LM4675 Datasheet, PDF (1/19 Pages) National Semiconductor (TI) – Ultra-Low EMI, Filterless, 2.65W, Mono, Class D Audio Power Amplifier with Spread Spectrum

August 2006
LM4675
Ultra-Low EMI, Filterless, 2.65W, Mono, Class D Audio
Power Amplifier with Spread Spectrum
General Description
The LM4675 is a single supply, high efficiency, 2.65W, mono,
Class D audio amplifier. A spread spectrum, filterless PWM
architecture reduces EMI and eliminates the output filter,
reducing external component count, board area consump-
tion, system cost, and simplifying design.
The LM4675 is designed to meet the demands of mobile
phones and other portable communication devices. Operat-
ing on a single 5V supply, it is capable of driving a 4Ω
speaker load at a continuous average output of 2.2W with
less than 1% THD+N. Its flexible power supply requirements
allow operation from 2.4V to 5.5V. The wide band spread
spectrum architecture of the LM4675 reduces EMI-radiated
emissions due to the modulator frequency.
The LM4675 has high efficiency with speaker loads com-
pared to a typical Class AB amplifier. With a 3.6V supply
driving an 8Ω speaker, the IC’s efficiency for a 100mW
power level is 80%, reaching 89% at 400mW output power.
The LM4675 features a low-power consumption shutdown
mode. Shutdown may be enabled by driving the Shutdown
pin to a logic low (GND).
The gain of the LM4675 is externally configurable which
allows independent gain control from multiple sources by
summing the signals. Output short circuit and thermal over-
load protection prevent the device from damage during fault
conditions.
Key Specifications
j Efficiency at 3.6V, 400mW into 8Ω speaker 89% (typ)
j Efficiency at 3.6V, 100mW into 8Ω speaker 80% (typ)
j Efficiency at 5V, 1W into 8Ω speaker
89% (typ)
j Quiescent current, 3.6V supply
2.2mA (typ)
j Total shutdown power supply current 0.01µA (typ)
j Single supply range
2.4V to 5.5V
j PSRR, f = 217Hz
82dB
Features
n Spread spectrum architecture reduces EMI
n Mono Class D Operation
n No output filter required for inductive loads
n Externally configurable gain
n Very fast turn on time: 17µs (typ)
n Minimum external components
n "Click and pop" suppression circuitry
n Micro-power shutdown mode
n Available in space-saving 0.5mm pitch micro SMD and
LLP packages
Applications
n Mobile phones
n PDAs
n Portable electronic devices
LM4675 Rf Emissions — 6in cable
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