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參數(shù)資料
| 型號(hào)： | 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)： | 15/20頁 |
| 文件大小： | 586K |
| 代理商： | LM4652 |
Application Information
(Continued)
C
1
should be in the range of 0.1μF to 1μF or 2 - 20% of C
BYP
.
R
fl1
and R
fl2
are found by the ratio R
fl1
= 10R
fl2
.
Alower ratio can be used if the application is for lower output
voltages than the 125Watt, 4
solution show here.
The feedback RC filter’s pole location should be higher than
the output filter pole. The reason for two capacitors in paral-
lel instead of one larger capacitor is to reduce the possible
EMI from the feedback traces. C
is placed close as pos-
sible to the output of the LM4652 so that an audio signal is
present on the feedback trace instead of a high frequency
square wave. C
is then placed as close as possible to the
feedback inputs (pins 14, 19) of the LM4651 to filter off any
noise picked up by the feedback traces. The combination
lowers EMI and provides a cleaner audio feedback signal to
the LM4651. R
should be in range of 100k
to1M
. C
f
controls the bandwidth of the error signal and should be in
the range of 100pF to 470pF.
Determine the Value for C
START
(Start Up Delay)
The start-up delay is chosen to be 1 second to ensure
minimum pops or clicks when the amplifier is powered up.
Using Equation (2), the value of C
START
is 11.7μF.Astandard
value of 10μF is used.
Determine the Value of Gain, R
1
, and R
2
The gain is set to produce a 125W output at no more than
1% distortion with a 3V
input. A dissipation of 125W in a
4
load requires a 22.4V
signal. To produce this output
signal, the LM4651/LM4652 amplifier needs an overall
closed-loop gain of 22.4V
/3V
, or 7.5V/V (17.5db).
Equation (12) shows all the variables that affect the system
gain.
Gain = [(R
2
/ R
1
) x ((R
fl1
+ R
fl2
)/ R
fl2
) (R
2
/ R
1
) + .5].(3)
The values for R
, R
, and R
were found in the
Determine
the Value of the Filters
section above. Therefore, R
fI1
=
620k
, R
= 62k
and R
= 390k
. The value of V
CC
was
also found as the first step in this example to be
±
20V.
Inserting these values into equation (12) and reducing gives
the equation below:
R
2
= .7R
1
(4)
The input resistance is desired to be 20k
so R
1
is set to
20k
. R
2
is then found to be 14k
.
Lowering R
direcly affects the noise of the system. Chang-
ing R
to increase gain with the lower value for R
has very
little affect on the noise level. The percent change in noise is
about what whould be expected with a higher gain. The
drawback to a lower R
value is a larger C
value, neces-
sary to properly couple the lowest desired signal frequen-
cies. If a 20k
input impedance is not required, then the
recommended values shown in Figure 1
Typical Audio
Application Circuit
should be used: with R
’s value set to
4.7k
and R
2
’s value set to 3.5k
for a gain 7.5V/V.
Determine the Needed Heat Sink
The only remaining design requirement is a thermal design
that prevents activating the thermal protection circuitry. Use
Equations (9) - (11) to calculate the amount of power dissi-
pation for the LM4652. The appropriate heat sink size, or
thermal resistance in C/W, will then be determined.
Equation (9) determines the percentage of loss caused by
the switching. Use the typical values given in the
Electrical
Characteristics for the LM4651
and
Electrical Character-
istics for the LM4652
tables for the rise time, fall time and
over modulation time:
%Loss = (25ns+26ns+350ns)
*
125kHz
%Loss = 5.0%
This switching loss causes a maximum power dissipation,
using Equation (10), of:
P
DSWITCH
= (5.0%
*
125W) / (15.0%)
P
DSWITCH
= 6.6W
Next the power dissipation caused by the R
of the
output FETs is found by multiplying the output current times
the R
. Again, the value for R
is found from the
Electrical Characteristics for the LM4652
table above.
The value for R
at 100C is used since we are calcu-
lating the maximum power dissipation.
I
OUTRMS
= SQRT(125watts/4
) = 5.59 amps
P
RDS(ON)
= (5.59A)
2
*
(0.230
*
2)
P
RDS(ON)
= 14.4W
The total power dissipation in the LM4652 is the sum of
these two power losses giving:
P
DTOTAL
= 6.6W + 14.4W = 21W
The value for Maximum Power Dissipation given in the
Sys-
tem Electrical Characteristics for the LM4651 and
LM4652
is 22 watts. The difference is due to approximately
1 watt of power loss in the LM4651. The above calculations
are for the power loss in the LM4652.
Lastly, use Equation (11) to determine the thermal resistance
of the LM4652’s heat sink. The values for
θ
JC
and T
JMAX
are
found in the
Operating Ratings
and the
mum Ratings
section above for the LM4652. The value of
θ
is 2C/W for the isolated (TF) package or 1C/W for the
non-isolated (T) package. The value for T
is 150C. The
value for
θ
is set to 0.2C/W since this is a reasonable
value when thermal grease is used. The maximum ambient
temperature from the design requirements is 50. The value
of
θ
SA
for the isolated (TF) package is:
θ
SA
= [(150C 50C)/21W] 2C/W 0.2C/W
θ
SA
= 2.5C/W
and for the non-isolated (T) package without a mica washer
to isolate the heat sink from the package:
θ
SA
= [(150C 50C)/21W] 1C/W 0.2C/W
θ
SA
= 3.5C/W
L
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相關(guān)代理商/技術(shù)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(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(jī)，2-通道（立體聲） 在某負(fù)載時(shí)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(diǎn):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) |
| 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(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(jī)，2-通道（立體聲） 在某負(fù)載時(shí)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(diǎn):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) |
| LM4652TF | 制造商:Texas Instruments 功能描述:IC QUAD PWRFET CLASS D 170W 4652 |
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