Toshiba Launches Charge Pump White LED Driver With Constant Current Regulator

Apr 22, 2005

Toshiba America Electronic Components, Inc. (TAEC)* today announced a new charge pump DC/DC converter IC that drives the white light-emitting diodes (LEDs) used to backlight liquid-crystal display (LCD) panels and illuminate keypads in portable devices such as cell phones, PDAs, MP3 players and digital cameras. Specially designed for constant current driving, TCA62735FLG can drive up to four white LEDs with uniform brightness. Mass production is scheduled to start this month with a monthly production volume of three million units.

“A wide range of portable applications from cell phones to MP3 players increasingly use white LEDs for LCD panel backlighting and keypad illumination. In response, Toshiba Corporation engineered the TCA62735FLG white LED driver to provide an efficient solution in electrical performance with constant current output for up to four white LEDs,” said Andrew Burt, director of the Wireless Business Unit at TAEC. “The optimized design minimizes total circuit size, contributing to the portable equipment’s small form factor.”

The TCA62735FLG incorporates a power circuit and 4-channel fixed current output in a single chip and can drive fixed current to a total of four white LEDs, one for each output. It has a total output current capacity of greater than 120 milliamperes (mA) across all four channels. It achieves high-precision current regulation of 2.5 percent between the four channels and all four white LEDs attain identical brightness. Since TCA62735FLG monitors the power supply voltage and output pin voltage, it automatically switches the optimum step-up scaling factor in the LED load from 1.5 times to 2 times. Toshiba designed this device to minimize the efficiency degradation resulting from power supply voltage fluctuations, which was a weakness of older generation charge pump DC/DC converters. The switching frequency of 1 megahertz (MHz) makes it possible to select a small external component. The TCA62735FLG is housed in a space-saving 4mm x 4mm standard QFN16 package.

Main Features

-- Has an output current capacity that supports power supply voltage of 2.8 to 5.5 volts (V) and can provide more than 120mA to a total of four channels
-- Features on-chip fixed current output with standard current precision of 2.5 percent between outputs; configurable with a single external resistor
-- Provides a built-in, over-output voltage protection circuit
-- Provides a built-in soft start function
-- Has shutdown consumption current of 1 microampere maximum (rated 0 typical)
-- Achieves power-efficiency of 70 percent or greater (rated at a power supply voltage of 3.6V, output current of 120mA and white LED forward voltage of 3.6V)
-- Achieves power-efficiency of 90 percent or greater (rated at a power supply voltage of 3.6V, output current of 80mA and white LED forward voltage of 3.2V)

Development Background

Previous product generations of charge pump type DC/DC converters that only output voltage were characterized by wildly changing LED current values due to fluctuating white LED forward voltage drop (Vf). As well, these devices had difficulty achieving uniform brightness. When the relative ratio between the output voltage and white LED Vf was not suitable, reduced efficiency resulted. By employing a constant current driver, this new product can provide uniform brightness across all four LEDs. Since it automatically switches the optimum step-up scaling factor, it can attain high efficiency in lighting the white LEDs.

Samples are currently available and volume production is scheduled to begin this month. Pricing is $0.96 each in 1,000-piece quantities. An evaluation kit to speed designs is also available.

Explore further: Greenland darkening to continue, predicts CCNY expert Marco Tedesco

Related Stories

China's struggle for water security

33 minutes ago

Way back in 1999, before he became China's prime minister, Wen Jiabao warned that water scarcity posed one of the greatest threats to the "survival of the nation".

Canada revises upward CO2 emission data since 1990

43 minutes ago

Canada revised its greenhouse gas emission data from 1990 to 2013 in a report Friday, showing it had higher carbon dioxide discharges each year, and a doubling of emissions from its oil sands.

Recommended for you

Bloomberg blames 'internal network issue' for global outage

14 hours ago

Bloomberg LP's trading terminals, which are used by most of the world's biggest financial firms, went down for a few hours Friday due to apparent technical problems, a crash that prompted the British government to postpone ...

Taiwan factory workers win $18 mn over cancer deaths

17 hours ago

Workers from a factory in Taiwan which leeched toxic chemicals they say resulted in 200 deaths from cancer and more than 1,000 other cases of the disease won a Tw$564.45 million ($18 million) payout from US electronics company ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.