LM4670_06 Datasheet, PDF (1/20 Pages) National Semiconductor (TI) – Filterless High Efficiency 3W Switching Audio Amplifier

July 2006
LM4670
Filterless High Efficiency 3W Switching Audio Amplifier
General Description
The LM4670 is a fully integrated single-supply high efficiency
switching audio amplifier. It features an innovative modulator
that eliminates the LC output filter used with typical switching
amplifiers. Eliminating the output filter reduces external com-
ponent count, simplifies circuit design, and reduces board
area. The LM4670 processes analog inputs with a delta-
sigma modulation technique that lowers output noise and
THD when compared to conventional pulse width modula-
tors.
The LM4670 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 2.3W with
less than 1% THD+N. Its flexible power supply requirements
allow operation from 2.4V to 5.5V.
The LM4670 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 77%, reaching 88% at 600mW output power.
The LM4670 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 LM4670 is externally configurable which
allows independent gain control from multiple sources by
summing the signals.
Key Specifications
j Efficiency at 3.6V, 100mW into 8Ω speaker 77% (typ)
j Efficiency at 3.6V, 600mW into 8Ω speaker 88% (typ)
j Efficiency at 5V, 1W into 8Ω speaker
87% (typ)
j Quiescent current, 3.6V supply
4.8mA (typ)
j Total shutdown power supply current 0.01µA (typ)
j Single supply range
2.4V to 5.5V
Features
n No output filter required for inductive loads
n Externally configurable gain
n Very fast turn on time: 1.35ms (typ)
n Minimum external components
n "Click and pop" suppression circuitry
n Micro-power shutdown mode
n Short circuit protection
n Available in space-saving microSMD and LLP packages
Applications
n Mobile phones
n PDAs
n Portable electronic devices
Typical Application
20089901
FIGURE 1. Typical Audio Amplifier Application Circuit
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