We've come a long way since the seven transistor walkie-talkies and AM radios of my youth. Single function devices are no longer the norm; today's portable electronics are "feature-rich." The wristwatch is also a TV remote control; a cell phone is a camera and a calculator; a MP3 player is a radio, mobile memory storage device, and photo album; the PDA is a calendar, camera, cell phone, and a hand held game; and the list goes on. At times it can be difficult remembering what the primary function of these devices really is. As we add more and more functionality to our portable electronics a greater burden is placed upon the power source.
We can't be expected to drag around a car battery to power all these additional functions, and even the days of AA, AAA, and 9-V batteries are numbered. The battery of choice for today's electronics is the lithium-ion rechargeable battery. They offer quick recharge times while delivering hours of operating time and weeks of standby time. Power management and battery supervisory circuits have spawned new product families, whose sole purpose is efficiently managing the power source to extend operating time. Advances in power management and battery technology have helped extend battery life, but its only part of the equation. The real trick is making the integrated circuit (IC) more efficient, the ability to do more with less. Today's IC's are required to operate on lower voltages, provide wider bandwidths, faster switching, more bytes, less distortion, and do all this using less current than previous generations of IC's.
Video is now becoming a feature found commonly in many of today's portable electronics devices such as personal media players and cell phones. The size and resolution of handheld displays limits their ability to share images with large groups, however, so video outputs are required. This new feature, however, represents yet another drain on the battery. Video outputs on such devices are typically auxiliary functions; therefore, the video driver is typically off during normal operation. For this reason both operating- and standby-current are critical parameters, to be addressed when designing in the additional video circuitry
For a more insightful look at the challenges faced by today's engineers regarding standby, operating and quiescent current, two design examples are presented. In the first example, the design requirements for a MP3 player video output section are discussed. In this example the primary design consideration is operating current and board area. The second example deals with very low power buffer application where standby current is the main concern.