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參數(shù)資料
| 型號(hào)： | LM4879IBP |
| 元件分類： | 音頻放大器 |
| 英文描述： | AUDIO AMPLIFIER|SINGLE|BGA|8PIN|PLASTIC |
| 中文描述： | 音頻放大器|單| BGA封裝| 8引腳|塑料 |
| 文件頁數(shù)： | 6/10頁 |
| 文件大?。?/td> | 323K |
| 代理商： | LM4879IBP |
Application Information
BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 1, the LM4876 consists of two opera-
tional amplifiers. External resistors R
f
and R
i
set the closed-
loop gain of Amp1, whereas two internal 40k
resistors set
Amp2’s gain at -1. The LM4876 drives a load, such as a
speaker, connected between the two amplifier outputs, V
o
1
and V
o
2 .
Figure 1 shows that the Amp1 output serves as the Amp2 in-
put, which results in both amplifiers producing signals identi-
cal in magnitude, but 180 out of phase. Taking advantage of
this phase difference, a load is placed between V
1 and V
2
and driven differentially (commonly referred to as
″
bridge
mode
″
). This results in a differential gain of
A
VD
= 2 * (R
f
/R
i
)
Bridge mode is different from single-ended amplifiers that
drive loads connected between a single amplifier’s output
and ground. For a given supply voltage, bridge mode has a
distinct advantage over the single-ended configuration: its
differential output doubles the voltage swing across the load.
This results in four times the output power when compared
to a single-ended amplifier under the same conditions. This
increase in attainable output power assumes that the ampli-
fier is not current limited or that the output signal is not
clipped. To ensure minimum output signal clipping when
choosing an amplifier’s closed-loop gain, refer to the
Audio
Power Amplifier Design
section.
Another advantage of the differential bridge output is no net
DC voltage across the load. This results from biasing V
o
1
and V
o
2 at half-supply. This eliminates the coupling capaci-
tor that single supply, single-ended amplifiers require. Elimi-
nating an output coupling capacitor in a single-ended con-
figuration forces a single-supply amplifier’s half-supply bias
voltage across the load. The current flow created by the half-
supply bias voltage increases internal IC power dissipation
and may permanently damage loads such as speakers.
(1)
POWER DISSIPATION
Power dissipation is a major concern when designing a suc-
cessful bridged or single-ended amplifier. Equation (2) states
the maximum power dissipation point for a single-ended am-
plifier operating at a given supply voltage and driving a
specified output load.
P
DMAX
= (V
DD
)
2
/(2
π
2
R
L
) Single-Ended
However, a direct consequence of the increased power de-
livered to the load by a bridge amplifier is higher internal
power dissipation for the same conditions.
The LM4876 has two operational amplifiers in one package
and the maximum internal power dissipation is four times
that of a single-ended amplifier. Equation (3) states the maxi-
mum power dissipation for a bridge amplifier. However, even
with this substantial increase in power dissipation, the
LM4876 does not require heatsinking. From Equation (3),
assuming a 5V power supply and an 8
load, the maximum
power dissipation point is 633mW.
P
DMAX
= 4*(V
DD
)
2
/(2
π
2
R
L
) Bridge Mode
The maximum power dissipation point given by Equation (3)
must not exceed the power dissipation given by Equation
(4):
P
DMAX
= (T
JMAX
-T
A
) /
θ
JA
The LM4876’s T
= 150C. In the M08A package, the
LM4876’s
θ
is 140C/W. At any given ambient temperature
T
A
, use Equation (4) to find the maximum internal power dis-
(2)
(3)
(4)
sipation supported by the IC packaging. Rearranging Equa-
tion (4) results in Equation (5). This equation gives the maxi-
mum ambient temperature that still allows maximum power
dissipation without violating the LM4876’s maximum junction
temperature.
T
A
= T
JMAX
- P
DMAX
θ
JA
For a typical application with a 5V power supply and an 8W
load, the maximum ambient temperature that allows maxi-
mum power dissipation without exceeding the maximum
junction temperature is approximately 61C.
T
JMAX
= P
DMAX
θ
JA
+ T
A
For the MSOP10A package,
θ
= 210C/W. Equation (6)
shows that T
, for the MSOP10 package, is 158C for an
ambient temperature of 25C and using the same 5V power
supply and an 8
load. This violates the LM4876’s 150C
maximum junction temperature when using the MSOP10A
package. Reduce the junction temperature by reducing the
power supply voltage or increasing the load resistance. Fur-
ther, allowance should be made for increased ambient tem-
peratures. To achieve the same 61C maximum ambient
temperature found for the MO8 package, the MSOP10 pack-
aged part should operate on a 4.1V supply voltage when
driving an 8
load. Alternatively, a 5V supply can be used
when driving a load with a minimum resistance of 12
for the
same 61C maximum ambient temperature.
Fully charged Li-ion batteries typically supply 4.3V to por-
table applications such as cell phones. This supply voltage
allows the LM4876 to drive loads with a minimum resistance
of 9
without violating the maximum junction temperature
when the maximum ambient temperature is 61C.
The above examples assume that a device is a surface
mount part operating around the maximum power dissipation
point. Since internal power dissipation is a function of output
power, higher ambient temperatures are allowed as output
power or duty cycle decreases.
If the result of Equation (3) is greater than that of Equation
(4), then decrease the supply voltage, increase the load im-
pedance, or reduce the ambient temperature. If these mea-
sures are insufficient, a heat sink can be added to reduce
θ
. The heat sink can be created using additional copper
area around the package, with connections to the ground
pin(s), supply pin and amplifier output pins. When adding a
heat sink, the
θ
is the sum of
θ
,
θ
CS
, and
θ
. (
θ
is the
junction-to-case thermal impedance,
is the case-to-sink
thermal impedance, and
θ
is the sink-to-ambient thermal
impedance.) Refer to the
Typical Performance Character-
istics
curves for power dissipation information at lower out-
put power levels.
(5)
(6)
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is criti-
cal for low noise performance and high power supply rejec-
tion. Applications that employ a 5V regulator typically use a
10μF in parallel with a 0.1μF filter capacitors to stabilize the
regulator’s output, reduce noise on the supply line, and im-
prove the supply’s transient response. However, their pres-
ence does not eliminate the need for local bypass capaci-
tance at the LM4876’s supply pins. Keep the length of leads
and traces that connect capacitors between the LM4876’s
power supply pin and ground as short as possible. Connect-
ing a 1μF capacitor between the BYPASS pin and ground
improves the internal bias voltage’s stability and improves
the amplifier’s PSRR. The PSRR improvements increase as
the bypass pin capacitor value increases. Too large, how-
ever, and the amplifier’s click and pop performance can be
L
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| LM4879IBP/NOPB | 功能描述:IC AMP AUDIO PWR 1.1W MONO 8USMD RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Boomer® 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) |
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| LM4879ITLX | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:1.1 Watt Audio Power Amplifier |
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