To attain higher overall efficiency and faster-charging ability, the 800V battery system is replacing the 400V battery system as the mainstream technological route for battery electric vehicles(BEVs). However, the construction speed of charging piles supporting the 800V battery system is currently slow. To adapt the low-voltage charging piles to support the DC fast charging of 800V battery, this paper proposes a motor phase-access integrated boost charging scheme, which does not require additional power components and special interfaces compared to existing schemes. For this scheme, this paper analyzes the charging torque of the interior permanent magnet synchronous motor at different electrical angles, and proposes the optimal charging position. For switching mode analysis and design, the current ripple performance of the two-phase synchronous mode and the interleaved mode are compared, and the interleaved switching mode is recommended. Finally, the integrated charging function of 80kW under the existing BEV platform is realized with a motor efficiency of over 98%, and the theoretical analysis results are verified by experiments.