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电源芯片TPS74401使用过程中出现问题

Other Parts Discussed in Thread: TMS320C6678, UCD9222, UCD7242, TPS74401

尊敬的TI工程师您好,我的电源模块应用中采用UCD9222+UCD7242和TPS74401为TMS320C6678这款多核DSP芯片供电,其中UCD9222+UCD7242已经能正常输出DSP的核电压(CVDD和DVDD),UCD9222的Powergood脚UCD_PG也已经拉高,并且作为TPS74401的EN使能信号。TPS74401的VIN是2.5V,VBIAS是3.3V,反馈电阻是按照1.8V的输出电压设置的3.57K和2.87K。2.5V和3.3V是上电就有的,TPS74401的使能信号相对于2.5V和3.3V来说有20ms左右的延迟,因为DSP上电顺序里面要求核电压好了以后才能上1.8V的。上电后,发现TPS74401输出电压在1.86V左右,但是TPS74401的Powergood脚始终是低电平,说明芯片工作状态不正常。随后,我尝试用fusion digital power designer的GUI软件拉低UCD_PG,使得TPS74401的EN使能信号为低电平,发现仍然能输出1.61V左右的电压,Powergood脚还是低电平。芯片的硬件配置是按照官方数据手册的配置来设计的,这个芯片外围电路不复杂,查来查去找不到原因,请您帮我看看哪里出了问题,谢谢!