audio/videoZONE Products for the week of July 8, 2002
Maxim Integrated Products Says . . .
MAX4410: Headphone Amplifier Eliminates Bulky Dc-Blocking
Capacitors
Maxim Integrated Products introduced the MAX4410 DirectDrive stereo headphone
amplifier. The MAX4410 employs a revolutionary architecture that produces
a ground-referenced output from a single supply, eliminating the two bulky
DC-blocking capacitors that are typically required between the amplifier
and headphone. The design produces the world's lowest profile, smallest
amplifier solution, occupying eight times less overall board space than
existing designs. The MAX4410 is ideal for portable audio equipment where
board space and height are critical. Unlike previous solutions, the MAX4410
does not require a DC bias voltage to be applied to the headphone jack ground
pin, significantly simplifying end product design and reliability.
The MAX4410 operates from a single 1.8V to 3.6V supply, produces 80mW
per channel into a 16-ohm load, and has only 0.005% THD + N. High, 90dB
PSRR allows the part to operate directly from noisy supplies. Independent
left and right low-power shutdown controls make it possible to optimize
power savings in mixed-mode mono/stereo applications. In addition to minimizing
size, eliminating the DC-blocking capacitors also improves the low-frequency
response of the amplifier, allowing full-range audio reproduction-especially
important for music and video playback. Comprehensive click-and-pop reduction
circuitry ensures fast turn-on/turn-off times without audible glitches.
The outputs include ±8kV ESD protection.
analogZone Says . . .
It has been really frustrating knowing this part was on the way, but having to wait for the press release to hit the web. Finally there is a product that is completely safe -- rather than just "mostly safe" -- that can be used without a dc blocking capacitor on each of the headphone outputs. The technique is certainly not new, using a charge pump to produce a complementary negative supply, but the application is well aimed. Instead of having the audio output biased around about half the supply voltage we have, instead, bias around the mid-point of the positive supply and the created negative rail -- i.e. ground. The dynamic range is also effectively doubled. The charge pump requires a couple of capacitors, to be sure, but those are now small ceramics instead instead of large tantalums (if you want any low-frequency output at all.)
The charge pump operates at about 320 kHz switching frequency -- well beyond audio -- with deliberately slowed turn-on/turn-off times to reduce di/dt noise. Three 2.2 uF ceramics are required, one for the charge pump, and one to decouple each rail. Increasing the size of the charge pump capacitor can further reduce di/dt noise if required. Removing the output capacitors already removes one source of audio "pops" but additional suppression is provided with power-up and power-down voltage control.
The supply voltage for this stereo headphone amplifier is a nominal 3 V and quiescent is a typical 7 mA with both channels enabled. PSRR is a typical 90 dB, while the 1% THD+N levels are reached at 65 mW into 32 ohms and 80 mW into 16 ohms, more than respectable enough numbers for headphone use. At more realistic numbers for power into an ear, 50 mW into 16 ohms produces a THD+N of typically 0.005%. At those sorts of levels SNR is down at 95 dB (at 1 kHz.) Gain flatness extends well beyond audio frequencies. Either, or both, audio channels can be shut down independently, while there is also short-circuit and overload protection.
This is the first stereo headphone amplifier to be offered that is really biased around zero volts and which requires no specially-insulated headphone jack. It is priced to sell in vast quantities, which it will do into all sorts of portable equipment, both entertainment devices and communications devices such as cell phones, notebooks and PDAs.
The MAX4410 is in production in chip-scale (14-bump UCSP 2 mm x 2 mm)
and a TSSOP-16, priced at $0.75 in 100-k piece lots. An evaluation kit is
available.
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