App note from Richtek on comparison of different connection of Common-N DCR current sensing and its effect on PCB resistance mismatch. Link here (PDF)
It has been many years since GPU power solutions (OVR3i+ / OVR4i+) adopt common-N structure for DCR current sensing in multi-phase applications. There are two common-N type multi-phase controllers for graphic core power application in Richtek, the 3 phases controller RT8843A for OVR3i+ solution and the 8 phases controller RT8848A for OVR4i+ solution respectively. The common-N structure has benefit of pin-saving in a limited package size as compared to differential structure of DCR current sensing. However, this structure has an intrinsic drawback of current unbalance issue as PCB layout is not symmetric especially in high phase count applications. High phase count is a trend in computing graphic cards or data mining machines. The layout can’t always be symmetric in a limited board size and even the priority of high speed signal routing for GPU/DDR is much higher than power routing. Therefore, the effect of RPCB non-symmetric on current sensing is a crucial topic in multi-phase applications.