Why Optimize Buck Regulators for 8V-18V Operation?

Over the past few months, I have published a few articles discussing the advantages of our soft turn on ZVS Buck topology when it is applied to a wide ranging (8V-36V) input voltage combined with large step down ratios of as much as 36:1. Our PI33xx series of DC-DC converters provide best in class efficiency at higher input voltages by full utilization of the ZVS topological benefits, with heavy emphasis on zero voltage turn on of the high side MOSFET. The performance of our PI33xx has been so well received that many customers have asked us “How can your new topology help us with lower input voltage conversion that is rather limited in range?”

This is an excellent question. While most Engineers can readily understand that reduction of the drain to source voltage by 90% at 36V input (switching at 1MHz) can save 0.65W in power loss due to parasitic capacitance (1nF) of the high side MOSFET alone, the benefit of the same reduction in a 12V application results in less than 73mW. So how does the ZVS topology improve a lower voltage application? In the ZVS topology, zero voltage turn on is only part of the benefits. Zero current switching is also a main part of the topology.

The ZVS topology applied to lower voltage inputs still prevents body diode conduction of the parasitic diode of the synchronous MOSFET PRIOR to turn on of the high side MOSFET. This is achieved by throttling back energy storage just enough to provide softer switching than conventional regulators and elimination of the body diode conduction. Lower voltage means lower voltage MOSFET’s with lower on resistance which reduces RMS conduction losses while having less penalty in high side gate drive losses due to partial ZVS resonant turn on. Variable frequency operation allows a high efficiency over a wide dynamic range, with internal losses and inductor losses very well balanced. Figures 1 and 2 provide a side by side comparison between the PI3301-X1 and the low voltage counterpart PI3423 3.3V output. The PI3424 5V version is also introduced that produces a whopping 75W at 96% efficiency.

ZVS Buck Regulators

Figure 1 PI3301-X1 3.3V Efficiency

 

ZVS Buck Regulators

Figure 2 PI34XX Efficiency

The buck regulators provide a host of benefits for the designer including:

  • Operating Range
    • Vin (8 – 18 V) and with widely trimmable Vout (1 – 5 V)
    • -40°C to 125°C operating range
  • High Efficiency
    • >96% peak 12 V to 5 V @ 75W
    • Light load and full load high efficiencySimple to Use -> Fast Development Time
  • 10 x 14 x 2.6 mm LGA SiP package

Thanks for your attention and see you next time.

For more information and to register for an evaluation board, go to Picor Cool-Power ZVS Buck Regulator

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