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参数资料
| 型号： | LM4700T |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 音频／视频放大 |
| 英文描述： | 30 W, 1 CHANNEL, AUDIO AMPLIFIER, PZFM11 |
| 封装： | TO-220, 11 PIN |
| 文件页数： | 8/19页 |
| 文件大小： | 997K |
| 代理商： | LM4700T |
Application Information
MUTE MODE
By placing a logic-high voltage on the mute pin, the signal
going into the amplifiers will be muted. If the mute pin is left
floating or connected to a logic-low level, the amplifier will be
in a non-muted state. Refer to the Typical Performance
Characteristics section for curves concerning Mute Attenu-
ation vs Mute Pin Voltage.
STANDBY MODE
The standby mode of the LM4700 allows the user to drasti-
cally reduce power consumption when the amplifier is idle.
By placing a logic-high voltage on the standby pin, the
amplifier will go into Standby Mode. In this mode, the current
drawn from the V
CC supply is typically less than 10 A total
for both amplifiers. The current drawn from the V
EE supply is
typically 2.1 mA. Clearly, there is a significant reduction in
idle power consumption when using the standby mode. Re-
fer to the Typical Performance Characteristics section for
curves showing Supply Current vs Standby Pin Voltage for
both supplies.
UNDER-VOLTAGE PROTECTION
Upon system power-up, the under-voltage protection cir-
cuitry allows the power supplies and their corresponding
capacitors to come up close to their full values before turning
on the LM4700 such that no DC output spikes occur. Upon
turn-off, the output of the LM4700 is brought to ground
before the power supplies such that no transients occur at
power-down.
OVER-VOLTAGE PROTECTION
The LM4700 contains over-voltage protection circuitry that
limits the output current to approximately 3.5 Apk while also
providing voltage clamping, though not through internal
clamping diodes. The clamping effect is quite the same,
however, the output transistors are designed to work alter-
nately by sinking large current spikes.
SPiKe PROTECTION
The
LM4700
is
protected
from
instantaneous
peak-
temperature stressing of the power transistor array. The Safe
Operating Area graph in the Typical Performance Charac-
teristics section shows the area of device operation where
SPiKe Protection Circuitry is not enabled. The waveform to
the right of the SOA graph exemplifies how the dynamic
protection will cause waveform distortion when enabled.
THERMAL PROTECTION
The LM4700 has a sophisticated thermal protection scheme
to prevent long-term thermal stress of the device. When the
temperature on the die reaches 165C, the LM4700 shuts
down. It starts operating again when the die temperature
drops to about 155C, but if the temperature again begins to
rise, shutdown will occur again at 165C. Therefore, the
device is allowed to heat up to a relatively high temperature
if the fault condition is temporary, but a sustained fault will
cause the device to cycle in a Schmitt Trigger fashion be-
tween the thermal shutdown temperature limits of 165C and
155C. This greatly reduces the stress imposed on the IC by
thermal cycling, which in turn improves its reliability under
sustained fault conditions.
Since the die temperature is directly dependent upon the
heat sink used, the heat sink should be chosen such that
thermal shutdown will not be reached during normal opera-
tion. Using the best heat sink possible within the cost and
space constraints of the system will improve the long-term
reliability of any power semiconductor device, as discussed
in the Determining the Correct Heat Sink Section.
DETERMINING MAXIMUM POWER DISSIPATION
Power dissipation within the integrated circuit package is a
very important parameter requiring a thorough understand-
ing if optimum power output is to be obtained. An incorrect
maximum power dissipation calculation may result in inad-
equate heat sinking causing thermal shutdown and thus
limiting the output power.
Equation (1) exemplifies the theoretical maximum power
dissipation point of each amplifier where V
CC is the total
supply voltage.
P
DMAX =VCC
2/2
π2R
L
(1)
Thus by knowing the total supply voltage and rated output
load, the maximum power dissipation point can be calcu-
lated. Refer to the graphs of Power Dissipation vs Output
Power in the Typical Performance Characteristics section
which show the actual full range of power dissipation not just
the maximum theoretical point that results from equation (1).
DETERMINING THE CORRECT HEAT SINK
The choice of a heat sink for a high-power audio amplifier is
made entirely to keep the die temperature at a level such
that the thermal protection circuitry does not operate under
normal circumstances.
The thermal resistance from the die (junction) to the outside
air (ambient) is a combination of three thermal resistances,
θ
JC,
θ
CS and
θ
SA. The thermal resistance,
θ
JC (junction to
case), of the LM4700 is 2C/W. Using Thermalloy Therma-
cote thermal compound, the thermal resistance,
θ
CS (case to
sink), is about 0.2C/W. Since convection heat flow (power
dissipation) is analogous to current flow, thermal resistance
is analogous to electrical resistance, and temperature drops
are analogous to voltage drops, the power dissipation out of
the LM4700 is equal to the following:
P
DMAX =(TJMAX TAMB)/
θ
JA
(2)
where T
JMAX = 150C, TAMB is the system ambient tempera-
ture and
θ
JA =
θ
JC +
θ
CS +
θ
SA.
Once the maximum package power dissipation has been
calculated using equation (1), the maximum thermal resis-
tance,
θ
SA, (in C/W) for a heat sink can be calculated. This
calculation is made using equation (3) which is derived by
solving for
θ
SA in equation (2).
θ
SA=[(TJMAXTAMB)PDMAX(
θ
JC+
θ
CS)]/PDMAX (3)
Again it must be noted that the value of
θ
SA is dependent
upon the system designer’s amplifier requirements. If the
ambient temperature that the audio amplifier is to be working
under is higher than 25C, then the thermal resistance for the
heat sink, given all other things are equal, will need to be
smaller.
SUPPLY BYPASSING
The LM4700 has excellent power supply rejection and does
not require a regulated supply. However, to improve system
performance as well as eliminate possible oscillations, the
LM4700 should have its supply leads bypassed with low-
inductance capacitors having short leads that are located
close to the package terminals. Inadequate power supply
bypassing will manifest itself by a low frequency oscillation
known as “motorboating” or by high frequency instabilities.
These instabilities can be eliminated through multiple by-
LM4700
www.national.com
16
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM4700T/NOPB | 制造商:Texas Instruments 功能描述: |
| LM4700TF | 制造商:Texas Instruments 功能描述:IC AMP + MUTE 30W 4700 TO-220-11 |
| LM4700TF | 制造商:Texas Instruments 功能描述:IC AMP + MUTE 30W 4700 TO-220-11 |
| LM4700TF/NOPB | 功能描述:IC AMP AUDIO PWR 30W AB TO220-11 RoHS:是 类别:集成电路 (IC) >> 线性 - 音頻放大器 系列:Overture™ 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:DirectDrive® 类型:H 类 输出类型:耳机，2-通道（立体声） 在某负载时最大输出功率 x 通道数量:35mW x 2 @ 16 欧姆 电源电压:1.62 V ~ 1.98 V 特点:I²C，麦克风，静音，短路保护，音量控制 安装类型:表面贴装 供应商设备封装:25-WLP（2.09x2.09） 封装/外壳:25-WFBGA，WLCSP 包装:带卷 (TR) |
| LM4701 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:LM4701 Overture⑩ Audio Power Amplifier Series 30W Audio Power Amplifier with Mute and Standby Modes |
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