LM4949
Stereo Class D Audio Subsystem with OCL Headphone
Amplifier
General Description
The LM4949 is a fully integrated audio subsystem designed
for stereo cell phone applications. The LM4949 combines a
2.5W stereo Class D amplifier plus a separate 190mW ste-
reo headphone amplifier, volume control, and input mixer
into a single device. The filterless class D amplifiers deliver
1.19W/channel into an 8Ω load with
<
1% THD+N from a 5V
supply. The headphone amplifier features National’s Output
Capacitor-less (OCL) architecture that eliminates the output
coupling capacitors required by traditional headphone ampli-
fiers. Additionally, the headphone amplifiers can be config-
ured with capacitively coupled (CC)loads, or used to drive an
external headphone amplifier. When configured for an exter-
nal amplifier, the V
DD
/2 output (VOC) controls the external
amplifier’s shutdown input.
For improved noise immunity, the LM4949 features fully
differential left, right and mono inputs. The three inputs can
be mixed/multiplexed to either the speaker or headphone
amplifiers. The left and right inputs can be used as separate
single-ended inputs, mixing multiple stereo audio sources.
The mixer, volume control, and device mode select are
controlled through an I
2
C compatible interface.
Output short circuit and thermal shutdown protection prevent
the device from being damaged during fault conditions. Su-
perior click and pop suppression eliminates audible tran-
sients on power-up/down and during shutdown.
Key Specifications
j
Efficiency V
DD
= 3.6V, 400mW into 8Ω 86.5%
j
Efficiency V
DD
= 5V, 1W into 8Ω 87.4%
j
Quiescent Power Supply Current
@
3.6V 9.36mA
j
Power Output at V
DD
=5V
Speaker:
R
L
=4Ω, THD+N ≤ 1%
R
L
=8Ω, THD+N ≤ 1%
R
L
=4Ω, THD+N ≤ 10%
2W
1.19W
2.5W
Headphone:
R
L
=16Ω, THD+N ≤ 1%
R
L
=32Ω, THD+N ≤ 1%
153mW
89mW
j
Shutdown Current 0.1µA
Features
n Output Short Circuit Protection
n Thermal Shutdown
n Stereo filterless Class D operation
n Selectable OCL/CC Headphone Drivers
n RF Suppression
n I
2
C Control Interface
n 32-step digital volume control
n Independent Speaker and Headphone Gain Settings
n Minimum external components
n Click and Pop suppression
n Micro-power shutdown
n Available in space-saving 25 bump µSMD package
Applications
n Mobile phones
n PDAs
n Laptops
Boomer
®
is a registered trademark of National Semiconductor Corporation.
September 2006
LM4949 Stereo Class D Audio Subsystem with OCL Headphone Amplifier
© 2006 National Semiconductor Corporation DS202001 www.national.com
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