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32.0 Analog Mixer Control Registers
This register is used to control the LM49360's Analog Mixer:
TABLE 39. CLASS_D_OUTPUT (0x10h)
Bits
Field
Description
0
DACR_LS
The right DAC output is added to the loudspeaker output.
1
DACL_LS
The left DAC output is added to the loudspeaker output.
2
RSVD
Reserved
3
RSVD
Reserved
4
MONO_LS
The MONO input is added to the loudspeaker output.
5
AUX_LS
The AUX input is added to the loudspeaker output.
Class D Loudspeaker Amplifier
The LM49360 features a filterless modulation scheme. The differential outputs of the device switch at 300kHz from V
DD
to GND.
When there is no input signal applied, the two outputs (LS+ and LS-) switch with a 50% duty cycle, with both outputs in phase.
Because the outputs of the LM49360 are differential, the two signals cancel each other. This results in no net voltage across the
speaker, thus there is no load current during an idle state, conserving power.
With an input signal applied, the duty cycle (pulse width) of the LM49360 outputs changes. For increasing output voltages, the duty
cycle of LS+ increases, while the duty cycle of LS- decreases. For decreasing output voltages, the converse occurs, the duty cycle
of LS- increases while the duty cycle of LS+ decreases. The difference between the two pulse widths yields the differential output
voltage.
Spread Spectrum Modulation
The LM49360 features a fitlerless spread spectrum modulation scheme that eliminates the need for output filters, ferrite beads or
chokes. The switching frequency varies by ±30% about a 300kHz center frequency, reducing the wideband spectral content,
improving EMI emissions radiated by the speaker and associated cables and traces. Where a fixed frequency class D exhibits
large amounts of spectral energy at multiples of the switching frequency, the spread spectrum architecture of the LM49360 spreads
that energy over a larger bandwidth. The cycle-to-cycle variation of the switching period does not affect the audio reproduction or
efficiency.
Class D Power Dissipation and Efficiency
In general terms, efficiency is considered to be the ratio of useful work output divided by the total energy required to produce it
with the difference being the power dissipated, typically, in the IC. The key here is “useful” work. For audio systems, the energy
delivered in the audible bands is considered useful including the distortion products of the input signal. Sub-sonic (DC) and super-
sonic components (>22kHz) are not useful. The difference between the power flowing from the power supply and the audio band
power being transduced is dissipated in the LM49360 and in the transducer load. The amount of power dissipation in the LM49360's
class D amplifier is very low. This is because the ON resistance of the switches used to form the output waveforms is typically less
than 0.25
Ω
. This leaves only the transducer load as a potential "sink" for the small excess of input power over audio band output
power. The LM49360 dissipates only a fraction of the excess power requiring no additional PCB area or copper plane to act as a
heat sink.
TABLE 40. 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
RSVD
Reserved
3
RSVD
Reserved
4
MONO_HPL
The MONO input is added to the left headphone output.
5
AUX_HPL
The AUX input is added to the left headphone output.
www.ti.com
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LM49360
Содержание Boomer LM49360
Страница 3: ...5 0 LM49360 Overview 301282h8 FIGURE 1 LM49360 Block Diagram www ti com 2 LM49360...
Страница 4: ...6 0 Typical Application 30128211 FIGURE 2 Sub PMU System Diagram 3 www ti com LM49360...
Страница 5: ...30128216 FIGURE 3 AP PMU System Diagram www ti com 4 LM49360...
Страница 16: ...301282h9 FIGURE 4 PMU State Machine 15 www ti com LM49360...
Страница 68: ...30128213 FIGURE 20 Internal Clock Network 67 www ti com LM49360...
Страница 89: ...301282i1 FIGURE 28 Timing for I2S Master 301282i2 FIGURE 29 Timing for I2S Slave www ti com 88 LM49360...
Страница 128: ...40 0 Schematic Diagram 30128220 FIGURE 36 Demo Board Schematic 127 www ti com LM49360...
Страница 129: ...30128245 FIGURE 37 Demo Board Schematic www ti com 128 LM49360...
Страница 130: ...41 0 Demonstration Board Layout 30128243 FIGURE 38 Top Silkscreen 30128244 FIGURE 39 Top Layer 129 www ti com LM49360...
Страница 131: ...30128238 FIGURE 40 Inner Layer 2 30128239 FIGURE 41 Inner Layer 3 www ti com 130 LM49360...
Страница 132: ...30128240 FIGURE 42 Inner Layer 4 30128241 FIGURE 43 Inner Layer 5 131 www ti com LM49360...
Страница 133: ...30128231 FIGURE 44 Bottom Layer 30128242 FIGURE 45 Bottom Silkscreen www ti com 132 LM49360...
Страница 136: ...Notes 135 www ti com LM49360...