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| 型號(hào)： | LM4700DWF |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 30 W, 1 CHANNEL, AUDIO AMPLIFIER, UUC |
| 封裝： | WAFER |
| 文件頁(yè)數(shù)： | 5/19頁(yè) |
| 文件大?。?/td> | 558K |
| 代理商： | LM4700DWF |
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Application Information (Continued)
The LM4700 possesses a mute and standby function with in-
ternal logic gates that are half-supply referenced. Thus, to
enable either the mute or standby function, the voltage at
these pins must be a minimum of 2.5V above half-supply. In
single-supply systems, devices such as microprocessors
and simple logic circuits used to control the mute and
standby functions, are usually referenced to ground, not
half-supply. Thus, to use these devices to control the logic
circuitry of the LM4700, a “l(fā)evel shifter”, like the one shown
in
Figure 5, must be employed. A level shifter is not needed
in
a
split-supply
configuration
since
ground
is
also
half-supply.
When the voltage at the Logic Input node is 0V, the 2N3904
is “off” and thus resistor R
C pulls up mute or standby input to
the supply. This enables the mute or standby function. When
the Logic Input is 5V, the 2N3904 is “on” and consequently,
the voltage at the collector is essentially 0V. This will disable
the mute or standby function, and thus the amplifier will be in
its normal mode of operation. R
SHIFT, along with CSHIFT, cre-
ates an RC time constant that reduces transients when the
mute or standby functions are enabled or disabled. Addition-
ally, R
SHIFT limits the current supplied by the internal logic
gates of the LM4700 which insures device reliability. Refer to
the Mute Mode and Standby Mode sections in the Applica-
tion Information section for a more detailed description of
these functions.
CLICKS AND POPS
In the typical application of the LM4700 as a split-supply au-
dio power amplifier, the IC exhibits excellent “click” and “pop”
performance when utilizing the mute and standby functions.
In addition, the device employs Under-Voltage Protection,
which eliminates unwanted power-up and power-down tran-
sients. The basis for these functions are a stable and con-
stant half-supply potential. In a split-supply application,
ground is the stable half-supply potential. But in a
single-supply application, the half-supply needs to charge up
just like the supply rail, V
CC.
This makes the task of attaining a clickless and popless
turn-on more challenging. Any uneven charging of the ampli-
fier inputs will result in output clicks and pops due to the dif-
ferential input topology of the LM4700.
To achieve a transient free power-up and power-down, the
voltage seen at the input terminals should be ideally the
same. Such a signal will be common-mode in nature, and
will be rejected by the LM4700. In
Figure 3, the resistor R
INP
serves to keep the inputs at the same potential by limiting the
voltage difference possible between the two nodes. This
should significantly reduce any type of turn-on pop, due to an
uneven charging of the amplifier inputs. This charging is
based upon a specific application loading and thus, the sys-
tem designer may need to adjust these values for optimum
performance.
As shown in
Figure 3, the resistors labeled R
BI help bias up
the LM4700 off the half-supply node at the emitter of the
2N3904. But due to the input and output coupling capacitors
in the circuit, along with the negative feedback, there are two
different values of R
BI, namely 10 k and 200 k. These re-
sistors bring up the inputs at the same rate resulting in a pop-
less turn-on. Adjusting these resistors values slightly may re-
duce pops resulting from power supplies that ramp
extremely quick or exhibit overshoot during system turn-on.
AUDIO POWER AMPLlFIER DESIGN
Design a 25W/8
Audio Amplifier
Given:
Power Output
25 Wrms
Load Impedance
8
Input Level
1 Vrms(max)
Input Impedance
47 k
Bandwidth
20 Hz to 20 kHz ± 0.25 dB
A designer must first determine the power supply require-
ments in terms of both voltage and current needed to obtain
the specified output power. V
OPEAK can be determined from
equation (4) and I
OPEAK from equation (5).
(4)
(5)
To determine the maximum supply voltage, the following
conditions must be considered. Add the dropout voltage to
the peak output swing V
OPEAK, to get the supply rail at a cur-
rent of I
OPEAK. The regulation of the supply determines the
unloaded voltage which is usually about 15% higher. The
supply voltage will also rise 10% during high line conditions.
Therefore the maximum supply voltage is obtained from the
following equation:
Max Supplies
≈ ± (V
OPEAK +VOD) (1 + Regulation) (1.1)
For 25W of output power into an 8
load, the required V
O-
PEAK
is 20V. A minimum supply rail of ±25V results from add-
ing V
OPEAK and VOD. With regulation, the maximum supplies
are ±31.7V and the required I
OPEAK is 2.5A from equation
(5). At this point it is a good idea to check the Power Output
vs Supply Voltage to ensure that the required output power is
obtainable from the device while maintaining low THD+N. In
addition, the designer should verify that with the required
power supply voltage and load impedance, that the required
heatsink value
θ
SA is feasible given system cost and size
constraints. Once the heatsink issues have been addressed,
the required gain can be determined from equation (6).
(6)
From equation (6), the minimum A
V is AV ≥ 14.14.
By selecting a gain of 21, and with a feedback resistor, R
F =
20 k
, the value of R
I follows from equation (7).
R
I = RF (AV 1)
(7)
Thus with R
J = 1k a non-inverting gain of 21 will result.
Since the desired input impedance was 47 k
, a value of
47 k
was selected for R
IN. The final design step is to ad-
dress the bandwidth requirements which must be stated as a
pair of 3 dB frequency points. Five times away from a 3 dB
point is 0.17 dB down from passband response which is bet-
DS012369-9
FIGURE 5. Level Shift Circuit
www.national.com
13
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PDF描述 |
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| LM4700MWC | 30 W, 1 CHANNEL, AUDIO AMPLIFIER, UUC |
| LM4700T | 30 W, 1 CHANNEL, AUDIO AMPLIFIER, PZFM11 |
| LM4700TF/NOPB | 30 W, 1 CHANNEL, AUDIO AMPLIFIER, PZFM11 |
| LM4701MWC | 30 W, 1 CHANNEL, AUDIO AMPLIFIER, UUC |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4700T | 功能描述:IC AMP AUDIO PWR 30W AB TO220-11 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) |
| 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 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) |
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