Analogue, Mixed Signal, LSI


Headphone amp operates down to 0,9 V

10 March 2004 Analogue, Mixed Signal, LSI

Maxim has extended its DirectDrive headphone amplifier series with the introduction of the MAX9721A/B/C devices. The MAX9721 operates from a 0,9 to 1,8 V single supply, allowing the device to be powered directly from a single AA or AAA battery.

These headphone amps employ a ground-referenced output from a single supply, eliminating the two bulky DC-blocking capacitors typically required between the amplifier and headphone. Eliminating the DC-blocking capacitors also improves the low-frequency response, allowing full-range audio reproduction - especially important for music playback.

The MAX9721 is ideal for single-cell portable audio equipment. Like Maxim's other DirectDrive headphone amps, it does not require a DC bias voltage to be applied to the headphone-jack ground pin, thus simplifying end-product design and reliability.

An 80 dB at 1 kHz power-supply rejection ratio allows the devices to operate from noisy digital supplies without an additional linear regulator. They consume only 2,2 mA of supply current, has short-circuit and thermal-overload protection, and is specified over -40 to +85°C. Internal fixed gains of -2 V/V (MAX9721A), -1,5 V/V (MAX9721B), and -1 V/V (MAX9721C) further reduce external component count.

The devices deliver 20 mW per channel into a 32 Ω load with VDD of 1,5 V. The typical THD+N is 0,006% and the outputs include ±8 kV ESD protection. Comprehensive click-and-pop circuitry suppresses audible clicks and pops on start-up and shutdown. A low-power shutdown mode reduces supply current to 1,0 µA to extend battery life. The MAX9721 is available in a tiny 12-bump (1,54 x 2,02 x 0,6 mm) UCSP and a 12-pin (4 x 4 x 0,8 mm) TQFN package.



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