请教----open drain

ponysea

很多IC 的“data sheet”上面对于一些IO口的定义有“open drain”一说，哪位老兄帮忙解释一下下这个东东是什么意思？
先行谢过！

aquasnake

<P>漏极开路，如果作为IO，需要上拉电阻]</P>[br]<p align=right><font color=red>+3 RD币</font></p>

deann

如果需要边沿时序，上拉电阻的值需要注意。另外电源选取和目的IO相同。[br]<p align=right><font color=red>+3 RD币</font></p>

xdtony

<P>可以将其理解为一个一端接地的开关，有很好的灌电流特性，适合驱动大电流器件，例如键盘背光、震动马达等，不适合用作GPIO（即使加了上拉电阻）。</P>[br]<p align=right><font color=red>+5 RD币</font></p>

niles

<P>学习了。谢谢各位！</P>

ponysea

<DIV class=quote><B>以下是引用<I>xdtony</I>在2005-11-3 17:51:53的发言：</B>

<P>可以将其理解为一个一端接地的开关，有很好的灌电流特性，适合驱动大电流器件，例如键盘背光、震动马达等，不适合用作GPIO（即使加了上拉电阻）。</P></DIV>


谢谢
我看到的data sheet上面是MOS管作为开关
这种口一般用作输出控制信号么
还是输出一些标志
不能用作输入是吧
但是对灌电流特性也是不葚了解
能再详细的解释一下么?
谢谢
[em01]

simon

<P>对比三极管电路，相当于输出口接在集电极</P><P>如基极为高，可对外输出低电平信号；但无法输出高电平，需要上拉电阻。</P><P>目的是为了方便使用者上拉到自己想要的电压以保证满足两边的电平要求</P><P>典型如I2C总线</P>[br]<p align=right><font color=red>+5 RD币</font></p>

l87522

最大的作用就是可以用作“线与”和电平转化。

zjrd

OC可以实现“线与（wire-and)”而不会对电路有损害

pengjq

<P>Open-collector/open-drain is a circuit technique which allows multiple devices to communicate bi-directionally on a single wire. <P>Open-collector/open-drain devices sink (flow) current in their low voltage active (logic 0) state, or are high impedance (no current flows) in their high voltage non-active (logic 1) state. These devices usually operate with an external pull-up resistor that holds the signal line high until a device on the wire sinks enough current to pull the line low. Many devices can be attached to the signal wire. If all devices attached to the wire are in their non-active state, the pull-up will hold the wire at a high voltage. If one or more devices are in the active state, the signal wire voltage will be low. <P>An open-collector/open-drain signal wire can also be bi-directional. Bi-directional means that a device can both output and input a signal on the wire at the same time. In addition to controlling the state of its pin that is connected to the signal wire (active, or non-active), a device can also sense the voltage level of the signal wire. Although the output of a open-collecter/open-drain device may be in the non-active (high) state, the wire attached to the device may be in the active (low) state, due to activity of another device attached to the wire. <P>The bi-directional nature of an open-collector/open-drain device is what makes this circuit so important in interconnecting many devices on a common line. The I2C Bus and SMBus uses this technique for connecting up to 127 devices. <P>Open-drain refers to the drain terminal of a MOS FET transistor. Open-collector is the same concept on a bipolar device.
  </P>[br]<p align=right><font color=red>+5 RD币</font></p>