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PDF LM4914 Data sheet ( Hoja de datos )
| Número de pieza | LM4914 | |
| Descripción | 1W Monaural/ 85mW Stereo Headphone Audio Amplifier | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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March 2003
LM4914
1W Monaural, 85mW Stereo Headphone Audio Amplifier
General Description
The unity-gain stable LM4914 is both a mono differential
output (for bridge-tied loads, or BTL) audio power amplifier
and a single-ended (SE) stereo headphone amplifier. Oper-
ating on a single 5V supply, the mono BTL mode delivers 1W
into an 8Ω load. In SE stereo mode, the amplifier delivers
85mW to 32Ω loads. The LM4914 features circuitry that
suppresses output transients ("clicks and pops").
The LM4914 is designed for notebook and other handheld
portable applications. It delivers high quality output power
from a surface-mount package and requires few external
components. The LM4914 is pin and functionally compatible
with the TPA0253.
Other features include an active-low micro-power shutdown
mode and thermal shutdown protection.
The LM4914 is available in a space efficient 10-lead
exposed-DAP TSSOP package.
Key Specifications
j BTL output power (RL = 8Ω)
VDD = at 3.0V, THD = 0.1%
VDD = at 5.0V, THD = 0.1%
j SE output power (RL = 32Ω)
VDD = at 3.0V, THD = 0.1%
VDD = at 5.0V, THD = 0.1%
330mW (typ)
1W (typ)
30mW (typ)
85mW (typ)
j Micro-power shutdown supply current
j PSRR (f = 1kHz)
VDD = at 3.0V, BTL Mode
VDD = at 5.0V, BTL Mode
0.03µA (typ)
52dB (typ)
52dB (typ)
Features
n Advanced "click and pop" suppression circuitry
n Stereo headphone amplifier mode
n Low current micro-power shutdown mode
n Thermal shutdown protection circuitry
n 2.5V to 5.5V operation
n Unity-gain stable
n Gain set with external resistors
n Space-saving exposed-DAP TSSOP package
Applications
n PDAs
n Cellular phones
n Handheld portable electronic devices
Connection Diagram
Top View
Order Number LM4914MH
See NS package Number MXF10A
200634A0
Boomer® is a registered trademark of National Semiconductor Corporation.
© 2003 National Semiconductor Corporation DS200634
www.national.com
1 page  
Electrical Characteristics: Bridged-Mode Operation (VDD = 3V) (Note 3)
The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for TA = 25˚C.
Symbol
Parameter
Conditions
PO
THD+N
VON
Output Power (Note 11)
Total Harmonic Distortion + Noise
Output Voltage Noise
THD = 0.1%, f = 1kHz
AV = 14dB, RL = 8Ω
f = 1kHz
PO = 250mW
CB = 0.47µF, 20Hz < f < 20kHz
LM4914
Typical
Limit
(Note 8) (Notes 9, 10)
330
0.2
Units
(Limits)
mW
%
29 µVRMS
Electrical Characteristics: SE Operation (VDD = 3V) (Note 3)
The following specifications apply for the circuit shown in Figure 1 and a measurement bandwidth of 20Hz to 80kHz, unless
otherwise specified. Limits apply for TA = 25˚C.
Symbol
Parameter
PO Output Power (Note 11)
VON Output Voltage Noise
Conditions
THD+N = 0.1%, f = 1kHz,
RL = 32Ω, AV = 1.9dB (Note 12)
CB = 0.47µF, 20Hz < f < 20kHz
LM4914
Typical
Limit
(Note 8) (Notes 9, 10)
30
13
Units
(Limits)
mW
µVRMS
Note 1: When operating on a 5VDC, an LM4914MH that has been properly mounted to a circuit board will deliver 1W into 8Ω. See the Application Information
sections for further information concerning PCB layout suggestions to maximize the LM4914MH’s output power into an 8Ω load.
Note 2: All voltages are measured with respect to the GND pin unless otherwise specified.
Note 3: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
functional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which
guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit
is given, however, the typical value is a good indication of device performance.
Note 4: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX, θJA, and the ambient temperature TA. The maximum
allowable power dissipation is PDMAX = (TJMAX–TA)/θJA or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4914, see power derating
curves for additional information.
Note 5: Human body model, 100pF discharged through a 1.5kΩ resistor.
Note 6: Machine Model, 220pF–240pF discharged through all pins.
Note 7: The given θJA is for an LM4914 packaged in an MH with the Exposed-DAP soldered to an exposed 2in2 area of 1oz printed circuit board copper.
Note 8: Typicals are measured at 25˚C and represent the parametric norm.
Note 9: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
Note 10: Datasheet minimum and maximum specification limits are guaranteed by design, test, or statistical analysis.
Note 11: Output power is measured at the amplifier’s package pins.
Note 12: See Application Information section "Single-Ended Output Power Performance and Measurement Considerations" for more information.
5 www.national.com
5 Page 
Application Information (Continued)
LM4914’s supply pins and ground. Do not substitute a ce-
ramic capacitor for the tantalum. Doing so may cause oscil-
lation.
Keep the length of leads and traces that connect capacitors
between the LM4914’s power supply pin and ground as
short as possible. Connecting a 0.47µF capacitor, CB, be-
tween the BYPASS pin and ground improves the internal
bias voltage’s stability and improves the amplifier’s PSRR.
The PSRR improvements increase as the bypass pin ca-
pacitor value increases. Too large, however, increases
turn-on time and can compromise the amplifier’s click and
pop performance. The selection of bypass capacitor values,
especially CB, depends on desired PSRR requirements,
click and pop performance (as explained in the section,
Proper Selection of External Components), system cost, and
size constraints.
MICRO-POWER SHUTDOWN
The LM4914 features an active-low micro-power shutdown
mode. When active, the LM4914’s micro-power shutdown
feature turns off the amplifier’s bias circuitry, reducing the
supply current. The logic threshold is typically VDD/2. The
low 0.03µA typical shutdown current is achieved by applying
a voltage to the SHUTDOWN pin that is as near to GND as
possible. A voltage that is greater than GND may increase
the shutdown current.
There are a few methods to control the micro-power shut-
down. These include using a single-pole, single-throw switch
(SPST), a microprocessor, or a microcontroller. When using
a switch, connect a 100kΩ pull-up resistor between the
SHUTDOWN pin and VDD and the SPST switch between the
SHUTDOWN pin and GND. Select normal amplifier opera-
tion by opening the switch. Closing the switch applies GND
to the SHUTDOWN pin, activating micro-power shutdown.
The switch and resistor guarantee that the SHUTDOWN pin
will not float. This prevents unwanted state changes. In a
system with a microprocessor or a microcontroller, use a
digital output to apply the active-state voltage to the SHUT-
DOWN pin.
HEADPHONE (SINGLE-ENDED) AMPLIFIER
OPERATION
BTL/SE [Mono (BTL)/Stereo (SE)] Function
Applying a voltage greater than 0.9VDD to the LM4914’s
BTL/SE headphone control pin switches the amplifier’s op-
eration from mono BTL to stereo SE. Applying a voltage less
than 0.55VDD to the LM4914’s BTL/SE headphone control
pin switches the amplifier’s operation from stereo SE to
mono BTL.
Figure 3 shows how to control the LM4914’s headphone
function using four external resistors and a dual-switch ste-
reo headphone jack. External resistors R4 - R6 provide the
control voltages that are applied through the upper head-
phone jack switch. R6 and R7 provide a DC return path for
the SE coupling capacitors.
200634A1
FIGURE 3. Headphone Operation and BTL - SE Mode Switching
With no headphones connected to the headphone jack, the
R5-R6 voltage divider sets the voltage applied to the BTL/SE
pin (pin 7) at approximately 50mV (comfortably below the
0.55VDD logic-low threshold). This 50mV tells the LM4914 to
select the signal applied to the MONO-IN input and places
the LM4914 in mono BTL operation. When stereo SE opera-
tion is desired, both headphone jack switches are opened
with a headphone plug. Opening the lower one allows R5 to
apply VDD to the BTL/SE pin. This switches the amplifier’s
inputs to the stereo signal. Opening the lower one breaks the
connection between AMP4’s output and the BTL speaker,
muting it. The output coupling capacitors block the amplifi-
er’s half supply DC voltage, protecting the headphones from
the VDD/2 DC output voltage.
Figure 3 also shows the suggested headphone jack electri-
cal connections. The jack is designed to mate with a three-
wire plug. The plug’s tip and adjacent ring should carry the
left and right channel stereo signals, respectively. The sleeve
furthest from the tip should carry the ground return. The
Switchcraft 35RAPC4BH3 five-terminal headphone jack
11 www.national.com
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet LM4914.PDF ] | |
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