使用CH552E diy了一个小键盘，只焊接最小系统部分，电路焊接没问题，都用电流表打过了，5v和3.3v正常，第一次USB插到电脑里，没刷过程序，应该能进入bootloader模式，但是什么反应都没有，不显示设备，上拉DP到3.3V，显示未知设备，请求描述符失败。各位网友帮忙看一下是什么原因，谢谢了。难道是CH552E有问题？我又买了几片，准备换上试试。
原理图和PCB如下图所示：
芯片可以配置为P1.5接地作为进入bootloader的条件，注意是否在下载过程不小心配置了。
电路上，可以飞线把芯片P1.5引脚接地，再上电测试。
P1.4或者P1.5接地均无任何反应。 真是太奇怪了，外围电路这么简单的单片机为社么不能正常工作，难道是买的假单片机？
重新购买552，更换后，插入usb仍然没有任何反应，这个芯片把我整不会了。
A new empty CH552 will always enter the bootloader, so there must be something wrong with the usb connection. Check D+ and D- and the footprint of the usb-c connetor.
I am quite sure the footprint is mirrored!
reply 6#:
you are right, The 552 will always enter the boot loadwer when first use.
I have check my footprint, compare to the datasheet, it's right.the 552 at bottom layer in my pcb. if the footprint is wrong, the 3.3V output at pin 10 will wrong, but in my pcb is right. and i also check the connection for the D+ and D- with the usb line type-A side, it's also right. i'm very confused.
您好，
建议联系原厂申请个评估板试试： /services/sale_support.html
另外PCB设计上建议USB差分走线，建议尽量不要过孔，注意V33引脚出来的3.3V尽量不要与其他3.3V网络有关联，防止网络电压不稳定造成影响（不要用该引脚给其他3.3V芯片供电）
usb用立创eda差分走的4mil线，3.3V引出来是为用镊子短接到DP进入bootloader用，没用于供电。准备再画一版，加粗一点usb线试试，不打过孔试一下。
I dont believe the vias or usb traces are a problem in your design. Its just USB FS (12MHz).
Since you have checked D+ and D- connection to be correct. Do you have a second power source in your design? Maybe power travels through your serial port and prevents the CH552 from entering the bootloader. Remember the bootloader just gets activated on power on events.
Another thing: Since v2.5 loader there is a timeout on the connection but that should not react on a empty chip.
如usbman所说，检查下D+D-顺序，再就是从原厂获取芯片。
仔细检查了一遍，原理图D- D+没有问题，mcu我又重新购买了一次，同样问题，还是没有任何反应，进不了bootloader。我也参考了demo板的设计，并没有发现什么不同的地方，这也太奇怪了。
to 11# usbman: I just use usb as mcu power, just one power source.
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