshoot

Reduces gain peaking

Affects frequency response phase linearity

CLC446 Operation

The following topics will supply you with:

Design parameters, formulas and techniques

Interfaces

Application circuits

Layout techniques

SPICE model information

DC Gain (non-inverting)

The non-inverting DC voltage gain for the configuration

shown in Figure 1 is

The normalized gain plots in the

Typical Performance

Characteristics

section

show

different

feedback

resistors (Rf) for different gains. These values of Rf are

recommended for obtaining the highest bandwidth with

minimal peaking. The resistor Rt provides DC bias for

the non-inverting input.

For Av < 5, use linear interpolation on the nearest Av val-

ues to calculate the recommended value of Rf. For Av ≥

5, the minimum recommended Rf is 200Ω.

Select Rg to set the DC gain:

DC gain accuracy is usually limited by the tolerance of Rf

and Rg.

Figure 1: Non-Inverting Gain

CLC446

0.1

µF

6.8

µF

Vin

VCC

0.1

µF

6.8

µF

VEE

Typical Performance Characteristics (VCC = ±5V, Av = +2, R

f = 249Ω

Ω,, R

L = 100Ω

Ω; unless specified)

Short Term Settling Time

Time (sec)

0.2

0.1

-0.2

10n

100n

-0.1

VO = 2V step

Long Term Settling Time

Time (s)

0.2

0.1

-0.2

100

-0.1

10m

100m

VO = 2V step

+ ()ω

()

−

CLC446 Design Information

CLC446AMC Datasheet(PDF) 4 Page - National Semiconductor (TI)

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