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參數(shù)資料
| 型號： | 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)： | 9/15頁 |
| 文件大?。?/td> | 384K |
| 代理商： | MXF10A |
Application Information
BRIDGE (BTL) OR SINGLE-ENDED (SE)
CONFIGURATION EXPLANATION
As shown in
Figure 2
, the LM4914 consists of one input
multiplexer (MUX) and two power amplifiers designed to
drive loads that have a minimum impedance of 4
. In mono
BTL mode, AMP1 and AMP2 drive a speaker connected
between their outputs. In stereo SE mode, AMP1 and AMP2
each drive a SE load such as stereo headphones.
In mono BTL mode, R1 works with one of AMP1’s internal
62.5kW feedback resistors to set this amplifier’s gain. AMP2
operates unity gain, set by two internal 20k
resistors. In
stereo SE modes, R2 and R3 work with AMP1’s and AMP2’s
internal 62.5k
feedback resistors to set each amplifier’s
gain. The LM4914 drives a BTL load, such as a speaker,
connected between AMP1’s and AMP2’s outputs. Two SE
loads can also be connected to the LM4914’s outputs, one
driven by AMP1 and the other driven by AMP2.
When the LM4914 operates in BTL mode, AMP1’s output
serves as AMP2’s input through AMP2’s input MUX. This
results in AMP1 and AMP2 producing signals identical in
magnitude, but 180 out of phase. Taking advantage of this
phase difference, a load placed between ROUT/M+ and
LOUT/M- is driven differentially (commonly referred to as
"bridge mode"). This results in a differential, or BTL, gain of
A
V
(BTL) = -2(A
V
(SE))
A
V
(SE) = -2(62.5k
) / R
i
A
V
(BTL) = -125k
/ R
i
(1)
Bridge mode amplifiers are different from single-ended am-
plifiers that drive loads connected between a single amplifi-
er’s output and ground. At any given supply voltage, bridge
mode has a distinct advantage over the single-ended con-
figuration: its differential output doubles the voltage swing
across the load. Theoretically, this produces four times the
output power when compared to a single-ended, capacitively
coupled amplifier under the same conditions. This increase
in attainable output power assumes that an amplifier is not
current limited and that the output signal is not clipped. To
ensure minimum output signal clipping when choosing an
amplifier’s closed-loop gain, refer to the Audio Power Ampli-
fier Design section.
POWER DISSIPATION
Power dissipation is a major concern when designing a
successful single-ended or bridged amplifier. Equation (2)
states the maximum power dissipation point for a single-
ended amplifier operating at a given supply voltage and
driving a specified output load.
P
DMAX-SE
= (V
DD
)
2
/ 2
π
2
R
L
:
However, a direct consequence of the increased power de-
livered to the load by a bridge amplifier is higher internal
power dissipation for the same conditions. The LM4914 has
two operational amplifiers driving a mono bridge load. The
maximum internal power dissipation operating in the bridge
mode is twice that of a single-ended amplifier. From Equa-
tion (3), assuming a 5V power supply and an 8
load, the
maximum BTL-mode power dissipation is 158mW.
Single-Ended
(2)
200634C3
FIGURE 2. Typical Audio Amplifier Application Circuit
L
www.national.com
9
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