Audio, video chips enhance handheld devices’ features, shrink power needs
By Margery Conner, Technical Editor -- EDN, June 28, 2007
A handheld consumer device’s display and audio are often the features that determine the product’s success or failure. However, audio and video bells and whistles can also destroy a battery-operated device’s power budget. So, you should spend some design serious time selecting and designing audio and display capabilities for your next handheld product. To help you with those designs, National Semiconductor has introduced a suite of display, audio, and power-management ICs that conserve space and power in handheld multimedia-enabled devices, and they streamline the design of these features.
For example, you may assume that the most efficient way to backlight a handheld display is with a white LED, but this approach isn’t necessarily the best choice for today’s high-definition, full-color handheld displays. Mark Davidson, marketing director for the power-management division for National Semiconductor, points out that so-called white LEDs vary in their whiteness, which changes over time. If you lock yourself into a single, fixed-color white LED for illumination, you thus give up the ability to compensate for LED aging, as well as variability in display color. National’s new LP5520 RGB LED driver, which sells for 90 cents to $1.85 (1000), tunes three RGB LEDs to produce a true white light over a wide temperature range without the need for optical feedback. But you still must allow for individual screen and LED characteristics: For example, you might need to use various vendors’ LEDs and screens, all with different aging characteristics. So, National also offers the $3.40 (1000) FPD95120 LTPS (low-temperature-polycrystalline-silicon) display driver, which includes an EEPROM. You can use the driver with multiple manufacturers’ displays because the EEPROM stores module-calibration data to match color and flicker parameters and the ability to program unique product identification.
Video processing represents another significant portion of a device’s power budget. The LP5552 power-management IC supports AVS (adaptive voltage scaling) to enable processors that incorporate National’s PowerWise intellectual property to adaptively adjust the supply voltage to the minimum necessary level. Available in a 36-bump micro-SMD package, the $4.50 (1000) LP5552 includes two 800-mA buck regulators and five LDO (low-dropout) regulators).
Audio quality is just as important as video in defining a device’s quality. The LM49100 audio chip routes monophonic-voice or stereo-music signals to a mono-speaker driver or stereo ground-referenced headphone amplifiers through preset modes. It also provides layout flexibility through its headphone’s ground-sensing function. To maximize battery life, the $3.35 (1000) LM49100 has a quiescent current of less than 5 mA with all channels active.
