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參數(shù)資料
| 型號(hào)： | LM4961LQ |
| 廠(chǎng)商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類(lèi)： | 音頻／視頻放大 |
| 英文描述： | Ceramic Speaker Driver |
| 中文描述： | 1 CHANNEL, AUDIO AMPLIFIER, QCC28 |
| 封裝： | 5 X 5 MM, LLP-28 |
| 文件頁(yè)數(shù)： | 10/16頁(yè) |
| 文件大小： | 509K |
| 代理商： | LM4961LQ |
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Application Information
(Continued)
and Y5F have such severe loss of capacitance due to effects
of temperature variation and applied voltage, they may pro-
vide as little as 20% of rated capacitance in many typical
applications. Always consult capacitor manufacturer’s data
curves before selecting a capacitor. High-quality ceramic
capacitors can be obtained from Taiyo-Yuden.
POWER SUPPLY BYPASSING
As with any amplifier, proper supply bypassing is critical for
low noise performance and high power supply rejection. The
capacitor location on both V1 and V
DD
pins should be as
close to the device as possible.
SELECTING INPUT CAPACITOR FOR AUDIO
AMPLIFIER
One of the major considerations is the closedloop bandwidth
of the amplifier. To a large extent, the bandwidth is dictated
by the choice of external components shown in Figure 1. The
input coupling capacitor, C
, forms a first order high pass filter
which limits low frequency response. This value should be
chosen based on needed frequency response for a few
distinct reasons.
High value input capacitors are both expensive and space
hungry in portable designs. Clearly, a certain value capacitor
is needed to couple in low frequencies without severe at-
tenuation. But ceramic speakers used in portable systems,
whether internal or external, have little ability to reproduce
signals below 100Hz to 150Hz. Thus, using a high value
input capacitor may not increase actual system perfor-
mance.
In addition to system cost and size, click and pop perfor-
mance is affected by the value of the input coupling capaci-
tor, C
. A high value input coupling capacitor requires more
charge to reach its quiescent DC voltage (nominally 1/2
V
). This charge comes from the output via the feedback
and is apt to create pops upon device enable. Thus, by
minimizing the capacitor value based on desired low fre-
quency response, turn-on pops can be minimized.
SELECTING BYPASS CAPACITOR FOR AUDIO
AMPLIFIER
Besides minimizing the input capacitor value, careful consid-
eration should be paid to the bypass capacitor value. Bypass
capacitor, C
, is the most critical component to minimize
turn-on pops since it determines how fast the amplifer turns
on. The slower the amplifier’s outputs ramp to their quies-
cent DC voltage (nominally 1/2 V
), the smaller the turn-on
pop. Choosing C
equal to 1.0μF along with a small value of
C
(in the range of 0.039μF to 0.39μF), should produce a
virtually clickless and popless shutdown function. Although
the device will function properly, (no oscillations or motor-
boating), with C
B
equal to 0.1μF, the device will be much
more susceptible to turn-on clicks and pops. Thus, a value of
C
B
equal to 1.0μF is recommended in all but the most cost
sensitive designs.
SELECTING FEEDBACK CAPACITOR FOR AUDIO
AMPLIFIER
The LM4961 is unity-gain stable which gives the designer
maximum system flexability. However, to drive ceramic
speakers, a typical application requires a closed-loop differ-
ential gain of 10. In this case a feedback capacitor (C
2) will
be needed as shown in Figure 1 to bandwidth limit the
amplifier.
This feedback capacitor creates a low pass filter that elimi-
nates possible high frequency noise. Care should be taken
when calculating the -3dB frequency because an incorrect
combination of R
f
and C
f
2 will cause rolloff before the de-
sired frequency
SELECTING OUTPUT CAPACITOR (C
O
) FOR BOOST
CONVERTER
A single 4.7μF to 10μF ceramic capacitor will provide suffi-
cient output capacitance for most applications. If larger
amounts of capacitance are desired for improved line sup-
port and transient response, tantalum capacitors can be
used. Aluminum electrolytics with ultra low ESR such as
Sanyo Oscon can be used, but are usually prohibitively
expensive. Typical AI electrolytic capacitors are not suitable
for switching frequencies above 500 kHz because of signifi-
cant ringing and temperature rise due to self-heating from
ripple current. An output capacitor with excessive ESR can
also reduce phase margin and cause instability.
In general, if electrolytics are used, we recommended that
they be paralleled with ceramic capacitors to reduce ringing,
switching losses, and output voltage ripple.
SELECTING INPUT CAPACITOR (Cs1) FOR BOOST
CONVERTER
An input capacitor is required to serve as an energy reservoir
for the current which must flow into the coil each time the
switch turns ON. This capacitor must have extremely low
ESR, so ceramic is the best choice. We recommend a
nominal value of 4.7μF, but larger values can be used. Since
this capacitor reduces the amount of voltage ripple seen at
the input pin, it also reduces the amount of EMI passed back
along that line to other circuitry.
SETTING THE OUTPUT VOLTAGE (V
1
) OF BOOST
CONVERTER
The output voltage is set using the external resistors R1 and
R2 (see Figure 1). A value of approximately 13.3k
is rec-
ommended for R2 to establish a divider current of approxi-
mately 92μA. R1 is calculated using the formula:
R1 = R2 X (V
2
/1.23 1)
(5)
FEED-FORWARD COMPENSATION FOR BOOST
CONVERTER
Although the LM4961’s internal Boost converter is internally
compensated, the external feed-forward capacitor C
is re-
quired for stability (see Figure 1). Adding this capacitor puts
a zero in the loop response of the converter. The recom-
mended frequency for the zero fz should be approximately
6kHz. C
f
1 can be calculated using the formula:
C
f
1 = 1 / (2 X R1 X fz)
(6)
SELECTING DIODES
The external diode used in Figure 1 should be a Schottky
diode. A 20V diode such as the MBR0520 from Fairchild
Semiconductor is recommended.
The MBR05XX series of diodes are designed to handle a
maximum average current of 0.5A. For applications exceed-
ing 0.5A average but less than 1A, a Microsemi UPS5817
can be used.
L
www.national.com
10
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4961LQ/NOPB | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產(chǎn)品:General Purpose Audio Amplifiers 輸出類(lèi)型:Digital 輸出功率: THD + 噪聲: 工作電源電壓:3.3 V 電源電流: 最大功率耗散: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM4961LQBD | 功能描述:音頻 IC 開(kāi)發(fā)工具 LM4961LQ EVAL BOARD RoHS:否 制造商:Texas Instruments 產(chǎn)品:Evaluation Kits 類(lèi)型:Audio Amplifiers 工具用于評(píng)估:TAS5614L 工作電源電壓:12 V to 38 V |
| LM4961LQBD/NOPB | 制造商:Texas Instruments 功能描述:Evaluation Kit For Ceramic Speaker Driver |
| LM4961LQX | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產(chǎn)品:General Purpose Audio Amplifiers 輸出類(lèi)型:Digital 輸出功率: THD + 噪聲: 工作電源電壓:3.3 V 電源電流: 最大功率耗散: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM4961LQX/NOPB | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產(chǎn)品:General Purpose Audio Amplifiers 輸出類(lèi)型:Digital 輸出功率: THD + 噪聲: 工作電源電壓:3.3 V 電源電流: 最大功率耗散: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
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