Today, in an age of intense competitors, the challenge for item designers is to stay ahead of the pack and not just walk in lockstep with it. This ups the ante for system designers to introduce with set apart products.
One vital means to introduce is with high-density designs. In the promote smaller-footprint solutions, power system designers are currently focusing on the concern of power thickness– the outcome power per unit of location or volume of a power converter circuit.
One of the most visible example of DC/DC converter printed circuit board (PCB) layout for high thickness relates to power stage element placement as well as directing. Cautious layout could accompany better changing efficiency, reduced element temperature levels and decreased electromagnetic interference (EMI) signatures. Think about the power phase layout and also schematic in Figure 1.
Number 1: Four-switch buck-boost converter power stage layout and schematic
As I see it, these are the obstacles when developing high-density DC/DC converters:
● Part innovation. Improvements in component technology are key to minimizing general power dissipation, especially at higher switching regularities crucial for filter passive component dimension decrease. For example, power MOSFETs have actually seen consistent advancements in silicon and product packaging, most especially with the intro of gallium nitride (GaN) power devices with really reduced parasitics. On the other hand, magnetic part efficiency has actually progressed individually, albeit at a price perhaps lagging that of power semiconductors. Sensible layout of the control IC– with incorporated, adaptive gate drivers close to the MOSFETs– in some cases obviates the demand for switch-node voltage slew-rate change utilizing power-dissipating snubber or gateway resistor parts.
● Thermal design. While a high-density layout is usually favorable for conversion effectiveness, it might produce a thermal efficiency bottleneck. The same power dissipation in a smaller footprint ends up being untenable. Raised element temperature levels magnify worries of higher failing rates and reliability. Lower-profile power MOSFETs placed on the top side of the PCB– not airflow-shadowed by taller components like the inductor andelectrolytic capacitors– assistance thermal performance with convective air movement. For the converter in Figure 1, the inductor and electrolytics are deliberately situated under side of the multilayer PCB, because they would hinder warmth transfer if put on the top.
● EMI efficiency. EMI governing conformity is a key landmark in an item’s design cycle. A high-density design normally has little area available for EMI filtering. Nevertheless, tight layout enhances emitted discharges along with immunity to incoming disturbances. 2 essential steps are to lessen loophole areas consisting of high di/dt currents (see the white current courses in Number 1) and also decrease surface areas with high dv/dt voltages (see the SW1 and also SW2 copper polygons in Figure 1).
● High-density PCB design circulation. Plainly, it is necessary for power system designers to create and develop their PCB design skills. Although the layout obligations are frequently handed over to layout professionals, designers still bear the ultimate responsibility to evaluate the design as well as validate it.
With these challenges in mind, I lately wrote a three-part series for EDN labelled “DC/DC Converter PCB Layout” that delves into PCB layout thoroughly. It includes a listing of PCB layout guidelines structured as a checklist to assist developers during layout. The essential steps in the PCB design circulation for DC/DC converters are:
1. Select the PCB framework and stack-up requirements.
2. Determine the high di/dt present loops and high dv/dt voltage nodes from the schematic.
3. Perform power phase element layout and positioning.
4. Area the steering IC and finish the steering area layout.
5. Do important trace routing, consisting of MOSFET gate drive, current feeling, and output-voltage responses.
6. Design the power and GND planes.