參數資料
型號: LM4868MTEX/NOPB
廠商: NATIONAL SEMICONDUCTOR CORP
元件分類: 音頻/視頻放大
英文描述: 3 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO20
封裝: 6.50 X 4.40 MM, 0.90 MM HEIGHT, EXPOSED PAD, PLASTIC, TSSOP-20
文件頁數: 5/28頁
文件大?。?/td> 792K
代理商: LM4868MTEX/NOPB
Application Information (Continued)
STEREO-INPUT MULTIPLEXER (STEREO MUX)
The LM4868 has two stereo inputs. The MUX CTRL Pin
controls which stereo input is active. As shown in the Truth
Table for Logic Inputs, applying 0V to the MUX CTRL input
activates stereo input 1, whereas applying V
DD to the MUX
CTRL inputs activates stereo input 2. To ensure correct
amplifier operation, unused MUX inputs should be tied to
GND.
Typical LM4868 applications use the MUX to switch between
two stereo input signals. Each stereo channel’s gain can be
tailored to produce the required output signal level by choos-
ing the appropriate input and feedback resistor ratio.
Another configuration uses the MUX to select two different
gains or frequency compensated gains that amplify a single
pair of stereo input signals. Figure 5 shows two different
feedback networks, Network 1 and Network 2. Network 1
produces increasing gain as the input signal’s frequency
decreases. This can be used to compensate a small,
full-range speaker’s low frequency response roll-off. Network
2 sets the gain for an alternate load such as headphones.
The circuit in Figure 6 uses Network 1 when driving external
speakers, switching to Network 2 when headphones are
connected. The normally closed control switch in Figure 6’s
headphone jack connects to the MUX CTRL pin. When
headphones are connected, the LM4868’s internal pull-up
that applies V
DD to the HP-IN and the external 100k
resis-
tor applies V
DD to MUX CTRL pin. Simultaneously applying
these control voltages automatically selects the amplifier
(headphone or bridge) and switches the gain (MUX channel
selection). Alternatively, leaving the MUX CTRL pin indepen-
dently accessible allows a user to select bass boost as
needed. This alternative user-selectable bass-boost scheme
requires connecting equal ratio resistor feedback networks
to each MUX input channel. The value of the resistor in the
RC network is chosen to give a gain that is necessary to
achieve the desired bass-boost.
Switching between the MUX channels may change the input
signal source or the feedback resistor network. During the
channel switching transition, the average voltage level
20026731
FIGURE 4. Typical Audio Amplifier Application Circuit
(Pin out shown for the 24-pin Exposed-DAP LLP package. Numbers in ( ) are for the 20-pin MTE and MT packages.)
20026728
FIGURE 5. Input MUX Example
LM4868
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相關PDF資料
PDF描述
LM4868MT/NOPB 1.5 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO20
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