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PDF LM4666SD Data sheet ( Hoja de datos )
| Número de pieza | LM4666SD | |
| Descripción | Filterless High Efficiency Stereo 1.2W Switching Audio Amplifier | |
| Fabricantes | National Semiconductor | |
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May 2004
LM4666
Filterless High Efficiency Stereo 1.2W Switching Audio
Amplifier
General Description
The LM4666 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
LM4666 processes analog inputs with a delta-sigma modu-
lation technique that lowers output noise and THD when
compared to conventional pulse width modulators.
The LM4666 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 450mW with
less than 1%THD+N. Its flexible power supply requirements
allow operation from 2.8V to 5.5V.
The LM4666 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 79%, reaching
84% at 450mW output power.
The LM4666 features a low-power consumption shutdown
mode. Shutdown may be enabled by driving the Shutdown
pin to a logic low (GND).
The LM4666 has fixed selectable gain of either 6dB or 12dB.
The LM4666 has short circuit protection against a short from
the outputs to VDD or GND.
Key Specifications
j Efficiency at 3V, 100mW into 8Ω transducer 79% (typ)
j Efficiency at 3V, 450mW into 8Ω transducer 84% (typ)
j Efficiency at 5V, 1W into 8Ω transducer 85% (typ)
j Total quiescent power supply current
7.0mA (typ)
j Total shutdown power supply current 0.02µA (typ)
j Single supply range
2.8V to 5.5V
Features
n No output filter required for inductive transducers
n Selectable gain of 6dB or 12dB
n Very fast turn on time: 6ms (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 SDA package
Applications
n Mobile phones
n PDAs
n Portable electronic devices
Typical Application
200558E6
FIGURE 1. Typical Audio Amplifier Application Circuit
Boomer® is a registered trademark of National Semiconductor Corporation.
© 2004 National Semiconductor Corporation DS200558
www.national.com
1 page  
External Components Description
(Figure 1)
Components
1. CS
2. CI
Functional Description
Supply bypass capacitor which provides power supply filtering. Refer to the Power Supply Bypassing
section for information concerning proper placement and selection of the supply bypass capacitor.
Input AC coupling capacitor which blocks the DC voltage at the amplifier’s input terminals.
Typical Performance Characteristics (Note 10)
THD+N vs Frequency
VDD = 5V, RL = 15µH + 8Ω + 15µH
POUT = 100mW/Channel, 30kHz BW
THD+N vs Frequency
VDD = 3V, RL = 15µH + 8Ω + 15µH
POUT = 100mW/Channel, 30kHz BW
20055827
THD+N vs Frequency
VDD = 3V, RL = 15µH + 4Ω + 15µH
POUT = 100mW/Channel, 30kHz BW
20055826
THD+N vs Output Power/Channel
VDD = 5V, RL = 15µH + 8Ω + 15µH
f = 1kHz, 22kHz BW
20055825
5
20055830
www.national.com
5 Page 
Application Information (Continued)
typical value. Increased THD may also be observed with
voltages less than VDD on the Shutdown pin when in PLAY
mode.
The LM4666 has an internal resistor connected between
GND and Shutdown pins. The purpose of this resistor is to
eliminate any unwanted state changes when the Shutdown
pin is floating. The LM4666 will enter the shutdown state
when the Shutdown pin is left floating or if not floating, when
the shutdown voltage has crossed the threshold. To mini-
mize the supply current while in the shutdown state, the
Shutdown pin should be driven to GND or left floating. If the
Shutdown pin is not driven to GND, the amount of additional
resistor current due to the internal shutdown resistor can be
found by Equation (1) below.
(VSD - GND) / 60kΩ
(1)
With only a 0.5V difference, an additional 8.3µA of current
will be drawn while in the shutdown state.
GAIN SELECTION FUNCTION
The LM4666 has fixed selectable gain to minimize external
components, increase flexibility and simplify design. For a
differential gain of 6dB, the Gain Select pin should be per-
manently connected to VDD or driven to a logic high level.
For a differential gain of 12dB, the Gain Select pin should be
permanently connected to GND or driven to a logic low level.
The gain of the LM4666 can be switched while the amplifier
is in PLAY mode driving a load with a signal without damage
to the IC. The voltage on the Gain Select pin should be
switched quickly between GND (logic low) and VDD (logic
high) to eliminate any possible audible artifacts from appear-
ing at the output. For typical threshold voltages for the Gain
Select function, refer to the Gain Threshold Voltages graph
in the Typical Performance Characteristics section.
11 www.national.com
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