LM48512TLSLASHNOPB datasheet(10/22 Pages) TI

10 / 22 page

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LM48512

SNAS497A – OCTOBER 2010 – REVISED APRIL 2012

www.ti.com

Boost Output Voltage

Load Current

VDD = 3.6V

VDD = 5.0V

Application Information

GENERAL AMPLIFIER FUNCTION

The LM48512 mono Class D audio power amplifier features a filterless modulation scheme that reduces external

component count, conserving board space and reducing system cost. The outputs of the device transition from

VDD to GND with a 300kHz switching frequency. With no signal applied, the outputs (VOUTA and VOUTB) switch

with a 50% duty cycle, in phase, causing the two outputs to cancel. This cancellation results in no net voltage

across the speaker, thus there is no current to the load in the idle state.

With the input signal applied, the duty cycle (pulse width) of the LM48512 outputs changes. For increasing output

voltage, the duty cycle of VOUTA increases, while the duty cycle of VOUTB decreases. For decreasing output

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

ENHANCED EMISSIONS SUPPRESSION SYSTEM (E2S)

The LM48512 features National’s patent-pending E2S system that reduces EMI, while maintaining high quality

audio reproduction and efficiency. The E2S system features advanced edge rate control (ERC), greatly reducing

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 maximizing THD+N and efficiency performance. The overall result

of the E2S system is a filterless Class D amplifier that passes FCC Class B radiated emissions standards with

20in of twisted pair cable, with excellent 0.03% THD+N and high 82% efficiency.

DIFFERENTIAL AMPLIFIER EXPLANATION

As logic supplies continue to shrink, system designers are increasingly turning to differential analog signal

handling to preserve signal to noise ratios with restricted supply level. The LM48512 features a fully differential

speaker amplifier. A differential amplifier amplifies the difference between the two input signals. Traditional audio

power amplifiers have typically offered only single-ended inputs resulting in a 6dB reduction of SNR relative to

differential inputs. The LM48512 also offers the possibility of DC input coupling which eliminates the input

coupling capacitors. A major benefit of the fully differential amplifier is the improved common mode rejection ratio

(CMRR) over single ended input amplifiers. The increased CMRR of the differential amplifier reduces sensitivity

to ground offset related noise injection, especially important in noisy systems.

When evaluating the LM48512, use BAL-GND inputs and provide clean grounding to ensure proper operation.

SYNCHRONOUS RECTIFIER

The LM48512 uses an internal synchronous series switch in place of an external Schottcky diode, which reduces

the number of external components required for its application. Efficiency is also increased since the power

dissipation of the switch is less than the power dissipation of a diode.

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