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ADS1299 双极性电压被拉成0

Other Parts Discussed in Thread: ADS1299-4

+2.5V和-2.5V。按evm参考电路画的。-2.5V被拉成+0.6V。+2.5V正常。取下芯片后-2.5V正常。焊上芯片就变成+0.6V。采用内部晶振。(如果采用单极性电源+5V和0V,电压正常,但下面的VCAP输出不正常,都严重偏大)

VCAP1=+1.66V,VCAP2=+1.5V,VCAP3=4.2V,VCAP4=+0.7V。

单板只上电。程序未进行初始化配置。电路硬件默认RESET  PWDN默认上拉。电路图如下:电源部分和EVM参考原理图完全一样。

急求,各位老大帮看下,是什么原因呢?多谢了!