LM4781, LM4781TABD

SNAS208A – AUGUST 2003 – REVISED APRIL 2013

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External Components Description

Figure 1, Figure 3, Figure 4, Figure 5, and Figure 6

Components

Functional Description

1

Prevents current from entering the amplifier's non-inverting input. This current may pass through to the load during

system power down, because of the amplifier's low input impedance when the undervoltage circuitry is off. This

2

3

4

Feedback resistance. Works with Cf and Rf creating a lowpass filter that lowers AC gain at high frequencies. The -

(1)

Figure 6.

5

(1)

6

Compensation capacitor. Reduces the gain at higher frequencies to avoid quasi-saturation oscillations of the output

(1)

transistor. Also suppresses external electromagnetic switching noise created from fluorescent lamps.

7

(1)

8

Provides power supply filtering and bypassing. Refer to the SUPPLY BYPASSING application section for proper

placement and selection of bypass capacitors.

9

Acts as a volume control by setting the input voltage level.

(1)

10

(1)

when the inputs are floating. Recommended values are 10k

Ω to 47kΩ. Refer to Figure 6.

11

Input capacitor. Prevents the input signal's DC offsets from being passed onto the amplifier's inputs.

(1)

12

(1)

13

(1)

14

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

the series resonant circuit. Also provides a low impedance at low frequencies to short out R and pass audio signals

15

to the load. Refer to Figure 6.

16

Provides DC voltage biasing for the transistor Q1 in single supply operation.

17

Provides bias filtering for single supply operation.

18

Limits the voltage difference between the amplifier's inputs for single supply operation. Refer to the CLICKS AND

(1)

19

Provides input bias current for single supply operation. Refer to the CLICKS AND POPS application section for a

20

Establishes a fixed DC current for the transistor Q1 in single supply operation. This resistor stabilizes the half-

21

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

curves in the Typical Performance Characteristics section.

22

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

23

Mute switch. When open or switched to GND, the amplifier will be in mute mode.

24

Reduces current flow between outputs that are caused by Gain or DC offset differences between the amplifiers.

(1)

Optional components dependent upon specific design requirements.

8

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