S32K144 Use PDB0 back to back mode to tirgger ADC, but channle1 didn't work?

hi ,sir

    I want to use more than 20 ADC channles, I configured  ADC0 channle 0 to 13, and ADC1 channle 0 to 7, Use PDB as tirgger source, set PDB0 channle 0 and PDB1 channle 0 work at back to back mode ,it can work well, and also set PDB0 channle 1 as back to back mode , but PDB0 channle 1 did't work at one time, i tried to disable PDB0 channle0 ,the PDB0 channle 1 can work well, what the problem it is ?  it seems like PDB0 can only work with one channle at the same time , i want to know how to PDB0's all channles get work ,the development tool what i use is S32DS SDK. please help me to find the problem ,thanks very much!