For switching mode converters, a good PCB layout is essential for optimal system performance.
If the PCB is improperly designed, the following consequences may be caused: too much noise will be generated on the control circuit and the stability of the system will be affected;
Excessive loss on PCB trace line will affect system efficiency.
Too much electromagnetic interference will affect the compatibility of the system.
ZXLD1370 is a multi-topology switching mode LED drive controller, with external switching devices embedded in each different topology.
The LED drive is suitable for step-down, step-up or step-down mode.
This paper will take ZXLD1370 device as an example to discuss the considerations of PCB design and provide relevant Suggestions.
Consider the trace width
For switching mode power circuits, the main switches and associated power devices carry large currents.
The trace lines used to connect these devices have resistance associated with their thickness, width and length.
The heat generated by the current flowing through the trace not only reduces the efficiency, but also increases the temperature of the trace.
To limit the temperature rise, it is important to ensure that the trace width is wide enough to handle the rated switching current.
The following equation shows the relationship between temperature rise and cross - sectional area of trace line.
Internal trace: I=0.024 * dT0.44 * A0.725
External trace: I=0.048 * dT0.444 * 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 relative current capacity.
This is based on the statistical results of 1oz/ft2 (35 degrees Celsius) copper foil at a temperature of 20oC.
For switching mode power converters designed with tabbed devices, the copper surface on the PCB can also be used as a radiator of power devices.
The temperature rise of the trace due to conduction current should be minimized.
It is recommended to limit the temperature rise of trace line to below 5oC.
Table 2 shows the minimum trace width of relative current capacity.
This is based on the statistical results of 1oz/ft2 (35 degrees Celsius) copper foil at a 5oC increase in trace temperature.