LM4665 Datasheet, PDF (1/18 Pages) National Semiconductor (TI) – Filterless High Efficiency 1W Switching Audio Amplifier

December 2002
LM4665
Filterless High Efficiency 1W Switching Audio Amplifier
General Description
The LM4665 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 parts count,
simplifies circuit design, and reduces board area. The
LM4665 processes analog inputs with a delta-sigma modu-
lation technique that lowers output noise and THD when
compared to conventional pulse width modulators.
The LM4665 is designed to meet the demands of mobile
phones and other portable communication devices. Operat-
ing on a single 3V supply, it is capable of driving 8Ω trans-
ducer loads at a continuous average output of 400mW with
less than 2%THD+N.
The LM4665 has high efficiency with an 8Ω transducer load
compared to a typical Class AB amplifier. With a 3V supply,
the IC’s efficiency for a 100mW power level is 75%, reaching
80% at 400mW output power.
The LM4665 features a low-power consumption shutdown
mode. Shutdown may be enabled by either a logic high or
low depending on the mode selection. Connecting the Shut-
down Mode pin to either V_DD (high) or GND (low) enables
the Shutdown pin to be driven in a likewise manner to
activate shutdown.
The LM4665 has fixed selectable gain of either 6dB or 12dB.
The LM4665 has short circuit protection against a short from
the outputs to V_DD, GND or across the outputs.
Key Specifications
j Efficiency at 100mW into 8Ω transducer
75%(typ)
j Efficiency at 400mW into 8Ω transducer
80%(typ)
j Total quiescent power supply current (3V) 3mA(typ)
j Total shutdown power supply current (3V) 0.01µA(typ)
j Single supply range (MSOP & LD)
2.7V to 5.5V
j Single supply range (ITL) (Note 11)
2.7V to 3.8V
Features
n No output filter required for inductive transducers
n Selectable gain of 6dB (2V/V) or 12dB (4V/V)
n Very fast turn on time: 5ms (typ)
n User selectable shutdown High or Low logic level
n Minimum external components
n "Click and pop" suppression circuitry
n Micro-power shutdown mode
n Short circuit protection
n micro SMD, LLP, and MSOP packages (no heat sink
required)
Applications
n Mobile phones
n PDAs
n Portable electronic devices
Typical Application
20027001
FIGURE 1. Typical Audio Amplifier Application Circuit
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