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參數(shù)資料
| 型號： | LM4752T/NOPB |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 7 W, 2 CHANNEL, AUDIO AMPLIFIER, PZFM7 |
| 封裝： | LEAD FREE, PLASTIC, TO-220, 7 PIN |
| 文件頁數(shù)： | 8/22頁 |
| 文件大?。?/td> | 521K |
| 代理商： | LM4752T/NOPB |
external circuit may be used to sense for the desired thresh-
old, and pull the bias line (pin5) to ground to disable the input
preamp. Figure 7 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 gov-
erned 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) / (C
B (V S / 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 Application Circuit with Mute
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 Application Circuit
with Mute
section for more information.
10003932
FIGURE 7. External Undervoltage Pull-Down
THERMAL CONSIDERATIONS
Heat Sinking
Proper heatsinking is necessary to ensure that the amplifier
will function correctly under all operating conditions. A
heatsink that is too small will cause the die to heat excessively
and will result in a degraded output signal as the internal ther-
mal 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 equa-
tion used in determining the correct heatsink maximum
thermal resistance is given below:
T
J–TA = P DMAX (θJC + θCS + θ SA)
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] θ JC θCS
TO-263 Heatsinking
Surface mount applications will be limited by the thermal dis-
sipation 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 approx-
imate Thermal resistance (
θ
SA) ranging from:
1.5 × 1.5 in. sq.
20–27°C/W
(T
A=28°C, Sine wave
testing, 1 oz. Copper)
2 × 2 in. sq.
16–23°C/W
The above values for
θ
SA vary widely due to dimensional pro-
portions (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 heatsink-
ing/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 testing 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 limiting 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 LM4752, the equa-
tion for calculating the total maximum power dissipated is:
(dual channel)
P
DMAX (W) = 2 [V S
2
/ (2
π2 R
L) ]
or
V
S
2
/ (
π 2 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 = 55°C
Worst case ambient temperature
Device parameters from the datasheet:
T
J = 150°C
Maximum junction temperature
θ
JC = 2°C/W
Junction-to-case thermal resistance
Calculations:
www.national.com
16
LM4752
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM4752TS | 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: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM4752TS/NOPB | 功能描述:音頻放大器 STEREO 11W AUDIO PWR AMP 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: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM4753 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Dual 10W Audio Power Amplifier w/Mute, Standby and Volume Control |
| LM4753T | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| LM4755 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Stereo 11W Audio Power Amplifier with Mute |
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