When the charging or discharging current of lithium battery is higher than 10A,why does the output voltage fluctuate and the SS pin of ADP1972 also change?
Without more information about the application circuit and the test setup it is difficult to answer your question. The SS pin voltage is generated by a constant current source charging a capacitor when the ADP1972 is enabled. This makes the PWM duty cycle gradually increase in relation to the SS pin voltage in order to limit inrush current from the DC bus. Once the SS capacitor is fully charged, the voltage on the SS pin should remain around 5V.
The only information I have to go on is that the Output voltage and SS voltage fluctuate at high current, with this information the only thing I can suggest is to look at the DC Bus voltage and make sure it is not dropping out due to overcurrent. If the power supply that is providing the input power cannot sustain the required input current, the power supply will limit current and cause a drop in bus voltage that could cause both of the described conditions.