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參數(shù)資料
| 型號： | LM4755MWC |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 11 W, 2 CHANNEL, AUDIO AMPLIFIER, UUC |
| 封裝： | WAFER |
| 文件頁數(shù)： | 3/19頁 |
| 文件大小： | 756K |
| 代理商： | LM4755MWC |
Application Information (Continued)
threshold voltage is desired. One example is a design requir-
ing a high operating supply voltage, with large supply and
bias capacitors, and there is little or no other circuitry con-
nected to the main power supply rail. In this circuit, when the
power is disconnected, the supply and bias capacitors will
discharge at a slower rate, possibly resulting in audible
output distortion as the decaying voltage begins to clip the
output signal. An external circuit may be used to sense for
the desired threshold, and pull the bias line (pin 6) to ground
to disable the input preamp.
Figure 6 shows an example of
such a circuit. When the voltage across the zener diode
drops below its threshold, current flow into the base of Q1 is
interrupted. Q2 then turns on, discharging the bias capacitor.
This discharge rate is governed by several factors, including
the bias capacitor value, the bias voltage, and the resistor at
the emitter of Q2. An equation for approximating the value of
the emitter discharge resistor, R, is given below:
R = (0.7v) / (Cb
(V
CC/2) / 0.1s)
Note that this is only a linearized approximation based on a
discharge time of 0.1s. The circuit should be evaluated and
adjusted for each application.
As mentioned earlier in the Built-in Mute Circuit section,
when using an external circuit to pull down the bias line, the
rate of discharge will have an effect on the turn-off induced
distortions. Please refer to the Built-in Mute Circuit section
for more information.
THERMAL CONSIDERATIONS
Heat Sinking
Proper heatsinking is necessary to ensure that the amplifier
will function correctly under all operating conditions. A heat-
sink that is too small will cause the die to heat excessively
and will result in a degraded output signal as the thermal
protection circuitry begins to operate.
The choice of a heatsink for a given application is dictated by
several factors: the maximum power the IC needs to dissi-
pate, the worst-case ambient temperature of the circuit, the
junction-to-case thermal resistance, and the maximum junc-
tion temperature of the IC. The heat flow approximation
equation used in determining the correct heatsink maximum
thermal resistance is given below:
T
J–TA =PDMAX (θJC + θCS + θSA)
where:
P
DMAX = maximum power dissipation of the IC
T
J(C) = junction temperature of the IC
T
A(C) = ambient temperature
θ
JC(C/W) = junction-to-case thermal resistance of the IC
θ
CS(C/W) = case-to-heatsink thermal resistance (typically
0.2 to 0.5 C/W)
θ
SA(C/W) = thermal resistance of heatsink
When determining the proper heatsink, the above equation
should be re-written as:
θ
SA ≤ [(TJ–TA)/PDMAX]- θJC–θCS
TO-263 HEATSINKING
Surface mount applications will be limited by the thermal
dissipation properties of printed circuit board area. The
TO-263 package is not recommended for surface mount
applications with V
S > 16V due to limited printed circuit
board area. There are TO-263 package enhancements,
such as clip-on heatsinks and heatsinks with adhesives, that
can be used to improve performance.
Standard FR-4 single-sided copper clad will have an ap-
proximate Thermal resistance (
θ
SA) ranging from:
1.5 x 1.5 in. sq.
20–27C/W
(T
A=28C, Sine wave
testing, 1 oz. Copper)
2 x 2 in. sq.
16–23C/W
The above values for
θ
SA vary widely due to dimensional
proportions (i.e. variations in width and length will vary
θ
SA).
For audio applications, where peak power levels are short in
duration, this part will perform satisfactory with less
heatsinking/copper clad area. As with any high power design
proper bench testing should be undertaken to assure the
design can dissipate the required power. Proper bench test-
ing requires attention to worst case ambient temperature
and air flow. At high power dissipation levels the part will
show a tendency to increase saturation voltages, thus limit-
ing the undistorted power levels.
DETERMINING MAXIMUM POWER DISSIPATION
For a single-ended class AB power amplifier, the theoretical
maximum power dissipation point is a function of the supply
voltage, V
S, and the load resistance, RL and is given by the
following equation:
(single channel)
P
DMAX (W)=[VS
2 /(2
π2 R
L)]
The above equation is for a single channel class-AB power
amplifier. For dual amplifiers such as the LM4755, the equa-
tion for calculating the total maximum power dissipated is:
(dual channel)
P
DMAX (W)=2 [VS
2 /(2
π2 R
L)]
or
V
S
2 /(
π2 R
L)
(Bridged Outputs)
P
DMAX (W) = 4[VS
2 /(2
π2 R
L)]
HEATSINK DESIGN EXAMPLE:
Determine the system parameters:
V
S = 24V
Operating Supply Voltage
R
L =4
Minimum Load Impedance
T
A = 55C
Worst Case Ambient Temperature
Device parameters from the datasheet:
T
J = 150C
Maximum Junction Temperature
DS100059-32
FIGURE 6. External Undervoltage Pull-Down
LM4755
www.national.com
11
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4755T | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Stereo 11W Audio Power Amplifier with Mute |
| LM4755T/NOPB | 功能描述:IC AMP AUDIO PWR 11W AB TO220-9 RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:- 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:2,500 系列:DirectDrive® 類型:H 類 輸出類型:耳機，2-通道（立體聲） 在某負(fù)載時最大輸出功率 x 通道數(shù)量:35mW x 2 @ 16 歐姆 電源電壓:1.62 V ~ 1.98 V 特點:I²C，麥克風(fēng)，靜音，短路保護(hù)，音量控制 安裝類型:表面貼裝 供應(yīng)商設(shè)備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
| LM4755T/NOPB | 制造商:Texas Instruments 功能描述:Audio Power Amplifier IC |
| LM4755TS | 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 |
| LM4755TS/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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