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参数资料
| 型号： | LM4913MH/NOPB |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 音频／视频放大 |
| 英文描述： | 0.09 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO10 |
| 封装： | TSSOP-10 |
| 文件页数： | 5/18页 |
| 文件大小： | 1078K |
| 代理商： | LM4913MH/NOPB |
200617a2
FIGURE 4. Headphone Circuit
SELECTING EXTERNAL COMPONENTS
Input Capacitor Value Selection
Amplifying the lowest audio frequencies requires high value
input coupling capacitor (C
i in Figure 2). A high value capac-
itor can be expensive and may compromise space efficiency
in portable designs. In many cases, however, the speakers
used in portable systems, whether internal or external, have
little ability to reproduce signals below 150Hz. Applications
using speakers with this limited frequency response reap little
improvement by using large input capacitor.
The LM4913's advanced output transient suppression circuit-
ry has eliminated the need to select the input capacitor's value
in relation to the BYPASS capacitor's value as was necessary
in some previous Boomer amplifiers. The value of C
i is now
strictly determined by the desired low frequency response.
As shown in Figure 2, the input resistor (Ri) and the input ca-
pacitor (C
i) produce a high pass filter cutoff frequency that is
found using Equation (7).
f
C = 1 / 2πRiCi
(7)
As an example when using a speaker with a low frequency
limit of 150Hz, C
i, using Equation (7) is 0.063F. The 1.0F
C
i shown in Figure 2 allows the LM4913 to drive high effi-
ciency, full range speaker whose response extends below
30Hz.
Bypass Capacitor Value Selection
Besides minimizing the input capacitor size, careful consid-
eration should be paid to value of C
B, the capacitor connected
to the BYPASS pin. Since C
B determines how fast the
LM4913 settles to quiescent operation, its value is critical
when minimizing turn-on pops. The slower the LM4913's out-
puts ramp to their quiescent DC voltage (nominally V
DD/2),
the smaller the turn-on pop. Choosing C
B equal to 1.0F along
with a small value of C
i (in the range of 0.1F to 0.39F), pro-
duces a click-less and pop-less shutdown function. As dis-
cussed above, choosing C
i no larger than necessary for the
desired bandwidth helps minimize clicks and pops. C
B's value
should be in the range of 5 times to 7 times the value of C
i.
This ensures that output transients are eliminated when pow-
er is first applied or the LM4913 resumes operation after
shutdown.
OPTIMIZING CLICK AND POP REDUCTION
PERFORMANCE
The LM4913 contains circuitry that eliminates turn-on and
shutdown transients ("clicks and pops") and transients that
could occur when switching between BTL speakers and sin-
gle-ended headphones. For this discussion, turn-on refers to
either applying the power supply voltage or when the micro-
power shutdown mode is deactivated.
As the V
DD/2 voltage present at the BYPASS pin ramps to its
final value, the LM4913's internal amplifiers are configured as
unity gain buffers and are disconnected from the RO/MO+
and LO/MO- pins. An internal current source charges the ca-
pacitor connected between the BYPASS pin and GND in a
controlled, linear manner. Ideally, the input and outputs track
the voltage applied to the BYPASS pin. The gain of the inter-
nal amplifiers remains unity until the voltage on the bypass
pin reaches V
DD/2. As soon as the voltage on the bypass pin
is stable, the device becomes fully operational and the am-
plifier outputs are reconnected to their respective output pins.
Although the BYPASS pin current cannot be modified, chang-
ing the size of C
B alters the device's turn-on time. 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(F)
T
ON (ms)
0.01
2
0.1
20
0.22
42
0.47
90
1.0
200
2.2
420
In order eliminate "clicks and pops", all capacitors must be
discharged before turn-on. Rapidly switching V
DD may not al-
low the capacitors to fully discharge, which may cause "clicks
and pops".
13
www.national.com
LM4913
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM4913MHX/NOPB | 制造商:Texas Instruments 功能描述:Audio Amp Headphone/Speaker 1-CH Mono/2-CH Stereo 2W Class-AB 10-Pin TSSOP EP T/R |
| LM4913MM | 制造商:NSC 制造商全称:National Semiconductor 功能描述:2W Monaural, 90mW Stereo Headphone Audio Amplifier |
| LM4914 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:1W Monaural, 85mW Stereo Headphone Audio Amplifier |
| LM4914A WAF | 制造商:Texas Instruments 功能描述: |
| LM4914MH | 制造商:NSC 制造商全称:National Semiconductor 功能描述:1W Monaural, 85mW Stereo Headphone Audio Amplifier |
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