你好，我这边测试CH552时发现了失效的问题。芯片正常使用了几周，之后出现了失效。万用表测量管脚似乎都正常。

具体失效的原因没有找到，但是症状是USB无法识别。将D+上拉10K到5V会报Device Descriptor Request Fail错误。

原理图：

用户程序在开始时先初始化USB和串口，再将板载LED管教P3.3置为输出低电平。所以正常情况下，按住按钮上拉D+进入引导程序，LED会亮。不按按钮进入用户程序，LED会亮很短的时间然后熄灭。

对于失效的芯片。无论按不按按钮，LED都会亮很短的时间然后熄灭。P1.5拉低也一样。似乎没有进入引导程序。

以下是上电时USB的信号：

D+以3.27V持续了8ms，再以2.13V持续了100ms。应该是电压不够没有触发主机（Win11）的识别。USB上没有出现任何数据，设备管理器也没有识别到任何硬件。

如果按住按钮，把D+上拉10K到5V，会有以下的信号：
D+以3.8V持续了2ms，再以3.2V持续了100ms。主机开始输出同步信号，主机尝试了三次发出Get_descriptor信号，并在2.2s后放弃。CH552似乎没有任何回复。

请问这种失效大概是什么原因，是否有办法可以修复或者避免？

It seems the bootloader exits too soon. At least on pwron reset with pressed button it should stay there until the isp tool does exit. How do you enter the loader from user mode?

Your led switches off in usermode so i supose you always enter the user mode. That 2 ms may come from a timeout in the mainloop of the bootloader.

It may be a problem of a partly failed flash. I noticed that chips with loader >=2.31 flash failures may happen very early.

verify bug in WCHISPtool - 沁恒微电子社区

If the flashing at the usb vector fails the chip will never work again in usb mode. You know that every reprogramming of the flash eats 2 cycles because the loader alway erases the flash for security reasons.

Try to connect usb serial stick to SIO1 and activate serial programming that saved my ass on a ch559 once.

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