LM5122-Q1: Output voltage of LM5122+CSD19532Q5B is pulled down when the connect a heavier load

Hi Expert,
When customer is using the LM5122+CSD19532Q5B scheme to boost the voltage, VIN=12V, VOUT=70V, Fsw=110Khz, and it can work normally with a 100R load;
when the load resistance drops to 70R, the output voltage is pulled down to about 15V, which is not normal jobs. The target output power is 150W. 
The following is our circuit schematic diagram, Could you help us on that? Thanks.




Best Regards
Songzhen Guo