盡量讓 buck OD (with N+ or P+, buck OD 做成guard ring (guard ring should be wide, contact number as many as possible), 防止Vbs (Vth) 飄移, Vbs = 0 ) 接近MOS的 Source (source OD with contact as many as possible). Source & body terminal as near as possible. 盡量讓 bulk OD & source OD 越近越好 以防止 latch up