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National Semiconductor Corporation (NS) has announced two Boomer® Class AB amplifiers featuring a micro SMD package with a 0.4mm pitch, making it the world's smallest audio amplifier. The LMW1 1.25W audio amplifier and the LM4985 stereo headphone amplifier offer the advantages of low quiescent current and high output power, as well as extended battery life for MP3 players, mobile phones and other portable electronics.National's 0.4mm pitch package occupies very little board space on the printed circuit board, so even if board space is limited, engineers can easily complete the line design. National Semiconductor introduced the advanced micro SMD package in 1999 and later developed a new generation of micro SMD packages with a pitch of only 0.4mm. In addition to the advanced process technology necessary to produce silicon chips, the new package also introduces a new generation of soldering and silicon substrate grinding technology.
The 1.2W Class AB audio amplifier, model LM4941, incorporates National's proprietary RF signal suppression circuitry, which has the advantage of suppressing RF interference and is 20dB better than existing designs. The output of the amplifier, like an antenna, also has its own receiving capability, which not only automatically receives external noise, but also transmits it back to the signal path of the amplifier. If the amplifier has a built-in RF suppression circuit, it can prevent external noise from being received at the output. This 1.2mm x 1.2mm fully differential amplifier eliminates common mode noise common to most systems and has a quiescent current of only 1.7mA when operated from a 5V supply.
The LM4985 low-noise stereo headphone amplifier features a 32-step non-linear volume control controlled via an I2C-compatible interface, eliminating the need for software to increase the system's volume control resolution. The volume control curve is specially designed to meet the human hearing sensitivity, and the user can listen more comfortably. When the amplifier is in the output-free capacitor mode, the quiescent current of the two channels is as low as 3mA. If operated with 5V, it can provide an average output power of up to 135mW per channel for 16W load.
The LM4985 is designed for flexibility and is designed for capacitive coupling or output capacitorless (OCL) designs. In addition, vendor customers can even use the same National Semiconductor amplifier to develop different platforms to enable new products to be certified faster.
Operating from a 5V power supply, the LM4941 can continuously deliver an average of 1.25W of power, driving an 8W load with a total harmonic distortion and noise (THD+N) of only 0.04%. If the input noise is 217Hz, the chip's power supply rejection ratio (PSRR) is as high as 95dB (typ). If the input noise is 1kHz, the signal-to-noise ratio is as high as 108dB. In addition, this amplifier also features a mono speaker output.
Operating at 3.6V and the total harmonic distortion is set to 1%, the LM4985 can provide an average of up to 68mW of output power per channel, driving a 16W load, and if no output capacitor mode is used, Provides 38mW of output power per channel and drives a 32W load. In addition, the chip features I2C-compatible volume control, allowing engineers to set gain from a wide range of 18dB to -76dB. If the volume is extremely low, the volume must have a large change, and human hearing will be noticed. Therefore, this chip has adapted to this low-volume characteristic, and the lifting range of each step is increased. If the volume is large, even if there is a small change in the volume, human hearing is easy to detect, so this chip will also reduce the level of each level of the large volume. With a no-output capacitor mode and an input noise of 217 Hz, the chip's power supply rejection ratio is 77 dB.
Both chips do not require an output coupling capacitor or start capacitor, and have internal thermal shutdown protection. In addition, the two chips also feature advanced switching/switching noise suppression circuitry to eliminate noise generated during on/off.
The LM4985 chip is priced at $1.46 each, while the LM4941 chip is priced at $0.62 each. Both chips are priced at 1,000 units and are available in stock.
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