An Interleaved Dual-Battery Power Supply for Battery-Operated Electronics

Size: px

Start display at page:

Download "An Interleaved Dual-Battery Power Supply for Battery-Operated Electronics"

Harvey Carter
5 years ago
Views:

1 USC Low Power CAD An Interleaved Dual-Battery Power Supply for Battery-Operated Electronics Qing Wu, Qinru Qiu and Massoud Pedram Department of Electrical Engineering-Systems University of Southern California Los Angeles, California 90089, USA Massoud Pedram

2 Outline Introduction Background Analysis of Optimal Supply Voltage Design of Interleaved Dual-Battery Power Supply Conclusions

3 Batteries in Mobile/Portable Electronics Extending the battery service life for mobile electronics is a major motivation for low power design

4 Battery Power Supply System In reality, the battery discharge rate is super-linearly related to the average power consumption in the VLSI circuit DC/DC Converter Battery Discharge Rate (1/sec) VLSI Circuit Average Circuit Power (W)

5 Low Power Design Metrics Energy-delay (E-D) product [M. Horowitz, et al, 1994] Measures circuit speed for energy dissipation per operation Does not consider the characteristics of the battery power supply system Battery discharge-delay delay (BD-D) D) product [M. Pedram, et al, 1999] Measures circuit speed for battery discharge per operation Only considers the current-capacity capacity characteristics of the battery

6 In This Paper Further analysis of the BD-D D product Considers the current-voltage characteristics of the battery, in addition to its current-capacity capacity characteristics Design of an Interleaved Dual-Battery (IDB) power supply system Uses two batteries of different current-capacity capacity characteristics Calculates the optimal combination of the two battery types Increases the battery life time

7 Battery Characteristics Current-capacity Current-voltage

8 An Analytical Model Actual battery energy discharge E act V V I0 T =, 0 μ μ 0 Efficiency factor (current-capacity capacity relation) μ = 1 β I 0 Output voltage function (current-voltage relation) OC 0 = V γ I 0 Conversion efficiency equation (DC/DC converter) 1 η V0 I 0 = V dd I dd

9 Battery Discharge (BD) Definition BD = act E V0( I0) I0 T = CAP0 CAP0 μ( I0) Energy dissipation of the VLSI circuit V dd I dd T = 1 C sw V dd BD as a function of V dd and I 0 BD = 0 1 dd Csw V η CAP β I 0

10 Calculating the Battery Discharge Current Relation between V dd and I 0 ( OC 1 V I0 ) I0 T = C sw Vdd η γ I 0 as a function of V dd I 0 = η V OC η ( V OC ) η γ η γ C sw V dd T

11 BD-Delay (BD-D) Product Delay of CMOS circuits t d Vdd = m, 1 <. α ( V V ) dd th BD-D D product BD D = m Csw Vdd η CAP (1 β I ) ( V V ) 0 0 dd th 3 α

12 Determining the Cycle Time Assuming clock cycle time is proportional to circuit delay T V dd td T = m, 1 <. α ( V V ) dd Complete expression for battery discharge current th I 0 = η V OC η ( V OC ) η γ C η γ sw V dd ( V dd V th ) α m By substituting I 0 in the expression for BD-D, we can obtain a complicated expression for BD-D D in which V dd is the only variable.

13 An Example Assume a VLSI circuit consumes 13.5W power at supply voltage of 1.5V Parameter Value Comment V 0 η C sw m α V th 4V Typical lithium battery Typical DC/DC converter Calculated Typical CMOS technology Typical CMOS technology m C sw η CAP 0 1 Normalized β = {0, 0.05, 0.1, 0.15} γ = {0, 0.15, 0.3}

14 BD-D Curves BD-D product β=0.15, γ=0.3 β=0.1, γ=0.3 β=0.1, γ=0.15 β=0.1, γ=0 β=0.05, γ=0.3 β=0, γ=0 (ideal case) V dd (V)

15 Optimal V dd Values Optimal V dd (V) β γ

16 Batteries with Different Characteristics Battery A Battery B bobbin cell spiral cell

17 Block Diagram for the IDB Power Supply System Battery A Battery B DC/DC Converter VLSI Circuit Current Comparator I 0 I th

18 Design Problem Statement Given: Two batteries with different current-capacity capacity characteristics Current dissipation profile of the VLSI circuit A volume (or weight) limit (normalized to 1) for the power supply Divide the total battery volume (or weight) between these two battery types such that the t service life of the IDB power supply system is maximized

19 Analysis Setup Capacity (Battery efficiency μ) 1 x Battery A Battery B w 0 y 1 I p(i) 1 I 0 y II 1 I Battery Service Life (BSL) BSL = 1 act I ave

20 Single Battery Power Supply Using Battery A only BSL = w (1 (1 w) y ) Using Battery B only BSL = x

21 IDB Power Supply Optimal threshold current I th = y use Battery A use Battery B if if I I 0 0 < y y Optimal weight/volume distribution of the power supply z* = ( xy ) (1 y + xy ), 0 z* 1 Battery A occupies a portion of z* Battery B occupies a portion of (1-z*)

22 BSL as a Function of x, y and z BSL x=0.8 BSL y=0.8 x=0.7 y=0.7 x=0.6 x=0.5 y=0.6 y=0.5 z z (a) y is fixed at 0.5 (b) x is fixed at 0.5

23 BSL Improvement Plot BSL improvement x y

24 Conclusions It is important to consider the current-voltage characteristic of the battery in addition to its current-capacity capacity characteristic. By appropriately combining batteries with different current-capacity capacity characteristics (w.r.t. optimal portion of each battery type), the IDB power supply can significantly extend the battery service life.

Battery-Powered Digital CMOS Design

Battery-Powered Digital CMOS Design Massoud Pedram, Qing Wu Department of lectrical ngineering-systems University of Southern California, Los Angeles, California, USA {pedram, qwu}@usc.edu Abstr In this