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參數(shù)資料
| 型號(hào)： | LM4835MWC |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻控制 |
| 英文描述： | 2 CHANNEL(S), VOLUME CONTROL CIRCUIT, UUC |
| 封裝： | WAFER |
| 文件頁數(shù)： | 5/26頁 |
| 文件大小： | 858K |
| 代理商： | LM4835MWC |
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Application Information (Continued)
the pop is directly proportional to the input capacitor’s size.
Higher value capacitors need more time to reach a quiescent
DC voltage (usually V
DD/2) when charged with a fixed cur-
rent. The amplifier’s output charges the input capacitor
through the feedback resistor, R
f. Thus, pops can be mini-
mized by selecting an input capacitor value that is no higher
than necessary to meet the desired 3dB frequency.
A shown in
Figure 2, the input resistor (20k
) and the input
capacitor produce a 3dB high pass filter cutoff frequency
that is found using Equation (7).
(7)
As an example when using a speaker with a low frequency
limit of 150Hz, the input coupling capacitor, using Equation
(7), is 0.063F. The 0.33F input coupling capacitor shown
in
Figure 2 allows the LM4835 to drive high efficiency, full
range speaker whose response extends below 30Hz.
OPTIMIZING CLICK AND POP REDUCTION
PERFORMANCE
The LM4835 contains circuitry that minimizes turn-on and
shutdown transients or “clicks and pop”. For this discussion,
turn-on refers to either applying the power supply voltage or
when the shutdown mode is deactivated. While the power
supply is ramping to its final value, the LM4835’s internal
amplifiers are configured as unity gain buffers. An internal
current source changes the voltage of the BYPASS pin in a
controlled, linear manner. Ideally, the input and outputs track
the voltage applied to the BYPASS pin. The gain of the
internal amplifiers remains unity until the voltage on the
bypass pin reaches 1/2 V
DD. As soon as the voltage on the
bypass pin is stable, the device becomes fully operational.
Although the BYPASS pin current cannot be modified,
changing the size of C
B alters the device’s turn-on time and
the magnitude of “clicks and pops”. Increasing the value of
C
B reduces the magnitude of turn-on pops. However, this
presents a tradeoff: as the size of C
B increases, the turn-on
time increases. There is a linear relationship between the
size of C
B and the turn-on time. Here are some typical
turn-on times for various values of C
B:
C
B
T
ON
0.01F
2ms
0.1F
20ms
0.22F
44ms
0.47F
94ms
1.0F
200ms
In order eliminate “clicks and pops”, all capacitors must be
discharged before turn-on. Rapidly switching V
DD may not
allow the capacitors to fully discharge, which may cause
“clicks and pops”. In a single-ended configuration, the output
is coupled to the load by C
OUT. This capacitor usually has a
high value. C
OUT discharges through internal 20k resistors.
Depending on the size of C
OUT, the discharge time constant
can be relatively large. To reduce transients in single-ended
mode, an external 1k
–5k resistor can be placed in par-
allel with the internal 20k
resistor. The tradeoff for using
this resistor is increased quiescent current.
DOCKING STATION INTERFACE
Applications such as notebook computers can take advan-
tage of a docking station to connect to external devices such
as monitors or audio/visual equipment that sends or receives
line level signals. The LM4835 has two outputs, Pin 9 and
Pin 13, which connect to outputs of the internal input ampli-
fiers that drive the volume control inputs. These input ampli-
fiers can drive loads of >1k
(such as powered speakers)
with a rail-to-rail signal. Since the output signal present on
the RIGHT DOCK and LEFT DOCK pins is biased to V
DD/2,
coupling capacitors should be connected in series with the
load. Typical values for the coupling capacitors are 0.33F to
1.0F. If polarized coupling capacitors are used, connect
their ’+’ terminals to the respective output pin.
Since the DOCK outputs precede the internal volume con-
trol, the signal amplitude will be equal to the input signal’s
magnitude and cannot be adjusted. However, the input am-
plifier’s closed-loop gain can be adjusted using external
resistors. These resistors are shown in
Figure 2 as 20k
devices that set each input amplifier’s gain to -1. Use Equa-
tion 8 to determine the input and feedback resistor values for
a desired gain.
-A
v =RF /Ri
(8)
Adjusting the input amplifier’s gain sets the minimum gain for
that channel. The DOCK outputs adds circuit and functional
flexibility because their use supercedes using the inverting
outputs of each bridged output amplifier as line-level out-
puts.
BEEP DETECT FUNCTION
Computers and notebooks produce a system “beep“ signal
that drives a small speaker. The speaker’s auditory output
signifies that the system requires user attention or input. To
accommodate this system alert signal, the LM4835’s pin 11
is a mono input that accepts the beep signal. Internal level
detection circuitry at this input monitors the beep signal’s
magnitude. When a signal level greater than V
DD/2 is de-
tected on pin 11, the bridge output amplifiers are enabled.
The beep signal is amplified and applied to the load con-
DS100139-5
FIGURE 3. Resistor for Varying Output Loads
LM4835
www.national.com
13
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參數(shù)描述 |
|---|---|
| LM4836 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Stereo 2W Audio Power Amplifiers with DC Volume Control, Bass Boost, and Input Mux |
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| LM4836MT | 制造商:OC White Company 功能描述:Audio Amp Headphone/Speaker 2-CH Stereo 2.2W Class-AB 28-Pin TSSOP Rail |
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