TPS4811-Q1: The back to back FET topology MOSFETs cannot be turn on

Hi team,

I follow TPS48111Q1EVM schematic to design a back to back FET topology to support bi-directional current flow application. The schematic as figure.

I check the charge pump operation waveform as below. Looks working well. Only one difference with the datasheet is EN signal is ramp up with the VS. 

Checking the startup behavior as below. As you can see the VBST and VPU didn't rising to the proper level as datasheet figure 9-3 described.

I trying to increase the CBST from 470nF to 4.7uF, and increase the gate resistor values. Both og changes didn't help to resolve this issue. 

Also, measure the FLT_T and FLT_I fault indictors can saw any falut happened. I need your help to resolve this issue. Please help to review the schematic design, and there any signals that I can measure the diagnostic and failure symptom. 

Thanks.

Muhsiu