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The LM4765 possesses a mute and standby function with internal
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 LM4765, a “level 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 Rc 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. Rshift, along with Cshift, creates
an RC time constant that reduces transients when the mute
or standby functions are enabled or disabled. Additionally,
Rshift limits the current supplied by the internal logic gates of
the LM4765 which insures device reliability. Refer to the
Mute Mode and Standby Mode sections in the Application
Information section for a more detailed description of these
functions.
翻译之后:
LM4765具有静音和待机功能
逻辑门是半电源参考。因此,要
使能静音或待机功能,电压为
这些引脚必须至少在半电源以上2.5V。在
单电源系统,微处理器等设备
和简单的逻辑电路用于控制静音和
备用函数,通常引用接地,而不是
half-supply。因此,要使用这些器件来控制逻辑
LM4765的电路,一个“电平移位器”,如图所示
必须使用图5。不需要电平移位器
分路供电配置,因为地面也是半供电。
当“逻辑输入”节点的电压为0V时,2N3904
是“关闭”,因此电阻Rc拉静音或备用输入到
供应。开启静音或待机功能。当
逻辑输入为5V, 2N3904为“on”,因此,
集电极上的电压基本上是0伏。这将禁用
静音或待机功能,因此放大器将在
它的正常运作模式。Rshift和Cshift一起创建
一个RC时间常数,当静音时减少瞬态
开启或关闭备用功能。此外,
的内部逻辑门提供的电流受到Rshift的限制
LM4765,确保设备的可靠性。参考
应用程序中的静音模式和待机模式部分
信息部分,以获取更详细的描述
功能。
最近在做一套电子分频2.1桌面系统,选定功放IC为LM4765,打算利用液晶屏背光供电作逻辑信号控制待机功能,替代220V电源开关(待机功耗约0.36W),阅读官方文档后产生疑问,文档说明和待机功能参数似乎相矛盾,以上文档我的理解,图三里逻辑输入电压为0V时开启静音或待机功能,逻辑输入为5V时放大器处于正常工作模式,但是图二参数表格里又有这样一段文字:
Standby Low Input Voltage 待机低输入电压
Not in Standby Mode 0.8 V (max) 未待机0.8 V(最大)
Standby High Input Voltage 待机高输入电压
In Standby Mode 2.0 2.5 V (min) 待机模式2.0 2.5 V (min)
未待机0.8 V(最大),工作状态最大0.8V? 待机模式2.0 2.5 V (min),待机模式电压2V-2.5V?这跟上述文档说明的意思完全相反,请各位帮忙看看,究竟是低电平待机还是高电平待机?
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