External Components Description

(

Figure 1 and Figure 2)

Components

Functional Description

1.

R

IN

Acts as a volume control by setting the voltage level allowed to the amplifier’s input terminals.

2.

R

A

Provides DC voltage biasing for the single supply operation and bias current for the positive input terminal.

3.

C

A

Provides bias filtering.

4.

C

Provides AC coupling at the input and output of the amplifier for single supply operation.

5.

R

B

Prevents currents from entering the amplifier’s non-inverting input which may be passed through to the load

upon power-down of the system due to the low input impedance of the circuitry when the under-voltage

circuitry is off. This phenomenon occurs when the supply voltages are below 1.5V.

6.

C

C

(Note 17)

Reduces the gain (bandwidth of the amplifier) at high frequencies to avoid quasi-saturation oscillations of

the output transistor. The capacitor also suppresses external electromagnetic switching noise created from

fluorescent lamps.

7.

Ri

Inverting input resistance to provide AC Gain in conjunction with R

8.

Ci

(Note 17)

Feedback capacitor. Ensures unity gain at DC. Also a low frequency pole (highpass roll-off) at:

f

9.

R

f1

Feedback resistance to provide AC Gain in conjunction with Ri.

10.

R

f2

(Note 17)

At higher frequencies feedback resistance works with C

and Ri. A high frequency pole (lowpass roll-off) exists at:

f

11.

C

f

(Note 17)

Compensation capacitor that works with R

12.

R

M

Mute resistance set up to allow 0.5 mA to be drawn from pin 8 to turn the muting function off.

→R

Mute Current curves in the Typical Performance Characteristics section.

13.

C

M

Mute capacitance set up to create a large time constant for turn-on and turn-off muting.

14.

R

SN

(Note 17)

Works with C

15.

C

SN

(Note 17)

Works with R

f

16.

L

(Note 17)

Provides high impedance at high frequencies so that R may decouple a highly capacitive load and reduce

the Q of the series resonant circuit due to capacitive load. Also provides a low impedance at low

frequencies to short out R and pass audio signals to the load.

17.

R

(Note 17)

18.

C

S

Provides power supply filtering and bypassing.

19.

S1

Mute switch that mutes the music going into the amplifier when opened.

Note 17: Optional components dependent upon specific design requirements. Refer to the Application Information section for more information.

OPTIONAL EXTERNAL COMPONENT INTERACTION

Although the optional external components have specific desired functions that are designed to reduce the bandwidth and elimi-

nate unwanted high frequency oscillations they may cause certain undesirable effects when they interact. Interaction may occur

for components whose reactances are in close proximity to one another. One example would be the coupling capacitor, C

the compensation capacitor, C

from the input to the output. Please take careful note of basic amplifier component functionality when designing in these compo-

nents.

The optional external components shown in

Figure 2 and described above are applicable in both single and split voltage supply

configurations.

www.national.com

7