mmax Power Management Chip Anthony Kanago Valerie Barry Benjamin Sprague John Sandmeyer 1
Outline Design Goals and Challenges Power Management IC Design Maximum Power Point Tracking (MPPT) Implementation Measurement Results Demonstration Platform Conclusion 2
Design Goals and Challenges Goals to design, fabricate, and test an integrated circuit (IC) to maximize the power production of an energy-harvesting system such as a micro solar cells, piezoelectric generator, or microbial bio fuel cells Challenges o Low-power operation o Low-voltage operation o Design complexity o Size limitation 3
Why Maximum Power Point Tracking? Maximum power point tracking (MPPT) is critical for efficient power generation from photovoltaic (PV) sources. Harvesting energy from small or integrated solar cells requires a lowpower MPP tracker and power management system. Electrical Model of PV Cell 4
Fractional Open Circuit Voltage The ratio of open circuit voltage (V OC ) and maximum power point (MPP) voltage (V mp ) is constant for fixed operating point. This is true for photovoltaic (solar) cells, thermoelectric generators (TEG) and microbial fuel cells (MFC). V mp 550mV Fraction=0.55 Micro Solar Cells V Thermoelectric Generator Microbial Fuel Cells oc 5
Fractional MPPT Implementation 0.4MΩ 1.6MΩ 200nA Utilize a pilot cell Approximate Voc with very large R string Comparator speed, input range considered 6
System Overview 7
Circuit Implementations
Fractional MPPT 9
Fractional MPPT V solar V oc V mp 10
Fractional MPPT V solar V oc V mp Trade off smoothing of Vsolar for response time with low-pass filtering 11
DC-DC Conversion 0-V AA V thp + V AA Clock self-generated by MPPT Comparator 12
Charge-Skimming Regulator (CSR) Structure imitates Anti-Blooming control in CCD/CMOS Imagers V target - V thp 13
Charge-Skimming Regulator (CSR) Structure imitates Anti-Blooming control in CCD/CMOS Imagers 1.8V 1.2V V target - V thp 14
Simulation Results Total Power Consumption: 17 mw Block Component Power Consumption Maximum Power Point Reference Generator Power Management TOTAL POWER Comparator Divider Beta Multiplier Reference Current Digital to Analog Converter Two Comparators Dynamic Power 1.56 mw 1.56 mw 0 mw 4.74 mw 3.13 mw 1.61 mw 10.72 mw 3.12 mw 7.60 mw 17.02mW 15
Results Circuit Area 0.35mm2 Measured Power Consumptions During Harvesting -17.54μW After Caps Charged 18.04μW 16
Measurement Results Vout2 1 2 3 1.2V 1.8V 6x SCPD Devices @ 30K Lux Vout 2x 1000mF Caps (1) V out1 charged (1.8V) (2) V out2 charged (1.2), self-powering (3) CSR engages Vout2 1 2 3 PWR_Self 1.2V 1.2V 17
Demonstration Platform Sample state of system realtime using ADC Send via USB to host PC (Windows) Host PC plots signals realtime Custom wireless display interface using Android Tablet 18
Demonstration Platform Sample state of system realtime using ADC read by Xilinx FPGA Send via USB to host PC (Windows) Host PC plots signals realtime Custom wireless display interface using Android Tablet 19
Demonstration Platform 20
Summary Fractional open-circuit voltage MPPT Integrated, self-clocked, boost converter for voltage step up A new charge skimming regulation (CSR) suitable for low-voltage, lowpower applications Low-overhead power management algorithm 21
Acknowledgement Thank you to Dr. Ay and VSRG for opportunity, facilities, fabrication! Cadence University Program MOSIS Educational Service 22
Q & A 23
Testbench 24
Solar Cell Data Illumination (lux) 1000 10000 30000 Voltage at Max Power (V) 0.2795 0.342 0.378 Current at Max Power (A) 0.000015573 0.000111 0.000342 Short Circuit Current (A) 1.76621E-05 0.000129 0.000403 Open Circuit Voltage (V) 0.3581 0.439 0.487 Rso (Ohms) 2540.8 408.58 186.359 Rsho (Ohms) 932000 555082 22145 Rsh (Ohms) 932000 555082 22145 n 1.102979687 1.766947 1.402414 Is (Amps) 6.21512E-11 8.78E-09 5.73E-10 Rs (Ohms) 887.403505 52.97767 91.10892 Iph (Amps) 1.7679E-05 0.000129 0.000405 25
Solar Cells Series vs. Parallel 26
Power Management Switch Layout 27
MPP Comparator Layout 28
MPP Divider Layout 29
Power Management Switch Layout 30
Current DAC Layout 31
Top-Level Simulation 32
Top-Level Simulation 33
Current Digital to Analog Converter (idac) Schematic Design 34
BMR Simulations Transient Analysis DC Voltage Analysis 35
MPP Divider Simulation Transient Analysis 36
Battery Operation 37