National Semiconductor LM49250, Руководство пользователя, Страница: 5 / 10

Spread Spectrum
The LM49250 features a filterless spread spectrum modula-
tion scheme. The switching frequency varies which reduces
the wideband spectral content. This improves EMI emissions
radiated by the speaker and associated cables and traces.
The spread spectrum function can be turned on and off
through the “SS” section of the interface software.
Input Audio Signal Selection
The LM49250 has a single mono differential input and left and
right stereo inputs that can be configured for both single end-
ed and differential audio signals. The stereo input configura-
tions can be set in the “STEREO INPUT CONFIGURATION”
portion of the software interface. Select “FULLY DIFFEREN-
TIAL INPUT MODE” to configure the left and right inputs for
differential operation. Select “L2 and R2 SINGLE-ENDED
STEREO PAIR” to configure the device to accept single end-
ed audio inputs connected to L2 and R2. Select “L1 and R1
SINGLE-ENDED STEREO PAIR” to configure the device to
accept single ended audio inputs connected to L1 and R2.
Select “(L1 mix L2) and (R1 mix R2) SINGLE ENDED
STEREO PAIR” to configure the device to accept two single
ended stereo sources, connected to both input pairs.
Volume Control and Gain Setting
Each channel of the LM49250 has two separate gain stages.
Each input stage (mono, left and right) features a 32 step vol-
ume control that can be configured through the “INPUT VOL-
UME CONTROL” section of the interface software. The
output gain settings can be set under the “Output Gain Set-
tings” tab in the interface software. The loudspeaker output
gain for the left and right channels are set independently,
while the headphone gain is the same for both left and right
channels. The earpiece output stage has two gain settings,
0dB and 6dB. Each loud speaker output stage has two gain
settings, 6dB and 12dB. The headphone output stage has 8
gain settings, 0dB, -1.2dB, -2.5dB, -4dB, -6dB, -8.5dB, -12dB
and -18dB. In single-ended input mode with only one stereo
signal applied, the loudspeaker and headphone output stage
gain settings are increased by 6dB. The total gain for a given
signal path can be calculated by adding the input volume
control gain to the output gain setting.
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