Energy efficiency is a key design consideration in a National Semiconductor line of ICs intended for batterypowered phone and video systems. Minimizing power consumption is the common thread in these circuits, which convert digital data into real-world video playback subsystems (see the figure). This involves efficient power sources plus digital techniques that minimize power dissipation using analog, digital, and mixed-signal technology ICs.
Application processors for video systems consume substantial energy, which limits battery life. To minimize these requirements, National’s PowerWise technology uses adaptive voltage scaling (AVS). Integrated onto these processors along with compatible power-management ICs like the LP5552, AVS reduces energy consumption by up to 70%, extending battery life.
With AVS, these processors can adaptively adjust its supply voltage to the minimum level needed, greatly reducing its energy consumption. The LP5552 includes two 800-mA buck regulators and five low-dropout regulators (LDOs).
For powering baseband functions, there’s the LP3919 power-management IC, which features high-efficiency switching regulators, LDOs, and a battery charger. It powers the baseband processor as well as other system circuitry.
ENHANCING THE DISPLAY
National’s low-power Mobile Pixel Link (MPL) family streams large quantities of data (seen as video and graphic images) to an LCD while maximizing battery life. The MPL device serializes the data to reduce the wire count, which decreases the size of the connector and flexible pc board. MPL reduces electromagnetic interference (EMI), and its power consumption is roughly half that of similar products. In addition, MPL handles the voltage-level translation between the host and the display, eliminating the need for an external level shifter.
The newest MPL, the highspeed LM2512 serial host device, supports a video-mode interface bridge between the processor and the display. It’s highly programmable, with a built-in lookup table that allows color correction, so designers can optimize video viewing. The LM2512 also includes a dithering function, allowing 24-bit video to be displayed with high quality on 18-bit displays, preserving the lower power consumption associated with 6- bit RGB (red-greenblue) data converters.
The FPD95120, a highly integrated, high-performance, low-temperature polycrystalline silicon (LTPS) display driver, is the narrowest glass-mounted device available for half- VGA format. Its 0.9-mm width maximizes display glass active area. Also, it provides an MPL deserializer, a high-efficiency inductive dc-dc switcher, and RAM to enable standby, low-power display capabilities.
BACKLIGHTING AND COLOR
Compared to white LEDs, RGB LED drivers provide better colors on the display and lower power consumption. The LP5520 offers a small and simple solution without the need for optical feedback, producing a true white light over a wide temperature range while improving the color gamut from 70% up to 100% of the NTSC standard. In the adaptive mode, driver circuitry automatically adjusts the output voltage for the lowest possible power consumption.
The LP5521, LP5522, and LP55281 color-management chips feature lowpower color LED drivers for handheld lighting applications. The digital core processes data received from nonvolatile storage, such as a secure digital card, flash, or a micro hard drive. Each of these sources presents a unique energy-consumption challenge in handheld devices.
To power a micro hard drive, the LM3668 buck-boost regulator provides a 3.3-V output voltage to power the driver motor. It offers greater than 90% efficiency in buck and boost modes, which is essential for driving high-power applications. The lithium-ion battery in handheld devices discharges from levels above 3.3 V to below 3.3 V.
Sending data wirelessly consumes significant battery power. The LM3207 dcdc power supply, optimized for 3G RF power amplifiers, dynamically reduces the power amplifier’s energy consumption by tightly regulating the RF power amplifier supply voltage to the lowest possible level while maintaining poweramplifier linearity.