Give Your Battery A Rest With A Supercapacitor-based Power Subsystem
by Greg Lubarsky, National Semiconductor, Santa Clara, Calif., How2Power Today, Nov 24 2009
Focus:
Handsets are becoming more feature rich and power hungry with the adoption of high-current LED flashes, high-power stereo drivers, and multiple RF power amps. Unfortunately, each of these functions can draw large pulses of battery current when in use. If allowed to operate at the same time, these features can cause a battery current fault or shutdown of the device. Possible fixes include pulse timing management and performance compromises such as limiting the flash current or audio volume, both these approaches limit the phone's capabilities. This article describes an alternative solution that extends the battery's performance by adding a supercapacitor and a supercapacitor management IC (the LM3550). The article provides some background on supercaps (EDLCs) and their capacitance and voltage specifications, discusses placement of a supercap in a battery-powered device and how it supports the battery in supplying pulses of current to the load, and the influence of battery ESR and supercap ESR on supply voltage droop. The functional requirements for a supercap management IC are described and performance results are shown for an LM3550 plus 0.5-F supercap combination in an example application.
What you’ll learn:
- How to understand the advantages of using a supercap to support the battery in supplying peak currents in feature-rich mobile handsets
- How to understand charge management and circuit protection requirements when using supercaps to support battery-powered operation
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