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National Semiconductor Corporation has announced three stereo headphone amplifiers with ground reference as an advantage, eliminating the need for external DC blocking capacitors, making them ideal for portable music players, mobile phones, CD players, personal digital assistants, media players, laptops and other portable electronics.
The LM4920 chip is a fixed-gain headphone amplifier that eliminates the need for an output capacitor and is 67% smaller than the previous generation LLP® package due to its 2mm x 2mm micro SMD package. In addition, the chip also has low logic level operation capability, which can be easily used with low voltage digital integrated circuits.
Another chip, model LM4981, is based on the core of National's LM4920 chip, with the addition of high/low volume tuning, eliminating the need for complex software to regulate volume.
The LM4982 chip can be adjusted with digital control technology via an I2C-compatible interface. The chip also features a headphone sensing function that can be judged by sensing to determine whether the output jack is plugged into a mono or stereo headset.
The headphone amplifier chip uses a low-noise inverting charge pump to provide a negative supply voltage, so that the output can be grounded as a reference voltage instead of a conventional headphone amplifier, with a nominal DC voltage as a reference, so there is no need An output coupling capacitor is added to drive the single-ended load. This amplifier technology helps reduce the number of components required, saves system cost and shrinks the board, and improves the low frequency response of the headphone output.
Main features and advantages
The LM4920 can be powered by 3V, continuously outputting an average of 80mW, driving a 16W single-ended load, or ensuring 40mW per channel, driving a 16W load with less than 1% total harmonic distortion and noise. Since the typical gain of 1.5V is internally fixed, there is no need to add an external resistor to set the gain. If the input noise is 217Hz, the chip's power supply rejection ratio (PSRR) can reach 70dB (typical). In addition to internal thermal shutdown protection, the chip also features a low-power shutdown mode that can be used to turn off any channel by using the logic low function to drive the shutdown channel pin. The LM4920 also has fixed logic levels to better match the operation of low voltage baseband processors and microprocessors.
The LM4981 can supply up to 83mW of continuous power with a 3V supply, driving a 16W load with less than 1% total harmonic distortion and noise. The chip can be operated from a 2V to 4.2V power supply and features high/low volume control to set the gain of the amplifier with a two-wire interface with a gain range from -33dB to +12dB. Divided into 16 steps step by step. The chip features high/low active two low power shutdown modes for flexible control of shutdown. If the input noise is 217Hz, the chip's power supply rejection ratio can reach 67dB (typ).
The LM4982 is a variable gain amplifier featuring a 3V supply, continuous output of up to 80mW, driving a 16W single-ended load, or ensuring 40mW per channel and driving a 16W load. Harmonic distortion and noise will not exceed 1%. If the input noise is 1kHz, the chip's power supply rejection ratio can reach 66dB (typ). In addition, because the chip also features I2C compatible volume control, the gain can be set between 18dB and -76dB.
All of the above chips have built-in advanced switching/switching noise suppression circuits to help eliminate the noise generated during on/off.
Price and availability
The LM4920 is available in a 14-bump micro SMD package and is priced at $0.89 each.
The LM4981 is available in a 16-pin LLP® package and is priced at $1.15 each.
The LM4982 is available in a 16-bump micro SMD package and is priced at $1.50 each.
All of the above three chips are purchased in 1,000 units and are available in large quantities.
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