LM4981 Datasheet, PDF (1/18 Pages) National Semiconductor (TI) – Ground-Referenced, 80mW Stereo Headphone Amplifier with Digital Volume Control

November 2005
LM4981
Ground-Referenced, 80mW Stereo Headphone Amplifier
with Digital Volume Control
General Description
The LM4981 is a stereo, ground-referenced, output
capacitor-less headphone amplifier capable of delivering
83mW of continuous average power into a 16Ω load with
less than 1% THD+N while operating from a single 3V
supply.
The LM4981 features a new circuit technology that utilizes a
charge pump to generate a negative reference voltage. This
allows the outputs to be biased about ground, thereby elimi-
nating output-coupling capacitors typically used with normal
single-ended loads.
The LM4981 provides high quality audio reproduction with
minimal external components. A ground referenced output
eliminates the output coupling capacitors typically required
to drive single-ended loads such as headphones. The
ground reference architecture reduces components count,
cost and board space consumption, making the LM4981
ideal for handheld MP3 players, mobile phones and other
portable equipment where board space is at a premium.
Eliminating the output capacitors also improves low fre-
quency response.
The LM4981 operates from a single 2.0V – 4.2V supply, and
features a 2-wire, up/down volume control that sets the gain
of the amplifier between -33dB to +12dB in 16 discrete
steps. Selectable (active high/low) low power shutdown
mode provides flexible shutdown control. Superior click and
pop suppression eliminates audible transients during
start-up and shutdown.
The LM4981 features an Automatic Standby Mode circuitry
(patent pending). In the absence of an input signal, after
approximately 12 seconds, the LM4981 goes into low cur-
rent standby mode. The LM4981 recovers into full power
operating mode immediately after a signal is applied to either
the left or right input pins. This feature saves power supply
current in battery operated applications.
Key Specifications
j Improved PSRR at 217Hz
j THD+N at 1kHz, 50mW
into 32Ω SE (3V)
j Single Supply Operation (V_DD)
j Power Output at VDD = 3V,
RL = 16Ω, THD ≤ 1%
j Shutdown Current
67dB (typ)
1.0% (typ)
2.0 to 4.2V
83mW (typ)
0.01µA (typ)
Features
n Ground Referenced Outputs
n No Output Coupling Capacitors
n 16-Step Volume Control
n Auto-Standby Mode
n High PSRR
n Available in Space Saving LLP package
n Low Power Shutdown Mode
n Improved Click and Pop Suppression Eliminates Noises
During Turn-on and Turn-off Transients
n 2.0V to 4.2V Operation
n 83mW Per Channel Into 16Ω
n Selectable Shutdown Controls (Active High/Low)
Applications
n Portable MP3 Players
n Mobile Phones
n PDAs
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© 2005 National Semiconductor Corporation DS201473
www.national.com