Limitations of Sense Lines

Recommended Design Rules and Strategies for BGA Devices User Guide (UG1099)

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Voltage Disparity

Because sense lines can only be placed at one location at the point-of-load, other areas in front of the sense points might show a higher voltage, while points beyond the point-of-load might see lower voltage. The following figure illustrates this voltage disparity. As the current flows from the VRM to the point-of-load, the voltage at point V1 is higher than the sense point at V2. Likewise, the voltage at point V3 is lower than at the sense point V2.

Figure 1. Voltages at Various Points in BGA Pin Field

VRMs with Only One Sense Pin

Some VRMs do not include a sense pin for ground. The primary limitation of this arrangement is that fluctuations in the ground voltage at the point-of-load are not accounted for by the VRM, resulting in less precise voltage regulation.