Inductor Multipliers for DC-DC Converters

Transcription

1 Inductor Multipliers for DC-DC Converters ditya Makharia dvisor: Prof. Gabriel incón-mora Georgia Tech nalog Consortium School of Electrical and Computer Engineering Georgia Institute of Technology, tlanta, US October 31, 2003

2 Introduction Mobile, battery-powered applications require:» Low Voltage, High Efficiency, High Power, High ccuracy solutions.» SOC Integrated Power Supply circuits (dc-dc) Integrated Power Inductors State-of-the-art:» External inductor Take-up PCB eal Estate dd Cost» Integrated inductor Low-Power pplications Low Efficiency» MEMS inductor Compatible with most fabrication processes Low quality (Q) factor.» Charge Pumps No Inductors are needed Very low power applications» Linear egulators Poor efficiency Low power applications Goal:» Integrate Power Inductors onto the die/package and multiply the effects of a small integrated inductor using Inductor Multipliers). WHY N INDUCTO? V IN V ph L C OUT I O V OUT Makes efficient energy transfer to load. Digital Signal at V ph ; LC filters it to V OUT L determines output current ripple ( I L ), voltage ripple ( V OUT ), and bandwidth. Error mplifier and Switch Control s L I L Power, V O_ipple ccuracy

3 Proposed pproach - Inductor Multiplier Operation:» The voltage across the inductor is constant therefore to enhance the value of inductor, current is increased. di di di V = L = L(K ) K L Leff = K L dt dt dt Implementation:» Use a current-controlled-current-source to sense the ripple current through the inductor, and subtract a portion of it from the node. (K-1)/K I ON_CHIP (K-1)/K I ON_CHIP L EFF I ± I LEFF B L ONCHIP L ONCHIP B B I L_ON_CHIP = K X I LEFF L EFF = K X L ON_CHIP I ± I L_ON_CHIP I ± I L_ON_CHIP Issue:» The potential at node is greater than B, hence the flow of current is not realizable. Solution:» Since is a low-impedence node, take the current to ground. Trade off:» Increased losses and hence reduced efficiency.

4 Proposed pproach - Inductor Multiplier Buck-converter with the inductor multiplier. Current waveforms of the inductor multiplier in a buck-converter. IIN VIN (K-1) ILEFF LON_CHIP I O ± I L_ON-CHIP ILEFF Error mplifier & Switch Control IO COUT ES VO CUENT VOLTGE 0 I VG = I OUT ton τ toff I LEFF I L_ON_CHIP CLOCK INDUCTO CUENT CPCITO CUENT For times t1 &t3, I L <I OUT ; Inductor multiplier sources the required current. 0 t1 Sourcing Current t3 (K-1) I LEFF INDUCTO MULTIPLIE CUENT For t2, I L > I OUT ; Inductor multiplier sinks the extra current. Sinking Current t1 + t3 =t2= 2 τ t2 TIME

5 Proposed pproach Implementation Ideal implementation: Sense the current accurately and amplify it. Cons: ccurate current sensing techniques are either lossy or complex. Proposed implementation:» In a buck converter: VOUT = VC + VES + VESL VES = I C ES I C : capacitor ripple current I L For electrolytic capacitors, the voltage ripple is ES dominant. V DD V EF L C OUT ES I O I C V O G m V EF I IM = G m (V EF -V O ) V O 1 2 V EF 1 : n M P 1 2 If V O > V EF, G m sinks current If V O < V EF, G m sources current K -1 G m = (K: multiplication factor) ES G m = 2 1 n ccurate G m Low I Q Bandwidth Limited V EF 1 : n M N

6 Proposed pproach Implementation Prototype Implementation of Inductor Multiplier L I O V O V S+ V EF V S- 1 2 V EF V DD 1 : 1 M P G m = = 80 2 f CL = = 10*f SW 1 V IN C OUT ES I C I LOD 1 2 = 1Ω, to obtain large G m since mirror ratio n=1 EVM Switch Control V EF V S+ V S- 1 : 1 M N For the integrated version n~1000, ~20Ω and GBW~10MHz EVM-TPS54610 V IN : 5V V O : 2.5V I LOD : 0-6 f sw : 550 khz L=1.2uH ES in the EVM is ~15-20 mohms. Inductor-Multiplier (M=2.7) V DD : 5.0V V EF : 2.5V : 1Ω 1 :100Ω, 2 : 8kΩ High-Speed mplifier (THS 4271) Gain Bandwidth ~ 500MHz V S ± = ± 6.0V Matched Transistors M N : NDS9945 ( Imax =3) M P : NDS9948 ( Imax=3)

7 Simulation esults Simulation esults of the Prototype Efficiency Vs Load Current - Comparison P Efficiency(%) Q L=1.5uH L=150nH (with Ind. Multiplier) V IN = 5V, V O = 2.5V, I O = 2.5 ES =15mΩ L=1.2uH multiplied to 3.3uH ILoad (mps) Onset of negative I L at P and Q. Peak Efficiency (η) = I LOD = 2.5 and Multiplication factor=10. (η = 70% for Linear egulators).

8 Conclusions & Future Work Charge Pumps External Inductor Linear egulators MEMS pproach Inductor Multiplier SOC Feasibility Worst Worst Best Good Best Output Power Low High Low Moderate Moderate Cost (Process Tech.) High Highest Low High Low Efficiency Good Best Worst Poor Moderate Complexity Good Good Best Poor Poor Conclusion Inductor multiplier SOC/SOP Solution medium power portable applications. Provides better efficiency than the linear regulator. Future Work: Investigation of techniques for the integration of the inductor. Evaluate the performance of the prototype and move towards integrated solution.