The efficiency of a Point-of-Load converter is a decreasing function of its input voltage. If the prior stage bus converter can achieve a higher conversion ratio without much extra loss, the input voltage of the PoL converter can be decreased, and the overall 48V-to-PoL efficiency can be improved.

Peak power stage efficiency 98.6%Peak system efficiency

(including gate drive loss)98.0%

Full load efficiency 96.0%Power density 1675 W/in3

48-to-6 V performance summary Full load with fan cooling only

Zichao Ye, Wen Chuen Liu Rose Abramson, Robert Pilawa-Podgurski

Hybrid Resonant Switched-Capacitor Converters: Achieving Ultra-Efficient and Compact High-Step-Down DC-DC Power Conversion for Datacenters

IntroductionThis work presents a family of high-performance hybrid resonant switched-capacitor (SC) power converters for datacenter power delivery, from 48 Vdc to an intermediate bus voltage (12, 8, 6 or 4 Vdc). This technology can achieve significantly higher efficiency and power density than the current state-of-the-art and has the potential to greatly reduce the power distribution loss in future datacenters.

Why Hybrid Switched-Capacitor Converters

C1

S1

C2

Resr

Vin

S1A

S1B

L

+Vout

_Co

Vx

S1a S2a

S1b S2b

C1VinRloadCo

Hybrid switched-capacitor converters use both capacitors and inductors in the power transfer process. The inductor behaves like a current source and can help recover the charge sharing loss, through soft charging operation.

Capacitors have an energy density that is up to 1000x higher than inductors. However, their inherent charge sharing loss significantly undermines this advantage.

Dimensions: 1.38 x 0.46 x 0.22 inch (3.5 x 1.17 x 0.55 cm)

Focus of this work

Moving Towards A Lower Bus Voltage

48-to-6 V Multi-Resonant-Doubler Converter 48-to-4 V Two-stage Resonant Converter

8-to-1 Ratio Switch number

Capacitor number

Inductor number

This work 10 3 1Fibonacci 13 4 1

FCML 16 7 1Series-Parallel 22 7 1Switched Tank 22 7 3

This design features the least possible number of components among all SC topologies for a conversion ratio of 8:1.

Switch rating: 12Vin,

14Vin,

18Vin

Capacitor rating: 12Vin,

14Vin,

18Vin

10 A to 40 A load step

Switching waveform

Measured 48-to-6 V efficiency

VT LLC [1]

Google STC [2]4-to-1 ratio

EPC Buck [3]GaN FET

This workComparison with existing state-of-the-art

This design features the lowest passive volume requirement while maintaining high output conductance.

Co Ro

Vout

C3 C2 C1

Lo2

C5 C4

Q5pb

Q5pt Q4pt Q3pt Q2pt Q1pt

Q4pb Q3pb Q2pb Q1pb

Q5s Q4s Q3s Q2s Q1sQ6s

Vsw

ILVin

C6

Q1A

Q2A

Stage I 2-to-1 ReSC

Stage II 6-to-1 Series-Parallel Switched ReSC Converter

Co1

Lo1

Q2B

Q1B

VmidVsw1

IL

Vsw

ΔVc6

0

0

–Vd

Io / 6

Tsw1

Q1A, Q2B

Q2A, Q1B

D1Tsw1

ϕ1 ϕ2

ϕS ϕP

D2Tsw2

IL

VswΔVc

5ΔVc

0

0

–Vd

Io

Tsw2

ϕS ϕP

C5 C4 C3 C2 C1 25 V MOSFET 23 nH

UCC 27211 23nH

C6 40 V MOSFET 180 nH

UCC 27211 Cmid2

Top

Side

Bot

tom

Sid

e

Cmid1

IL

Vsw

ϕs

ϕp

No Products Available

GV Dominant

GV2 Dominant

Measured 48-to-4 V efficiency

FoM: Output Conductance x Density

0805 SMD MLCC

Discrete Si Transistors

94%

91%

88%

5V 8V 12VVin

1 V PoL converter efficiency with respect to Vin

*Based on Murata MYMGK00504ERSR, MYMGK1R804FRSR

However, the component number of SC-based bus converters increases proportionally with respect to the conversion ratio, resulting in increased circuit complexity and decreased performance. To address this challenge and continue the promise of SC technologies, we developed two new Resonant SC topologies that are specifically suitable for high conversion ratios (48-to-6 V and 48-to-4 V).

12 V – 4 V

Peak power stage efficiency 98.3%Peak system efficiency

(including gate drive loss)97.0%

Full load efficiency 93.6%Power density 1154 W/in3

48-to-4 V performance summary

Full load with fan cooling only

Switching waveform

{yezichao, joseph.wcliu, rose_abramson, pilawa}@berkeley.edu