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UCC28780: 芯片VDD到达启动阈值VDDon后不启动,SWS引脚的电压不下降至11V,RUN引脚不使能

Part Number: UCC28780

芯片VDD到达VDDon=18V后,芯片不发波,RUN引脚输出为0,测量HVG引脚和SWS引脚,其电压也没有在VDDon后自动下降,请问芯片到达VDDon后HVG和SWS会自动下降至11V吗,焊接的是新的芯片,如果没有下降是芯片损坏还是电路配置问题呢?