Optimizing PCB layout improves converter performance

For switching mode converters, excellent lolomi laupapa matagaluega (PCB) layout is critical for optimal system performance. If PCB design is improper, it may cause the following consequences: too much noise to the control circuit and affect the stability of the system; Excessive losses on PCB trace line affect system efficiency; Causing excessive electromagnetic interference and affecting system compatibility.

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

ipcb

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 supply circuits, the main switch and associated power devices carry large currents. Traces used to connect these devices have resistances related to their thickness, width, and length. The heat generated by the current flowing through the trace not only reduces efficiency but also raises the temperature of the trace. To limit temperature rise, it is important to ensure that the trace width is sufficient to cope with the rated switching current.

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

Internal trace: I= 0.024× DT & 0.44 TImes; O se 0.725

I= 0.048× DT & 0.444 TImes; O se 0.725

Where, I= maximum current (A); DT = temperature rise higher than the environment (℃); A= cross-sectional area (MIL2).

Table 1 shows the minimum trace width for the relative current capacity. This is based on the statistical results of 1oz/ FT2 (35μm) copper foil with trace temperature rising 20oC.

Table 1: External trace width and current capacity (20 ° C).

Table 1: External trace width and current capacity (20 ° C).

For switching mode power converter applications designed with SMT devices, the copper surface on the PCB can also be used as a heat sink for power devices. Trace temperature rise due to conduction current should be minimized. It is recommended that trace temperature rise be limited to 5 ° C.

Table 2 shows the minimum trace width for the relative current capacity. This is based on the statistical results of 1oz/ft2 (35μm) copper foil with trace temperature rising 5oC.

Table 2: External trace width and current capacity (5 ° C).

Table 2: External trace width and current capacity (5 ° C).

Consider trace layout

The trace layout must be properly designed to achieve the best performance of the ZXLD1370 LED driver. The following guidelines enable ZXLD1370 based applications to be designed for maximum performance in both buck and boost modes.