你好，我這邊測試CH552時發(fā)現(xiàn)了失效的問題。芯片正常使用了幾周，之后出現(xiàn)了失效。萬用表測量管腳似乎都正常。

具體失效的原因沒有找到，但是癥狀是USB無法識別。將D+上拉10K到5V會報(bào)Device Descriptor Request Fail錯誤。

原理圖：

用戶程序在開始時先初始化USB和串口，再將板載LED管教P3.3置為輸出低電平。所以正常情況下，按住按鈕上拉D+進(jìn)入引導(dǎo)程序，LED會亮。不按按鈕進(jìn)入用戶程序，LED會亮很短的時間然后熄滅。

對于失效的芯片。無論按不按按鈕，LED都會亮很短的時間然后熄滅。P1.5拉低也一樣。似乎沒有進(jìn)入引導(dǎo)程序。

以下是上電時USB的信號：

D+以3.27V持續(xù)了8ms，再以2.13V持續(xù)了100ms。應(yīng)該是電壓不夠沒有觸發(fā)主機(jī)（Win11）的識別。USB上沒有出現(xiàn)任何數(shù)據(jù)，設(shè)備管理器也沒有識別到任何硬件。

如果按住按鈕，把D+上拉10K到5V，會有以下的信號：
D+以3.8V持續(xù)了2ms，再以3.2V持續(xù)了100ms。主機(jī)開始輸出同步信號，主機(jī)嘗試了三次發(fā)出Get_descriptor信號，并在2.2s后放棄。CH552似乎沒有任何回復(fù)。

請問這種失效大概是什么原因，是否有辦法可以修復(fù)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 - 沁恒微電子社區(qū)

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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