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參數(shù)資料
| 型號： | LM4652 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | LM4651 & LM4652 Overture⑩ Audio Power Amplifier 170W Class D Audio Power Amplifier Solution |
| 中文描述： | LM4651 |
| 文件頁數(shù)： | 14/20頁 |
| 文件大?。?/td> | 586K |
| 代理商： | LM4652 |
Application Information
(Continued)
LM4652 is the R
of the FET times the RMS output
current when operating at maximum output power. The other
component of power dissipation in the LM4652 is the switch-
ing loss. If the output power is high enough and the DC
resistance of the filter coils is not minimized then significant
loss can occur in the output filter. This will not affect the
power dissipation in the LM4652 but should be checked to
be sure that the filter coils with not over heat.
The first step in determining the maximum power dissipation
is finding the maximum output power with a given voltage
and load. Refer to the graph
Output Power verses Supply
Voltage
to determine the output power for the given load and
supply voltage. From this power, the RMS output current can
be calculated as I
= SQRT(P
/R
). The power
dissipation caused by the output current is P
DOUT
=
(I
)
2
*
(2 * R
). The value for R
found from the
Electrical Characteristics for the LM4652
table above. The percentage of loss due to the switching is
calculated by Equation (9):
%LOSS
SWITCH
= (t
r
+ t
f
+ T
OVERMOD
)
*
f
SW
(9)
t
r
, t
f
and T
OVERMOD
can be found in the
Electrical Charac-
teristic for the LM4651
and
Electrical Characteristic for
the LM4652
sections above. The system designer deter-
mines the value for f
(switching frequency). Power dissi-
pation caused by switching loss is found by Equation (10).
P
is the 1% output power for the given supply voltage
and the load impedance being used in the application. P
OUT-
MAX
can be determined from the graph
Output Power vs.
Supply Voltage
in the
Typical Performance Characteris-
tics
section above.
P
DSWITCH
= (%LOSS
SWITCH
*
P
OUTMAX
) /
(1%LOSS
SWITCH
)
(Watts)
(10)
P
for the LM4652 is found by adding the two compo-
nents (P
DSWITCH
+ P
DOUT
) of power dissipation together.
Determining the Correct Heat Sink
Once the LM4652’s power dissipation known, the maximum
thermal resistance (in C/W) of a heat sink can be calculated.
This calculation is made using Equation (11) and is based on
the fact that thermal heat flow parameters are analogous to
electrical current flow properties.
P
DMAX
= (T
JMAX
T
AMBIENTMAX
) /
θ
JA
Where
θ
JA
=
θ
JC
+
θ
CS
+
θ
SA
(Watts)
(11)
Since we know
θ
JC
,
θ
CS
, and T
JMAX
from the
Absolute
Maximum Ratings
and
sections above
(taking care to use the correct
θ
for the LM4652 depending
on which package type is being used in the application) and
have calculated P
and T
, we only need
θ
,
the heat sink’s thermal resistance. The following equation is
derived from Equation (11):
θ
SA
= [(T
JMAX
T
AMBIENTMAX
) / P
DMAX
]
θ
JC
θ
CS
Again, it must be noted that the value of
θ
is dependent
upon the system designer’s application and its correspond-
ing parameters as described previously. If the ambient tem-
perature surrounding the audio amplifier is higher than
T
AMBIENTMAX
, then the thermal resistance for the heat sink,
given all other parameters are equal, will need to be lower.
Example Design of a Class D Amplifier
The following is an example of how to design a class D
amplifier system for a power subwoofer application utilizing
the LM4651 and LM4652 to meet the design requirements
listed below:
Output Power, 1% THD
Load Impedance
Input Signal level
Input Signal Bandwidth
Ambient Temperature
125W
4
3V RMS (max)
10Hz 150Hz
50C (max)
Determine the Supply Voltage
From the graph
Output Power verses Supply voltage at
1% THD
the supply voltage needed for a 125 watt, 4
application is found to be
±
20V.
Determine the Value for R
OSC
(Modulation Frequency)
The oscillation frequency is chosen to obtain a satisfactory
efficiency level while also maintaining a reasonable THD
performance. The modulation frequency can be chosen us-
ing the
Clipping Power Point and Efficiency verses
Switching Frequency
graph. A modulation frequency of
125kHz is found to be a good middle ground for THD per-
formance and efficiency. The value of the resistor for R
OSC
is
found from Equation (6) to be 3.9 k
.
Determine the Value for R
SCKT
(Circuit Limit)
The current limit is internally set as a failsafe to 10 amps.
The inductor ripple current and the peak output current must
be lower than 10 amps or current limit protection will turn on.
Atypical 4
load driven by a filter using 50μH inductors does
not require more than 10A. The current limit will have to be
increased when loads less than 4
are used to acheive
higher output power. With R
SCKT
equal to 100k
, the current
limit is 10A.
Determine the Value for R
DLY
(Dead Time Control)
The delay time or dead time is set to the recommended
value so R
equals 5k
. If a higher bandwidth of operation
is desired, R
DLY
should be a lower value resistor. If a zero
value for R
DLY
is desired, connect the LM4651’s pin 17 to
GND.
Determine the Value of L
1
, C
BYP
, C
1
, R
fl1
R
fl2
, C
fl1
C
fl2
, R
f
,
C
f
(the Output and Feedback Filters)
All component values show in Figure 1
Typical Audio Ap-
plication Circuit
, are optimized for a subwoofer application.
Use the following guidelines when changing any component
values from those shown. The frequency response of the
output filter is controlled by L
and C
. Refer to the
Ap-
plication Information
section titled
Output Stage Filtering
for a detailed explanation on calculating the correct values
for L
1
and C
BYP
.
L
www.national.com
14
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM4652TA | 制造商:Texas Instruments 功能描述:IC QUAD PWRFET CLASS D 170W 4652 |
| LM4652TA | 制造商:Texas Instruments 功能描述:IC QUAD PWRFET CLASS D 170W 4652 |
| LM4652TA/NOPB | 功能描述:IC AMP AUDIO PWR 170W D TO220-15 RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Overture™ 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝: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，靜音，短路保護，音量控制 安裝類型:表面貼裝 供應商設備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
| LM4652TF | 功能描述:IC AMP AUDIO PWR 170W D TO220-15 RoHS:否 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Overture™ 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝: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，靜音，短路保護，音量控制 安裝類型:表面貼裝 供應商設備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
| LM4652TF | 制造商:Texas Instruments 功能描述:IC QUAD PWRFET CLASS D 170W 4652 |
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