LM4854 datasheet(18/29 Pages) NSC

18 / 29 page

Typical Performance Characteristics (Continued)

Channel-to-Channel Crosstalk

vs Frequency

Channel-to-Channel Crosstalk

vs Frequency

200382D4

DD = 5V, RL =16

Ω (SE)

A = Left channel driven, right channel measured

B = Right channel driven, left channel measured

200382D5

DD = 5V, RL =32

Ω (SE)

A = Left channel driven, right channel measured

B = Right channel driven, left channel measured

Channel-to-Channel Crosstalk

vs Frequency

Channel-to-Channel Crosstalk

vs Frequency

200382D6

DD = 3V, RL =16

Ω (SE)

A = Left channel driven, right channel measured

B = Right channel driven, left channel measured

200382D7

DD = 3V, RL =32

Ω (SE)

A = Left channel driven, right channel measured

B = Right channel driven, left channel measured

Application Information

ELIMINATING OUTPUT COUPLING CAPACITORS

Typical single-supply audio amplifiers that can switch be-

tween driving bridge-tied-load (BTL) speakers and single-

ended (SE) headphones use a coupling capacitor on each

SE output. This capacitor blocks the half-supply voltage to

which the output amplifiers are typically biased and couples

the audio signal to the headphones. The signal returns to

circuit ground through the headphone jack’s sleeve.

The LM4854 eliminates these coupling capacitors. When the

LM4854 is configured to drive SE loads, AMP2 is internally

configured to apply V

DD/2 to a stereo headphone jack’s

sleeve. This voltage equals the quiescent voltage present on

the Amp1 and Amp3 outputs that drive the headphones.

Headphones driven by the LM4854 operate in a manner very

similar to a BTL load. The same DC voltage is applied to

each input terminal on a headphone speaker. This results in

no net DC current flow through the speaker. AC current flows

through a headphone speaker as an audio signal’s output

amplitude increases on one of the speaker’s terminal.

When operating as a headphone amplifier, the headphone

jack sleeve is not connected to circuit ground, but to V

DD/2.

Using the headphone output jack as a line-level output will

place the LM4854’s one-half supply voltage on a plug’s

sleeve connection. Driving a portable notebook computer or

audio-visual display equipment is possible. This presents no

difficulty when the external equipment uses capacitively

coupled inputs. For the very small minority of equipment that

is DC-coupled, the LM4854 monitors the current supplied by

LM4854 Datasheet(PDF) 18 Page - National Semiconductor (TI)

LM4854 Datasheet(HTML) 18 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 25 26 27 28 29

Datasheet Download

Link URL