參數(shù)資料
型號(hào)： LM4753T
廠商： NATIONAL SEMICONDUCTOR CORP
元件分類： 音頻／視頻放大
英文描述： 11.8 W, 2 CHANNEL, AUDIO AMPLIFIER, PZFM15
封裝： TO-220, 15 PIN
文件頁(yè)數(shù)： 15/16頁(yè)
文件大?。?/td> 511K
代理商： LM4753T
Application Information (Continued)
If the sequence described above and shown in
Figure 4 is
not used, then the external circuitry shown in Figure 5 should
be used to minimize turn-on/off pops and protect the output
stage against SOA violations.
In
Figure 5 there are only a few components that are differ-
ent than the ones described earlier for lowpass filtering the
pin voltages. The new components are Q1, R2, R3, D1 and
D2. All of the other components will perform the same func-
tions that were previously described.
The explanation of how the circuit in
Figure 5 works will be
related to the timing waveforms in
Figure 6. The circuit in
Figure 5 protects the LM4753 from SOA violations by ensur-
ing that the enabling of the standby function when music is
playing will not quickly bring the biasing to ground before the
input signal is smoothly attenuated through the volume func-
tion. Again, this is important because any quick changes in
output current when driving an inductive load will cause a fly-
back voltage that may damage the IC.
As shown in
Figure 6, first notice that music is playing at the
output. When the mechanical standby switch is toggled from
ground (play mode) to 5V (standby mode), transistor Q1 is
quickly turned on, discharging capacitor C7, bringing the
voltage at the volume pin, pin 3, to ground. This quickly at-
tenuates the audio signal at the output as shown in
Figure 6.
While the input signal is being attenuated, the diode D1 be-
comes reverse biased and the voltage at the standby pin
starts to charge through R4, C8 and C9. There is also a finite
amount of current flowing through R5 as well, but because of
its high resistance, we can neglect it in the charge-up timing
of pin 9. Note that when the standby switch was grounded,
the diode D1 was clamping the standby pin low, setting the
initial voltage condition of C8 at a low voltage. Once C8
starts charging up, diode D2 becomes forward biased and
C9 also starts charging up. This brings the standby and mute
pin voltages up simultaneously. By the time the standby pin
voltage enables the standby function, the voltage at the vol-
ume pin will already have been ramped down to 0V and the
output signal will be close to 0V.
When the IC is in standby mode the biasing of the IC is
brought down to ground and the quiescent supply current is
around 7 mA. When the standby switch in
Figure 5 is toggled
DS100043-28
FIGURE 4. Turn-On/Off Sequence
www.national.com
8
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LM4755_02 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Stereo 11W Audio Power Amplifier with Mute
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LM4755T/NOPB 功能描述:IC AMP AUDIO PWR 11W AB TO220-9 RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:- 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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