Innovation and Integration in DC-to-DC Regulators

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Integration continues to be the most important trend for designers of digital ICs. Integration is now the de facto strategy for offsetting the continuing decline in pricing for components.

For analog IC design, integration has not moved as quickly to the need for bulky passives such as inductors and capacitors. And, in spite of their higher efficiency, today’s cell phones and car entertainment systems continue to use less efficient linear regulators for performing DC-to-DC conversions. This choice is because linear regulators, unlike switching regulators, do not require a large inductor to make possible the voltage conversion. Figure 1 compares the circuitry of a linear regulator and a buck switching regulator.

 

 

Doing without an inductor and still attaining high-conversion efficiencies is important for power designers. A new strategy has been for designers to shrink the inductor size by switching at faster frequencies. Until very recently, switching regulators all operated with frequencies of about 100kHz. Buck regulators, operating at 100kHz, normally use inductors in the range of 47ΩH. By contrast, switching regulators, operating at 1MHz, just need 4.7ΩH of inductance. Assuming everything else is equal, this solution would reduce the volume of the required inductor by 90 percent. A low profile 4.7ΩH inductor that delivers 500mA continuously, normally has a footprint of around 4mm x 4mm and a profile height of around 2mm. A switching regulator IC is usually a 3mm x 3mm x 1mm package and therefore much larger compared to an advanced 500mA linear regulator such as Micrel’s tiny 2mm x 2mm x 0.9mm MIC5319.

 

 

The need for smaller inductors in space sensitive applications has led analog IC manufacturers to design switching regulators with faster and faster frequencies. In 2006, Micrel finally broke the 1ΩH barrier for 500mA switching regulators by launching the industry’s first 8MHz buck regulator. This solution features a tiny 0.47ΩH chip inductor that measures a mere 1.25mm x 2mm x 0.55mm; another 95 percent reduction in inductor volume compared to a 1MHz solution (see to Figure 2). The inductor has shrunk 200 times in volume compared to the 100kHz converter. Micrel recently began sampling a completely inductorless, high efficiency buck switching regulator.

The device, the MIC3385, is rated for up to 500mA and comes in a tiny 3mm x 3.5mm x 0.9mm MLF®* package. Efficiency is up to 90 percent and output noise and transient performance are excellent because the fixed mode frequency operation is supported with a light load LDO that assists the switcher during demanding load transients. Figure 3 shows Micrel’s MIC3385 noise and transient performance in comparison to an industry standard buck regulator with a PFM light load scheme. The noise on the MIC3385 is virtually immeasurable. At loads of about 30mA, PFM mode part generates a different band of noise with about 190mV of peak-to-peak deviation while the MIC3385 is still low noise. The load transition from PFM-to-PWM mode is where the largest deviation in output voltage is seen on the industry standard part. In Micrel’s MIC3385, the LDO mode supports the switcher in this transition and the overall output voltage drop is controlled well. Using small output capacitors that further integrate the solution, allows for exceptional overall transient and noise performance. To achieve the same in performance, the industry standard part would need five times the output capacitance.

 

 

Conclusion
The continuing trend is for smaller and more integrated analog and digital IC solutions. This makes it crucial for designers to switch from inefficient linear regulators to high efficiency, small solution size DC-to-DC switching regulator solutions. Micrel has demonstrated the viability of a breakthrough inductorless 500mA switching regulator that also allows shrinking the output capacitors while maintaining remarkable efficiency, low noise and exceptional transient performance.

*MLF is a registered trademark of Amkor Technology

 

 

 Featured Products

Part Number		Description	Data Sheet	App. Notes
MIC3385YML TR		8MHz Power System Module with LDO Standby Mode
MIC5319YML TR		500mA µCap Ultra-Low Dropout, High PSRR LDO Regulator

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