LM4780 datasheet(8/24 Pages) NSC

8 / 24 page

External Components Description

(Figures 1-5)

Components

Functional Description

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 phenomenon occurs when the V

+ and V- supply voltages are below 1.5V.

Inverting input resistance. Along with R

f, sets AC gain.

Feedback resistance. Along with R

i, sets AC gain.

(Note 17)

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

frequencies. The -3dB point of the pole occurs when: (R

f -Ri)/2=Rf // [1/(2

πf

cCf)+Rf2] for the

Non-Inverting configuration shown in Figure 5.

(Note 17)

Compensation capacitor. Works with R

f and Rf2 to reduce AC gain at higher frequencies.

(Note 17)

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

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

(Note 17)

Feedback capacitor which ensures unity gain at DC. Along with R

i also creates a highpass filter at fc =

1/(2

πR

iCi).

Provides power supply filtering and bypassing. Refer to the Supply Bypassing application section for proper

placement and selection of bypass capacitors.

(Note 17)

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

(Note 17)

Sets the amplifier’s input terminals DC bias point when C

IN is present in the circuit. Also works with CIN to

create a highpass filter at f

C = 1/(2

πR

INCIN). If the value of RIN is too large, oscillations may be observed on

the outputs when the inputs are floating. Recommended values are 10k

Ω to 47kΩ. Refer to Figure 5.

(Note 17)

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

(Note 17)

Works with C

SN to stabilize the output stage by creating a pole that reduces high frequency instabilities.

(Note 17)

Works with R

SN to stabilize the output stage by creating a pole that reduces high frequency instabilities. The

pole is set at f

C = 1/(2

πR

SNCSN). Refer to Figure 5.

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. Also provides a low impedance at low frequencies to short out R and

pass audio signals to the load. Refer to Figure 5.

R (Note 17)

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

Provides bias filtering for single supply operation.

INP

(Note 17)

Limits the voltage difference between the amplifier’s inputs for single supply operation. Refer to the Clicks

and Pops application section for a more detailed explanation of the function of R

INP.

Provides input bias current for single supply operation. Refer to the Clicks and Pops application section for

a more detailed explanation of the function of R

BI.

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

half-supply point along with C

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

→ R

M is calculated using: RM

≤ (|V

EE| − 2.6V)/l where l

≥ 0.5mA. Refer to the Mute Attenuation vs Mute

Current curves in the Typical Performance Characteristics section.

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

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

OUT

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

amplifiers.

Note 17: Optional components dependent upon specific design requirements.

LM4780 Datasheet(PDF) 8 Page - National Semiconductor (TI)

LM4780 Datasheet(HTML) 8 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Datasheet Download

Link URL