Resistance in the PoC power path can cause significant power loss, especially when there is a large amount of current being drawn in the system. Power loss can be minimized by increasing the PoC voltage level and reducing the amount of current being sent through the PoC network. But for applications that do not have a high voltage rail available or do not include components that can handle high voltages, reducing current draw may not be possible. The only alternative is to reduce resistance in the PoC power path.

There are three main factors that contribute to resistance in the power path.

1. DC resistance (DCR) of the inductors in the PoC network
2. Resistance of the cables
3. Resistance of the PCB traces

Each inductor has a max DCR specification in the data sheet. This DC resistance can add up to a significant total resistance across two PoC networks being used in a full system. Typically, smaller inductors have higher DCR than larger inductors. Check the data sheet of each inductor and choose components that have a balance between the desired size of the overall PoC network and the allowable loss in the total power system. See Section 6 for a list of PoC networks and inductors reviewed by TI.

Cables introduce a small amount of resistance in the total power path. Cable data sheets quantify resistance in units of ohms per kilometer. Depending on the cable type and the length of the cable, the total resistance of the cable can be calculated. Typically, thicker cables have less resistance per kilometer than thinner cables. Please check the cable data sheet for full details.

The PCB traces also add a small amount of resistance in the power path. The equations below can be used to estimate the resistance for the PCB portion of the system:

R_ref = The total electrical resistance of the PCB trace (assuming 20°C for room temperature)

ρ = The intrinsic electrical resistivity of the conducting material. This characteristic is affected by temperature. At 20°C, the resistivity of copper is typically 1.68x 10?? Ω·m.

L = Length of the trace (meters)

t = Thickness of the trace. 1 ounce of copper thickness is typically 35μm thick (0.000035 meters)

W = Width of the trace (meters)

R_op = The total electrical resistance of the PCB trace at a specific operating temperature.

α = Temperature coefficient of resistivity for the conducting material (0.00393 for copper)

T_op = Operating temperature of the system

T_ref = Reference temperature (20°C for room temperature)