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參數(shù)資料
| 型號(hào)： | MXF10A |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | 1W Monaural, 85mW Stereo Headphone Audio Amplifier |
| 中文描述： | 1W的單聲道，85mW立體聲耳機(jī)音頻放大器 |
| 文件頁數(shù)： | 11/15頁 |
| 文件大?。?/td> | 384K |
| 代理商： | MXF10A |
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, C
, 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 C
, 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 V
/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 100k
pull-up resistor between the
SHUTDOWN pin and V
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 0.9V
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 0.55V
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.
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
0.55V
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 V
DD
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 V
DD
/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
200634A1
FIGURE 3. Headphone Operation and BTL - SE Mode Switching
L
www.national.com
11
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