LM49250 Datasheet, PDF (1/36 Pages) National Semiconductor (TI) – Enhanced Emissions Suppression Stereo Class D Audio Sub-System with Ground Referenced Headphone Amplifier and Mono Earpiece

September 19, 2008
LM49250 
Enhanced Emissions Suppression Stereo Class D Audio
Sub-System with Ground Referenced Headphone
Amplifier and Mono Earpiece
General Description
The LM49250 is a fully integrated audio subsystem designed
for stereo cell phone applications. The LM49250 combines a
2.4W/Ch stereo class D speaker amplifiers with a 45mW/Ch
stereo ground referenced headphone amplifier, a class AB
earpiece amplifier, National 3D enhancement, volume con-
trol, and an input mixer into a single device. The filterless class
D amplifiers deliver 1.2W/Ch into an 8Ω load with <1% THD
+N from a 5V supply.
The LM49250 features a new circuit technology that utilizes
a charge pump to generate a negative supply voltage. This
allows the headphone outputs to be biased about ground,
thereby eliminating the output-coupling capacitors.
For improved noise immunity, the LM49250 features fully dif-
ferential left, right and mono inputs. The three inputs can be
mixed/multiplexed to any output combination of the loud-
speaker, headphone or earpiece amplifiers. The left and right
differential inputs can be used as separate single-ended in-
puts, mixing multiple stereo audio sources. The mixer, volume
control, and device mode select are controlled through an
I²C compatible interface.
Output short circuit and thermal overload protection prevent
the device from being damaged during fault conditions. Su-
perior click and pop suppression eliminates audible transients
on power-up/down and during shutdown.
Key Specifications
■ Power Output at V_DD = 5V
Speaker:
R_L = 4Ω, THD+N ≤ 1%
R_L = 4Ω, THD+N ≤ 10%
R_L = 8Ω, THD+N ≤ 1%
Headphone:
R_L = 16Ω, THD+N ≤ 1%
R_L = 32Ω, THD+N ≤ 1%
Earpiece:
R_L = 16Ω, THD+N ≤ 1%
R_L = 32Ω, THD+N ≤ 1%
■ Shutdown Current
■ Efficiency at 5V, 1W into 8Ω
■ Efficiency at 3.6V, 500mW into 8Ω
1.97W/Ch
2.4W/Ch
1.2W/Ch
41mW/Ch
45mW/Ch
170mW
90mW
0.1μA
87%
85%
Features
■ ^{Output Short Circuit Protection}
■ ^{Thermal Overload Protection}
■ ^{Stereo filterless Class D operation}
■ ^{Spread spectrum modulation}
■ ^{Ground referenced Headphone Drivers}
■ ^{I2C Control Interface}
■ ^{32-step input volume control}
■ ^{Output volume control}
■ ^{Minimum external components}
■ ^{Click and Pop suppression}
■ ^{Micro-power shutdown}
■ ^{Available in space-saving 36–bump µSMD package}
■ ^{Single supply operation}
■ ^{RF suppression}
Applications
■ ^{Mobile phones}
■ ^{Portable Navigation Devices}
■ ^{Portable Media Players}
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