LM49150, LM49150TLEVAL

www.ti.com

SNAS439C – AUGUST 2008 – REVISED MAY 2013

INPUT MIXER/MULTIPLEXER

The LM49150 includes a comprehensive mixer multiplexer controlled through the I2C interface. The

mixer/multiplexer allows any input combination to appear on any output of LM49150. Multiple input paths can be

selected simultaneously. Under these conditions, the selected inputs are mixed together and output on the

selected channel. Table 5 shows how the input signals are mixed together for each possible input selection.

CLASS D AMPLIFIER

The LM49150 features a high-efficiency, filterless, class D amplifier, which features a filterless modulation

scheme. When there is no input signal applied, the output switches between VDD and GND at a 50% duty cycle.

Since the outputs of the LM49150 class D amplifier are differential and in phase, the result is zero net voltage

across the speaker and no load current during the ideal state, thus conserving power. The switching frequency of

each output is 300kHz.

When an input signal is applied, the duty cycle (pulse width) changes. For increasing output voltages, the duty

cycle of one output increases while the duty cycle of the output decreases. For decreasing output voltages, the

converse occurs. The difference between the two pulse widths yields the differential output voltage across the

load.

SPREAD SPECTRUM

The LM49150 features a filterless spread spectrum modulation scheme. The switching frequency varies by +/-

30% about a 300kHz center frequency, reducing the wideband spectral content, reducing EMI emissions radiated

by the speaker and associated cables and traces. When a fixed frequency class D exhibits large amounts of

spectral energy at multiples of switching frequency, the spread spectrum architecture of the LM49150 spreads

that energy over a larger bandwidth. The cycle-to-cycle variation of the switching period does not affect the audio

reproduction, efficiency, or PSRR. To enable spread spectrum, set the spread spectrum bit, B5 = 1 of the

SHUTDOWN CONTROL register (see Table 3).

ENHANCED EMMISIONS SUPPRESSION (E

2S)

The LM49150 features TI’s patented E2S system that reduces EMI, while maintaining high quality audio

reproduction and efficiency. The LM49150 features Edge Rate Control (ERC) that greatly reduces the high

frequency components of the output square waves by controlling the output rise and fall times, slowing the

transitions to reduce RF emissions, while optimizing THD+N and efficiency performance.

LDO GENERAL INFORMATION

The LM49150 has different supplies for each portion of the device, allowing for the optimum combination of

headroom, power dissipation and noise immunity. The speaker amplifiers are powered from LSVDD. The ground

reference headphone amplifiers are powered from the internal LDO. The separate power supplies allow the

loudspeaker amplifier to operate from a higher voltage for maximum headroom, while the headphone amplifiers

operate from a lower voltage, improving power dissipation.

GROUND REFERENCED HEADPHONE AMPLIFIER

The LM49150 features a low noise inverting charge pump that generates an internal negative supply voltage.

This allows the headphone outputs to be biased about GND instead of a nominal DC voltage, like traditional

headphone amplifiers. Because there is no DC component, the large DC blocking capacitors (typically 220

μF)

are not necessary. The coupling capacitors are replaced by two small ceramic charge pump capacitors, saving

board space and cost. Eliminating the output coupling capacitors also improves low frequency response. In

traditional headphone amplifiers, the headphone impedance and the output capacitor from a high-pass filter that

not only blocks the DC component of the output, but also attenuates low frequencies, impacting the bass

response. Because the LM49150 does not require the output coupling capacitors, the low frequency response of

the device is not degraded by external components. In addition to eliminating the output coupling capacitors, the

ground referenced output nearly doubles the available dynamic range of the LM49250 headphone amplifiers

when compared to a traditional headphone amplifier operating from the same supply voltage.

CHARGE PUMP CAPACITOR SELECTION

Use low ESR ceramic capacitors (less than 100m

Ω) for optimum performance.

Copyright © 2008–2013, Texas Instruments Incorporated

Submit Documentation Feedback

21

Product Folder Links: LM49150 LM49150TLEVAL