Datasheet
10 pF
Speaker
Ferrite Bead
LSGND
LM49350
Class D
LS-
LS+
10 pF
Ferrite Bead
LM49350, LM49350RLEVAL
www.ti.com
SNAS359D –SEPTEMBER 2008–REVISED JUNE 2012
Figure 57. EMI/RFI Filter for the Class D Amplifier
Table 19. LEFT HEADPHONE_OUTPUT (0x11h)
Bits Field Description
0 DACR_HPL The right DAC output is added to the left headphone output.
1 DACL_HPL The left DAC output is added to the left headphone output.
2 MICR_HPL The right MIC input is added to the left headphone output. Setting this bit enables MIC BIAS.
3 MICL_HPL The left MIC input is added to the left headphone output. Setting this bit enables MIC BIAS.
4 AUXR_HPL The right AUX input is added to the left headphone output.
5 AUXL_HPL The left AUX input is added to the left headphone output.
Table 20. RIGHT HEADPHONE_OUTPUT (0x12h)
Bits Field Description
0 DACR_HPR The right DAC output is added to the right headphone output.
1 DACL_HPR The left DAC output is added to the right headphone output.
The right MIC input is added to the right headphone output. Setting this bit enables the MIC BIAS
2 MICR_HPR
output.
The left MIC input is added to the right headphone output. Setting this bit enables the MIC BIAS
3 MICL_HPR
output.
4 AUXR_HPR The right AUX input is added to the right headphone output.
5 AUXL_HPR The left AUX input is added to the right headphone output.
HEADPHONE AMPLIFIER FUNCTION
The LM49350 headphone amplifier features TI’s ground referenced architecture that eliminates the large DC-
blocking capacitors required at the outputs of traditional headphone amplifiers. A low-noise inverting charge
pump creates a negative supply (HP_V
SS
) from the positive supply voltage (LS_V
DD
). The headphone amplifiers
operate from these bipolar supplies, with the amplifier outputs biased about GND, instead of a nominal DC
voltage (typically V
DD
/2), like traditional amplifiers. Because there is no DC component to the headphone output
signals, the large DC-blocking capacitors (typically 220μF) are not necessary, conserving board space and
system cost, while improving frequency response.
CHARGE PUMP CAPACITOR SELECTION
Use low ESR ceramic capacitors (less than 100mΩ) for optimum performance.
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