Duo of Tiny Devices Features High-Voltage Boost Converters, Programmable Constant-Current Drivers.
National Semiconductor introduced two new, highly integrated lighting management units (LMUs) that include a high-voltage boost converter and programmable constant-current driver to control up to 20 series-connected LEDs in display backlights, and keypad, RGB and camera flash LEDs. The LP3958 and LP5526 LMUs feature tiny micro SMD packages and are well-suited for cell phones and other handheld devices.
National’s new LMUs drive from two to five strings of four series-connected LEDs, depending on the lighting application. They are optimized for use in single- or dual-display phones, as well as large display PDA phones. Each features three general-purpose input/outputs (GPIOs) to trigger lighting functions such as flash or to control additional device-enable signals. The LP3958 features 70 mA of output current for powering display backlight LEDs and the LP5526 features 150 mA of output current for powering display backlight and flash LEDs. Both devices include an I2C interface.
Typical Application LP3958
Technical Features of National’s LP3958 and LP5526 LMUs
In single and dual displays, the LP3958 LMU drives up to eight white LEDs grouped as four series-connected LEDs per string, with typically one string per display. Display backlight fade in and fade out is controlled via a two-wire, low-voltage, I2C-compatible interface, allowing easy software implementation. The GPIO functions enable the user to control external devices. The serial interface reduces the wire count through the hinge in flip cell phone designs. For keypads, three series-connected LED strings of up to four LEDs each can be independently controlled to enable light segmentation. This is particularly useful in gaming and navigation applications, for example, in which individual buttons can be selected for illumination.
The LP5526 has the same features and packaging as the LP3958 and can drive multi-die serial-flash LEDs in camera Flash (up to 3W of power) and torch applications. Also, in the case of a software problem, the LP5526 features an internal safety timer to protect flash LEDs from aging. With the LP5526, the Flash LED output can also be used to drive single or series-connected RGB LEDs.
Availability, Packaging and Pricing
The LP3958 and LP5526 are available now in 2.5 mm by 2.5 mm, 25-bump micro SMD packages. The LP3958 is priced at $1.60 each and the LP5526 is priced at $2.00 each in 1,000-unit quantities.
