本帖最后由 airwill 于 2017-4-21 06:23 编辑
TXB0108 是一个性能非常好的电平转换器件. 内部还使用 one shut 电路来提升信号的转换速度.不过它对应用的要求也挺高, 特别是输入的驱动能力. 我想楼主的问题应该就在这里
8.3.2 Input Driver Requirements
For proper operation,the device driving the data I/Os of the TXB0108 must have drive strength of at least ±2mA
关于上下拉电阻
8.3.5 Pullup or Pulldown Resistors on I/O Lines
The TXB0108 is designed to drive capacitive loads of up to 70 pF. The output drivers of the TXB0108 have low dc drive strength. If pullup or pulldown resistors are connected externally to the data I/Os, their values must be kept higher than 50 kΩ to ensure that they do not contend with the output drivers of the TXB0108. For the same reason, the TXB0108 should not be used in applications such as I2C or 1-Wire where an open-drain driver is connected on the bidirectional data I/O. For these applications, use a device from the TI TXS01xx series of level translators.
这里明白的说明, 信号线上不允许使用 上下拉电阻来强制高阻条件下的电平 (不低于 50K).
This device can only translate push-pull CMOS logic outputs. If for open-drain signal translation, please refer to TI TXS010X products.
总结: 由于双向传输存在互锁方面的问题, 各种器件都有解决办法. 这个器件采用边沿检测和脉冲驱动的办法实现信号转变, 这样要求输入信号有较强的驱动能力, 也就是在 TXB0108 的输出信号上输出相反信号(超过 TXB0108 的输出能力).
为此: 你可能需要增加一个驱动缓冲去驱动 TXB0108
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楼主
