LM4949 datasheet(36/40 Pages) NSC

36 / 40 page

Application Information (Continued)

Shutdown Function

The LM4949 features five shutdown modes, configured

through the I

2C interface. Bit D0 (PWR_ON) in the Shutdown

Control register shuts down/turns on the entire device. Set

PWR_ON=1to enable the LM4949, set PWR_ON 0 to

disable the device. Bits D0 – D3 in the Output On/Off Control

shutdown/turn on the individual channels. HPR_ON (D3)

controls the right channel headphone output, HPL_ON (D2)

controls the left channel headphone output, LSR_ON (D1)

controls the right channel loudspeaker output, and LRL_ON

(D0) controls the left channel loudspeaker output. The

PWR_ON bit takes precedence over the individual channel

controls.

Audio Amplifier Gain Setting

The each channel of the LM4949 has two separate gain

stages. Each input stage features a 32 step volume control

with a range of -57dB to +18dB (Table 7). Each speaker

output stage has 4 gain settings (Table 8); 0dB, 2dB, 4dB,

and 6dB when either a fully differential signal or two single

ended signals are applied on the _IN+ and _IN- pins; and

6dB, 8dB, 10dB and 12dB in single-ended input mode with

only one signal applied. The headphone gain is not affected

by the input mode. Each headphone output stage has 3 gain

settings (Table 9), 0dB, -6dB, and -12dB. This allows for a

maximum separation of 24dB between the speaker and

headphone outputs when both are active.

Calculate the total gain of a given signal path as follows:

VOL +AOS =ATOTAL

Where A

VOL is the volume control level, AOS is the gain

setting of the output stage, and A

TOTAL is the total gain for the

signal path.

LM4949 Datasheet(PDF) 36 Page - National Semiconductor (TI)