High Density PCB Layout of DC/DC Converters, Part 1

Today, in an age of extreme competition, the difficulty for item designers is to remain in advance of the pack as well as not just walk in lockstep with it. This ups the stake for system designers to innovate with distinguished products.

One crucial way to innovate is with high-density layouts. In the promote smaller-footprint options, power system developers are now concentrating on the concern of power density– the result power each of location or volume of a power converter circuit.

The most noticeable instance of DC/DC converter printed motherboard (PCB) design for high density relates to power phase part placement and transmitting. Cautious format can accompany far better changing efficiency, reduced part temperature levels as well as reduced electro-magnetic interference (EMI) trademarks. Think about the power phase format as well as schematic in Figure 1.

Figure 1: Four-switch buck-boost converter power stage layout as well as schematic

As I see it, these are the difficulties when designing high-density DC/DC converters:

● Component modern technology. Developments in element modern technology are key to minimizing total power dissipation, especially at greater switching frequencies important for filter passive component size reduction. For instance, power MOSFETs have actually seen regular advances in silicon as well as packaging, most especially with the introduction of gallium nitride (GaN) power tools with really low parasitics. Magnetic element performance has actually advanced individually, albeit at a rate arguably delaying that of power semiconductors. Prudent layout of the steering IC– with integrated, adaptive entrance motorists near the MOSFETs– in most cases prevents the demand for switch-node voltage slew-rate modification making use of power-dissipating snubber or entrance resistor components.

● Thermal design. While a high-density layout is typically favorable for conversion performance, it might produce a thermal performance bottleneck. The very same power dissipation in a smaller sized footprint comes to be illogical. Raised component temperature levels enhance worries of higher failing rates and also dependability. Lower-profile power MOSFETs put on the top of the PCB– not airflow-shadowed by taller parts like the inductor andelectrolytic capacitors– help thermal performance with convective airflow. For the converter in Figure 1, the inductor and electrolytics are intentionally located under side of the multilayer PCB, since they would certainly restrain heat transfer if put on the top.

● EMI performance. EMI regulatory conformity is an essential landmark in a product’s design cycle. A high-density design commonly has little space available for EMI filtering system. Tight format boosts radiated exhausts as well as immunity to inbound disruptions. Two necessary steps are to lessen loop locations consisting of high di/dt currents (see the white existing paths in Figure 1) and also lower surface locations with high dv/dt voltages (see the SW1 and SW2 copper polygons in Figure 1).

● High-density PCB design flow. Clearly, it’s crucial for power system developers to establish and develop their PCB design abilities. Although the format duties are usually handed over to design experts, engineers still bear the utmost duty to examine the design and accept it.

With these difficulties in mind, I recently wrote a three-part series for EDN labelled “DC/DC Converter PCB Layout” that dives into PCB layout carefully. It consists of a listing of PCB design standards structured as a list to assist designers throughout design. The important steps in the PCB design flow for DC/DC converters are:

1. Select the PCB framework and stack-up spec.
2. Determine the high di/dt current loopholes and also high dv/dt voltage nodes from the schematic.
3. Execute power phase component format and also positioning.
4. Place the steering IC and also complete the steering section format.
5. Perform essential trace routing, consisting of MOSFET entrance drive, existing feeling, as well as output-voltage feedback.
6. Design the power and also GND planes.

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