15Analog Applications Journal - PDF document

15Analog Applications Journal challenge for powering this type of load. To decrease theas close as possible to the microprocessor. µP OR DSPwith HF decouplingorESRLO1-DDVINDriverDriverLnChannels2 ... (n-1)Q During Transient D 1-D +Ð Q Q Die Figure 1. Model of interleaved synchronous buck converter to be analyzedContinued on next page Texas Instruments Incorporated 16Analog Applications Journal turn the high-side FETs on at load-equivalent one-channel converter.Assume that 1– D nD, where nvoltage below 2 V. For example, the popular 12-V-input and1.6-V-output synchronous buck converter with four channelsis the switching frequency, tis the output inductor, Vis the peak-to-peak inductor-converter. Deqv, feqv, teqv, Leqv, Veqv, and are, respectively, the duty cycle, switching frequency,switching period, output inductor, input voltage, and peak-to-peak inductor-current ripple of a one-channel, equivalent buck converter. Because all channels turn toleaved converter. The interleaving gives the same effect asoutput filter characteristics, including the inductor-current I: Ch. 1 + Ch. 2I: Ch. 1 + Ch. 2 D x ts (1-D) x tsts teq(1-Deqv)xteq Deqvxteq IL ILeq Figure 2. ÒIdealÓ control algorithm for best transient responseContinued from previous page Texas Instruments Incorporated 17Analog Applications Journal . For the step-up transient, however, whenall the high-side switches are turned on, the inductor--(IN – VOUT) x n]/LO, which is muchhigher than in steady-state operation during the Deqv partof the switching cycle, where the slew rate is only (VIN – VOUTx n)/LO.Optimal output filter selectionTypical waveforms during the load-current step-downon the controller, because usually the controller’s transientapplies to the interleaved converter. The only difference isanalysis) to the equivalent one-channel converter. ForVreq and Vm2 = Vreq, respectively, aseqv, and number of interleaved channels n: CfnESRESRCfnCfn211Š++×××××× \t\tCfnKLVreq ESLESRESRtfn Vreq, and Vm1Vm2 ISummarizedOutput Voltage Figure 3. Typical waveforms during where KL = ILeqv/IOor(3)(4)Parameter m depends on the type of transient:m = 1 – nD(5)for the worst-case step-down transient, and(6)for the worst-case step-up transient. DnD VDnLeqvIfnOUTOOs××× the converter has to be located closer to a microprocessor, fnKLESRCtŠ× Continued on next page Texas Instruments Incorporated 18Analog Applications Journal PARAMETERS OFTYPEVENDORPART NUMBEREACH CAPACITORNUMBER OF CAPACITORS FOR DIFFERENT NUMBERS1ESR1ESL1OF INTERLEAVED CHANNELS/L(µF)(m)(nH)1 CHANNEL2 CHANNELS3 CHANNELS4 CHANNELS Aluminum electrolyticRubycon6.3ZA10002001000244.818/0.8 µH16/1.6 µH16/2.4 µH15/3.2 µH OS-CONSanyo4SP820M20082084.88/0.25 µH7/0.5 µH6/0.75 µH6/1.0 µH Specialty polymer (SP)PanasonicEEFCD0D101R300100203.228/0.1 µH18/0.2 µH15/0.3 µH13/0.4 µH Ceramic, 1210MurataGRM235Y5V226Z1040022200.560/0.05 µH30/0.1 µH20/0.15 µH16/0.2 µH Table 1. Comparison of capacitor types To illustrate the theoretical analysis, different types ofpolymer, and ceramic) are compared in Table 1.= 12 V, V= 1.5 V, IVreq = 100 mV, SReqv (Figures 4-7). Tointerleaved converter, the equivalent inductance needs totor, the number of capacitors N1 related to the peak Vm1“ideal” controller, assuming that it has equal current shar-ing, the optimal control algorithm described earlier, and noTable 1 shows the required number of capacitors N2 and 0.50.60.70.80.911.11.21.31.41.5 Equivalent Inductance Leqv (H). L= n x Leqv Curves N11 ch.Curves N21 ch.4 ch.Number of Capacitors (N1 and N2) Figure 4. Number of aluminum electrolyticcapacitors as function of LOeqv 0.10.20.30.40.50.60.70.80.911.1 Equivalent Inductance Leqv (H). L= n x Leqv.= 200 kHz/channel Figure 5. Number of OS-CON capacitors asfunction of LOeqvContinued from previous page Texas Instruments Incorporated 19Analog Applications Journal February 2001Analog and Mixed-Signal Products Number of Capacitors (N1 and N2) Curves N21 ch.Curves N11 ch. 0.050.0750.10.130.150.170.20.220.250.270.3 Equivalent Inductance Leqv (H). L= n x Leqv.= 300 kHz/channel Figure 6. Number of SP capacitors asfunction of LOeqv Table 1. The output inductance of each channel is 0.2 µH.Power-supply systems for high-slew-rate transient loadson practicality and sufficient accuracy, includes an inter-power-supply plane parasitics. Analytical equations for theelectrolytic, OS-CON, SP, and ceramic capacitors for pow-ering a 50-A microprocessor with an interleaved regulator.1.International Technology Roadmap for Semiconductors,2.Y. Panov and M.M. Jovanovic, “Design Considerationsfor 12-V/1.5-V, 50-A Voltage Regulator Modules,” 3.“Investigation of Power Management Issues for NextElectronics Systems (Virginia Tech, September 1999).4.Bau-Hung Lin and Ying-Yu Tzou, “Analysis and Designof a Multiphase DC/DC Converter with Zero VoltageTransition,” 5.W. Huang and J. Clarkin, “Analysis and Design of Multi-6.R. Miftakhutdinov, “Analysis of Synchronous BuckLoad Current Transients,” 7.R. Miftakhutdinov, “Analysis and Optimization ofCurrent Transients,” loadan Acrobat Reader file at www-s.ti.com/sc/techlit/Document TitleTI Lit. #8.R. Miftakhutdinov, “Optimal Output Filter Supply,” (August 2000), pp. 22-29 . . . . . . . . . . . . . . . . . . .slyt162Related Web siteshttp://power.ti.com Figure 8. Step-down transient for 2-channelconverter with 18 SP capacitors in parallel Number of Capacitors (N1 and N2) 0.030.040.050.060.070.080.090.10.110.120.13 Equivalent Inductance Leqv (H). L= n x Leqv.= 400 kHz/channel Number of Capacitors (N1 and N2) 0.030.040.050.060.070.080.090.10.110.120.13 Equivalent Inductance Leqv (H). L= n x Leqv.= 400 kHz/channel 012345ISummarizedF, 2 VOutput Voltage6789101112131415 Time (microseconds)V(20 mV /div), Iand I(10 A/div) IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reservestandard warranty. Testing and other quality control techniques areused to the extent TI deems necessary to support this warranty.applications using TI components. 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