Audio amps have high PSU rejection for cellphones

New from National Semiconductor, the LM4894 and LM4895 Boomer audio amplifiers are optimised for the cellular phone market, and are said to have the best PSRR performance available.

New from National Semiconductor, the LM4894 and LM4895 Boomer audio amplifiers are optimised for the cellular phone market, and are said to have the best PSRR performance available in the industry.

Improved PSRR (power supply rejection ratio) performance reduces the effect of noise on power supply lines being picked up and intensified by the audio amplifier.

As a result, there is less noise to the earpiece speaker in cellular phone applications.

Higher PSRR also eliminates the need for additional components to condition the power supply lines.

The LM4894 and LM4895 are designed for use in cellular phones, PDAs and other portable electronic devices.

"National has the number one market share in audio amplifiers for the cellular market", said Hector Hernandez, marketing manager for National's audio amplifier product line.

"These new Boomer amplifiers will enable our customers to make cellular phones with sharper, clearer audio quality.

The fully-differential design of the LM4894 and LM4895 allows them to deliver the best possible PSRR performance available in an audio amplifier for the cellular market".

With the input terminated with a 10ohm resistive load, the LM4894/95 deliver 80dB PSRR at 217Hz at 3V.

With the input unterminated (floating), the LM4894/95 deliver 87dB PSRR at 217Hz at 3V.

They also deliver 50dB of CMRR (common mode rejection ratio), a specification not possible in typical BTL configuration amplifiers.

An additional feature of the LM4894 and LM4895 is the selectable shutdown mode.

This allows designers to select either shutdown logic high or shutdown logic low.

The LM4894/95 have been optimised to save power by operating at a low supply voltage (3V), while still providing sufficient output power (350mW, 8ohm, less than 1%THD), suitable for normal listening and speakerphone and ringer tone amplification.

Because of the fully differential design of the LM4894, the input coupling capacitor is eliminated, thereby reducing pop and click noise at turn-on and turn-off.

This device also offers an external gain configuration capability and has an internal thermal shutdown protection mechanism.

The LM4895's fully differential design and 6dB fixed gain bring the simplest audio amplifier solution available in the market.

This device eliminates all of the external components required, except for one external capacitor, saving the customer design and manufacturing time, board space, component count and costs.

Back to top