Optimize PCB layout to improve converter performance

- Oct 20, 2018-

For switch mode converters, a good PCB layout is essential for optimal system performance.If the PCB is improperly designed, it may cause the following consequences: too much noise on the control circuit will affect the stability of the system;The system efficiency is affected by too much loss on the PCB trace line.Too much electromagnetic interference affects system compatibility.

ZXLD1370 is a multi-topology switch mode LED driver controller with external switching devices embedded in each different topology.The LED driver is suitable for buck, boost or buck - boost mode.

Taking the ZXLD1370 device as an example, this paper discusses the considerations of PCB design and provides relevant Suggestions.

Consider the trace width

For switching mode power supply circuits, the main switch and related power devices carry a large current.The trace lines used to connect these devices have resistances associated with their thickness, width, and length.The heat generated by the current passing through the trace not only decreases efficiency, but also increases the trace temperature.To limit temperature rise, it is important to ensure that the trace width is sufficient for rated switching current.

The following equation shows the relationship between temperature rise and the cross-sectional area of the trace.

Internal trace: I=0.024 x dT0.44 x A0.725

External trace: I=0.048 x dT0.444 x A0.725

Where: I= maximum current (A);DT = is higher than the environment temperature (℃);A= cross-sectional area (mil2).

Table 1 shows the minimum trace width of the relative current capacity.This is a statistical result based on a 20oC increase in trace temperature of 1oz/ft2 (35 sheets m) copper foil.