The P1010 USB controller uses VBUSCLP input as input for detection VBUS voltage.
The P1010 USB controller hardware provides correct working if voltage on this pin is in range into 0v to 1.37V.
Therefore external voltage divider in Vbus usually is used to reduce the voltage range into 0v to 1.37V (external vbus divider ratio is 0.2626).
Factory recommends using divider with precise 51.1k / 18.2k.
This divider is needed if the P1010 USB PHY is not used.