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參數(shù)資料
| 型號(hào)： | LM4961LQ |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 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)： | 8/16頁(yè) |
| 文件大?。?/td> | 509K |
| 代理商： | LM4961LQ |
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Application Information
BRIDGE CONFIGURATION EXPLANATION
The Audio Amplifier portion of the LM4961 has two internal
amplifiers allowing different amplifier configurations. The first
amplifier’s gain is externally configurable, whereas the sec-
ond amplifier is internally fixed in a unity-gain, inverting
configuration. The closed-loop gain of the first amplifier is set
by selecting the ratio of Rf to Ri while the second amplifier’s
gain is fixed by the two internal 20k
resistors. Figure 1
shows that the output of amplifier one serves as the input to
amplifier two. This results in both amplifiers producing sig-
nals identical in magnitude, but out of phase by 180. Con-
sequently, the differential gain for the Audio Amplifier is
A
VD
= 2 *(Rf/Ri)
By driving the load differentially through outputs Vo1 and
Vo2, an amplifier configuration commonly referred to as
“bridged mode” is established. Bridged mode operation is
different from the classic single-ended amplifier configura-
tion where one side of the load is connected to ground.
A bridge amplifier design has a few distinct advantages over
the single-ended configuration. It provides differential drive
to the load, thus doubling the output swing for a specified
supply voltage. Four times the output power is possible as
compared to a single-ended amplifier under the same con-
ditions.
The bridge configuration also creates a second advantage
over single-ended amplifiers. Since the differential outputs,
Vo1 and Vo2, are biased at half-supply, no net DC voltage
exists across the load. This eliminates the need for an output
coupling capacitor which is required in a single supply,
single-ended amplifier configuration. Without an output cou-
pling capacitor, the half-supply bias across the load would
result in both increased internal IC power dissipation and
also possible loudspeaker damage.
AMPLIFIER POWER DISSIPATION
Power dissipation is a major concern when designing a
successful amplifier, whether the amplifier is bridged or
single-ended. A direct consequence of the increased power
delivered to the load by a bridge amplifier is an increase in
internal power dissipation. Since the amplifier portion of the
LM4961 has two operational amplifiers, the maximum inter-
nal power dissipation is 4 times that of a single-ended am-
plifier. The maximum power dissipation for a given BTL
application can be derived from Equation 1.
P
DMAX(AMP)
= 4(V
DD
)
2
/ (2
π
2
Z
L
)
(1)
where
Z
L
= R
o
1 + R
o
2 +1/2
π
fc
BOOST CONVERTER POWER DISSIPATION
At higher duty cycles, the increased ON-time of the switch
FET means the maximum output current will be determined
by power dissipation within the LM4961 FET switch. The
switch power dissipation from ON-time conduction is calcu-
lated by Equation 2.
P
DMAX(SWITCH)
= DC x I
IND
(AVE)
2
x R
DS
(ON)
(2)
where DC is the duty cycle.
There will be some switching losses as well, so some derat-
ing needs to be applied when calculating IC power dissipa-
tion.
TOTAL POWER DISSIPATION
The total power dissipation for the LM4961 can be calculated
by adding Equation 1 and Equation 2 together to establish
Equation 3:
P
DMAX(TOTAL)
= [4*(V
DD
)
2
/
2
π
2
Z
L
]+[DCxI
IND
(AVE)
2
xR
DS
(ON)]
(3)
The result from Equation 3 must not be greater than the
power dissipation that results from Equation 4:
P
DMAX
= (T
JMAX
- T
A
) /
θ
JA
(4)
For the LQA28A,
θ
= 66C/W. T
= 125C for the
LM4961. Depending on the ambient temperature, T
, of the
system surroundings, Equation 4 can be used to find the
maximum internal power dissipation supported by the IC
packaging. If the result of Equation 3 is greater than that of
Equation 4, then either the supply voltage must be in-
creased, the load impedance increased or T
reduced. For
the typical application of a 4.2V power supply, with a
2uF+30
load, the maximum ambient temperature possible
without violating the maximum junction temperature is ap-
proximately 109C provided that device operation is around
the maximum power dissipation point. Thus, for typical ap-
plications, power dissipation is not an issue. Power dissipa-
tion is a function of output power and thus, if typical opera-
tion is not around the maximum power dissipation point, the
ambient temperature may be increased accordingly. Refer to
the Typical Performance Characteristics curves for power
dissipation information for lower output levels.
EXPOSED-DAP PACKAGE PCB MOUNTING
CONSIDERATIONS
The LM4961’s exposed-DAP (die attach paddle) package
(LD) provides a low thermal resistance between the die and
the PCB to which the part is mounted and soldered. The low
thermal resistance allows rapid heat transfer from the die to
the surrounding PCB copper traces, ground plane, and sur-
rounding air. The LD package should have its DAP soldered
to a copper pad on the PCB. The DAP’s PCB copper pad
may be connected to a large plane of continuous unbroken
copper. This plane forms a thermal mass, heat sink, and
radiation area. Further detailed and specific information con-
cerning PCB layout, fabrication, and mounting an LD (LLP)
package is found in National Semiconductor’s Package En-
gineering Group under application note AN1187.
SHUTDOWN FUNCTION
In many applications, a microcontroller or microprocessor
output is used to control the shutdown circuitry to provide a
quick, smooth transition into shutdown.Another solution is to
use a single-pole, single-throw switch connected between
V
DD
and Shutdown pins.
BAND SWITCH FUNCTION
The LM4961 features a Band Switch function which allows
the user to use one amplifier for both receiver (earpiece)
mode and ringer/loudspeaker mode. When a logic high
L
www.national.com
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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 開發(fā)工具 LM4961LQ EVAL BOARD RoHS:否 制造商:Texas Instruments 產(chǎn)品:Evaluation Kits 類型: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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