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PDF LM4894LD Data sheet ( Hoja de datos )
| Número de pieza | LM4894LD | |
| Descripción | 1 Watt Fully Differential Audio Power Amplifier With Shutdown Select | |
| Fabricantes | National Semiconductor | |
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June 2003
LM4894
1 Watt Fully Differential Audio Power Amplifier With
Shutdown Select
General Description
The LM4894 is a fully differential audio power amplifier
primarily designed for demanding applications in mobile
phones and other portable communication device applica-
tions. It is capable of delivering 1 watt of continuous average
power to an 8Ω BTL load with less than 1% distortion
(THD+N) from a 5VDC power supply.
Boomer audio power amplifiers were designed specifically to
provide high quality output power with a minimal amount of
external components. The LM4894 does not require output
coupling capacitors or bootstrap capacitors, and therefore is
ideally suited for mobile phone and other low voltage appli-
cations where minimal power consumption is a primary re-
quirement.
The LM4894 features a low-power consumption shutdown
mode. To facilitate this, Shutdown may be enabled by either
logic high or low depending on mode selection. Driving the
shutdown mode pin either high or low enables the shutdown
select pin to be driven in a likewise manner to enable Shut-
down. Additionally, the LM4894 features an internal thermal
shutdown protection mechanism.
The LM4894 contains advanced pop & click circuitry which
eliminates noises which would otherwise occur during
turn-on and turn-off transitions.
The LM4894 is unity-gain stable and can be configured by
external gain-setting resistors.
j Power Output at 5.0V & 1% THD
j Power Output at 3.3V & 1% THD
j Shutdown Current
1.0W(typ)
400mW(typ)
0.1µA(typ)
Features
n Fully differential amplification
n Available in space-saving packages micro SMD, MSOP,
and LLP
n Ultra low current shutdown mode
n Can drive capacitive loads up to 500pF
n Improved pop & click circuitry eliminates noises during
turn-on and turn-off transitions
n 2.2 - 5.5V operation
n No output coupling capacitors, snubber networks or
bootstrap capacitors required
n Unity-gain stable
n External gain configuration capability
n Shutdown high or low selectivity
n High CMRR
Applications
n Mobile phones
n PDAs
n Portable electronic devices
Key Specifications
j Improved PSRR at 217Hz
80dB(typ)
Connection Diagrams
Mini Small Outline (MSOP) Package
LLP Package
20013723
Top View
Order Number LM4894MM
See NS Package Number MUB10A
Boomer® is a registered trademark of National Semiconductor Corporation.
© 2003 National Semiconductor Corporation DS200137
20013735
Top View
Order Number LM4894LD
See NS Package Number LDA10B
www.national.com
1 page  
Typical Performance Characteristics
LD Specific Characteristics
LM4894LD
THD+N vs Output Power
VDD = 5V, 4Ω RL
LM4894LD
THD+N vs Frequency
VDD = 5V, 4Ω RL, and Power = 1W
LM4894LD
Power Dissipation vs
Output Power
20013790
20013791
LM4894LD
Power Derating Curve
20013792
20013793
5 www.national.com
5 Page 
Typical Performance Characteristics
Non-LD Specific Characteristics (Continued)
PSRR vs
DC Common-Mode Voltage
PSRR vs
DC Common-Mode Voltage
20013780
THD vs
Common-Mode Voltage
THD vs
Common-Mode Voltage
20013781
20013782
20013783
Application Information
DIFFERENTIAL AMPLIFIER EXPLANATION
The LM4894 is a fully differential audio amplifier that fea-
tures differential input and output stages. Internally this is
accomplished by two circuits: a differential amplifier and a
common mode feedback amplifier that adjusts the output
voltages so that the average value remains VDD/2. When
setting the differential gain, the amplifier can be considered
to have "halves". Each half uses an input and feedback
resistor (Ri1and RF1) to set its respective closed-loop gain
(see Figure 1). With Ri1 = Ri2 and RF1 = RF2, the gain is set
at -RF/Ri for each half. This results in a differential gain of
AVD = -RF/Ri
(1)
It is extremely important to match the input resistors to each
other, as well as the feedback resistors to each other for best
amplifier performance. See the Proper Selection of Exter-
nal Components section for more information. A differential
amplifier works in a manner where the difference between
the two input signals is amplified. In most applications, this
would require input signals that are 180˚ out of phase with
each other. The LM4894 can be used, however, as a single
ended input amplifier while still retaining its fully differential
benefits. In fact, completely unrelated signals may be placed
on the input pins. The LM4894 simply amplifies the differ-
ence between them. Figures 2 and 3 show single-ended
applications of the LM4894 that still take advantage of the
differential nature of the amplifier and the benefits to PSRR,
common-mode noise reduction, and "click and pop" reduc-
tion.
All of these applications, either single-ended or fully differ-
ential, provide what is known as a "bridged mode" output
(bridge-tied-load, BTL). This results in output signals at Vo1
and Vo2 that are 180˚ out of phase with respect to each
11 www.national.com
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| PDF Descargar | [ Datasheet LM4894LD.PDF ] | |
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