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Analog ICs aid low-power handset designs

Posted: 27 Jun 2007 ?? ?Print Version ?Bookmark and Share

Keywords:data serialization? RGB LED driver? analog ICs? RF power amplifier?

In handheld, multimedia designs, where power is precious, a good designer needs to do more than simply select the lowest-power components that will do the job, as demonstrated by a cluster of new, analog-centric, components from National Semiconductor. In addition to low power itself, these components help designers implement the low-power tactics essential to longer operating times.

The LM2512 Mobile Pixel Link (MPL) performs data serialization of video data, as part of the processor-to-display bridge, reducing 24 signals to 3 or 4 active signals. It includes a look-up table for color correction to match different displays. To further conserve power, it can dither data from lower-power, 6bit RGB data converters (18bits total) to yield 8bit appearance (24bits).

The FPD05120 multifunction display driver includes an MPL deserializer, inductive DC/DC switching supply, RAM and personalization EEPROM. What's especially interesting about this part is its packaging (or lack) and how it is mounted in the final system: the almost-transparent, low-temperature polycrystalline silicon device is 0.9mm wide and is attached onto the top of the display glass, at its edge, to minimize use of usable display area.

The LP5520 RGB LED driver allows the use of red, green and blue LEDs to provide white backlighting for the display. With individual calibration coefficients for each color and without optical feedback, these drivers and the LEDs produce a truer white light, with a color gamut approaching 100 percent of the NTSC standard (compared to a typical 70 percent). The IC includes provision for a temperature sensor to compensate for temperature-induced LED-output variations. There is also an adaptive mode where the driver automatically adjusts the output voltage for the lowest possible power consumption.

On the audio side, which National says tests show actually contributes to perceived video quality by the user, the LM49100 Audio Subsystem can route mono voice or stereo music signals to a mono speaker driver or to stereo ground-referenced headphone amplifiers (or both) through simple selection of pre-set modes. It also provides layout flexibility through its headphone ground-sensing function. Quiescent current is less than 5mA, with all channels active.

A cluster of new, analog-centric, components from National Semiconductor can help designers implement the low-power tactics essential to longer operating times.

For power management, the LP5552 energy management unit operates at 3.5MHz, with two 800mA buck regulators (180 out of phase) to reduce net EMI, plus five low-dropout regulators (LDOs). It is PWI 2.0 open-standard compliant, with digitally controlled intelligent voltage scaling and automatic or pulse-width controlled transitioning between pulse-frequency mode (PFM) transition, to minimize power consumption. For CDMA operation, the LP3919 power management unit includes switching regulators, LDOs, a battery charger and overvoltage protection.

For the microdrives which are increasingly incorporated into handheld multimedia units, the LM3668 buck-boost regulator is optimized for operation from a Li-ion source between 2.5- and 5.5V, with seamless, bumpless transitioning between buck and boost modes, output voltages of 2.8-3.3V at 1A and better than 90 percent efficiency. The 2.2MHz, single-inductor design also includes a pair of N-channel and a pair of P-channel MOSFETs. If you use instead use high-capacity mini SD/SD memory, LP3929 provides the requisite logic-level shifting, ESD protection and EMI filtering as well as an ultralow-dropout CMOS voltage regulator. The level shifter bridges the 1.8V LVCMOS host side with the 2.85V LVCMOS levels on the card side.

Finally, for the RF power amplifier, the LM3207 step-down DC/DC converter also integrates a voltage-reference LDO. This IC operates from a single Li-ion cell at 2MHZ, with a variable, analog-controllable output voltage of 0.8-3.6V and 650mA maximum load capacity. Efficiency is in the 95 percent region.

- Bill Schweber
Planet Analog

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