Product category: Analogue and Mixed Signal ICs
News Release from: National Semiconductor | Subject: LM4675
Edited by the Electronicstalk Editorial Team on 25 October 2006
Audio amp keeps quiet about handheld
interference
Audio amplifier reduces EMI more than 11dB below the FCC limit to lower system noise in portable devices.
A new mono, 2.65W, Class D Boomer audio amplifier from National Semiconductor Corp reduces electromagnetic interference (EMI) more than 11dB below the US Federal Communications Commission (FCC) limit to lower system noise in portable devices including cellphones, smart phones, music players, notebook computers, DVD players, gaming devices and other portable electronics The LM4675 is a single-supply filter-less high-power-output Class D mono audio amplifier in space-saving LLP or 0.5mm-pitch micro SMD packages
This article was originally published on Electronicstalk on 5 Jan 2001 at 8.00am (UK)
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This new class of power amplifier employs a unique spread spectrum technology and a low-noise filter-less pulsewidth modulation (PWM) architecture that significantly lowers electromagnetic interference (EMI) and eliminates output filters.
This combination reduces external component count, saves board space, lowers system cost and simplifies circuit design.
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New from National Semiconductor, the LM4811 Boomer audio amplifier is a 105mW stereo headphone amplifier for use in 3 and 5V systems requiring a headphone output and volume control.
With a 3.6V supply driving an 8ohm speaker, the amplifiers' efficiency for a 100mW power level will be greater than 80%, reaching 89% at 400mW output power.
The company plans to leverage this ultra-low EMI technology for future products, including a stereo version of the LM4675.
National's LM4675 consumes 1.6mA of power at a 2.7V supply, enabling longer talk times in mobile phones and more listening or playing time for portable devices.
The device operates on a wide power supply voltage range of 2.4 to 5.5V.
National designed the amplifier with added features such as differential inputs for reduce noise.
The amp also includes the industry's lowest-current shutdown mode, output short circuit and thermal overload protection, as well as internal, advanced pop-and-click circuitry that eliminates output transients which would otherwise occur during power or shutdown cycles.
The gain of the LM4675 is externally configurable, allowing users to connect different multiple inputs while optimising the gain for each source or system.
Operating on a single 5V supply, the LM4675 drives a 4ohm speaker load at 2.2W continuous output with less than 1% total harmonic distortion plus noise (THD+N).
In addition to its industry-leading low quiescent current, the LM4675 offers a power supply rejection ratio (PSRR) of 82dB at 217Hz, a common-mode rejection ratio (CMRR) of 80dB and a signal-to-noise ratio (SNR) of 82dB.
It also has a typical fast turn-on time of 17us.
Available now, the LM4675 is priced at US $0.98 in an 8-pin LLP package and $0.95 in the 9-bump, 0.5mm-pitch micro SMD package, both in 1000-unit quantities.
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