TLVRs Overcome the Limits of Multi-Phase Devices Using Dual Coil Power Inductors

The world is thriving on semiconductor processors for high-performance systems capable of processing artificial intelligence, big data, and IoT applications. The ongoing miniaturization of processor transistors and decreasing power supply voltages presents product designers with power circuit configuration challenges, but these can be resolved with a trans-inductor voltage regulator (TLVR).

Semiconductor manufacturers have an incredible track record of squeezing more advancements into their CPU, GPU, and FPGA processors. Power supply voltages are decreasing while current consumption and overall power usage are increasing, but low-voltage power supplies come with an extremely small tolerance for voltage fluctuation. According to electronic components manufacturer TDK, if a core voltage needs to be supplied with an accuracy of ±3%, then a voltage of 1 V would require a tight control within ±30 mV.

Multi-phase voltage regulators with multi-phase duty regulation can manage sudden high-current loads, but must operate at high frequencies to switch between phases with reduced response time. With data center needs exceeding the limitations of existing multi-phase voltage regulator configurations, designers of server power supplies were running into challenges to create circuits that could operate at those higher frequencies.

Multi-phase TLVR circuit configurations, first described in 2019, have been quickly adopted to handle high-speed load fluctuation in low-voltage, high-current applications. The TLVR provides high response performance while minimizing power losses. The TLVR also cuts down on system costs and footprint by reducing the value of output capacitors.

Supply current simultaneously for multiple inductors

In a TLVR circuit, each phase switch is connected to an inductor with an added secondary winding, and each of those is connected in a series loop with a compensating inductor. To accommodate surges in current demand, the circuit can supply current simultaneously from all inductors without significantly lowering the power supply voltage.

TDK's VLBUC series of dual coil power inductors are designed for use with TLVRs to improve voltage regulator load response, and be compliant with the voltage regulator specifications of the VR14 server generation to operate reliably under variable current demands.

The company's VLBUC12060120R15LF3 (Figure 1) is one of a series of dual wire-wound, ferrite-coil power inductors that can handle large currents. With a proprietary electrode structure, unique magnetic material, high saturation magnetic flux density, and optimization for high-frequency switching, it achieves low losses. The inductor ensures a withstand voltage of 100 VDC between the two coils.

Figure 1: Representation of TDK's VLBUC12060120R10LF3 dual coil power inductor for TVLR. Exact specifications should be obtained from the product data sheet. (Image source: TDK)

Measuring 12 mm by 6 mm with a height of 12 mm, the VLBUC12060120 series is available in versions with primary coil inductance ranges ‎‎from 70 nH to 200 nH, and saturation currents ranging from 58 A to 155 A. Their operating temperature range is -40°C to +125°C.

TDK utilized a circuit simulator to compare the change in output voltage during sudden load changes between an 8-phase multi-phase VR and a TLVR. The load voltage fluctuation in the multi-phase VR was ±0.3 V relative to 1.8 V, assuming a switching frequency of 800 kHz for a conversion from 12 V to 1.8 V, and using an output smoothing capacitor value of 1,850 μF for a load change of 240 A → 360 A → 240 A. In comparison, the output fluctuation in the TLVR was less than ±0.1 V, with significant reduction in time required for voltage stabilization. Additionally, the value of the output smoothing capacitor could be reduced to approximately 230 μF or about one-eighth of its original value.

Conclusion

The demands of data centers and cloud services for efficient server power management exceed the load responsiveness capabilities of traditional multi-phase voltage regulators. Utilizing TDK’s VLBUC series of dual coil power inductors in TLVR circuits can help product designers overcome the higher frequency challenges of increasingly dense processors, ensuring server power management can achieve the reliability required to process today's intense data-driven applications.