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issue: March 2008 APPLIANCE Magazine

Electronics Report
Driving Power Savings

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A new LED driver provides product designers with a low-power, compact solution for blinking LED applications.

The FAN5645 from Fairchild Semiconductor (Portland, ME, U.S.) is a single-wire programmable LED driver designed for blinking LED indicators that require high performance and flexibility in a small footprint. The device records a blinking pattern and plays it indefinitely, eliminating the need for continual system processor control. According to Maurizio Tarsia, senior director at Fair-child, this results in significant energy savings. The driver is said to consume just 33 μA, which the company says is much less than a system processor’s consumption in the mA range.

“The FAN5645 is innovative in that it offers a novel way to save power consumption in common battery-powered applications such as electric toothbrushes, smart phones, cell phones, medical devices, and toys,” Tarsia says. “And since battery-powered applications have increasing power-hungry functionalities on them, the minimal power consumption and cutting-edge technique to save power make this an innovative product.”

Tarsia says a serial interface enables the low power consumption. In addition, the autonomous operation of the LED driver eliminates the need for an interrupt-driven processor to control the sequencing of the LED, freeing up processor bandwidth. The driver is also flexible in that it can be configured in different modes through the control pin: Blinking patterns can run once or continuously, or they can follow the state of the control pin.

Squeezing all of these features into an MLP 3.0 × 3.0-mm package was not an easy task, Tarsia notes. “To overcome this challenge, the design focused on achieving the lowest dropout voltage per unit area possible while still keeping static current to a minimum,” he explains.

With such a compact form factor, the driver is ideal for space-constrained applications. Tarsia offers an example: “Typically in an electric toothbrush, the main processor of a battery-operated system executes a small program that controls the on-off state of the LED,” he explains. “The system processor could be as simple as an 8-bit microcontroller, as in cordless tools and cordless appliances, or a complex baseband chip, as in Bluetooth headsets and cell phones.”

The problem, Tarsia says, is that designers have to keep the processor running to blink an LED, and, in turn, it consumes unwanted power, like when the system is in standby mode. “During normal operation of the system, the FAN5645 records a blinking pattern sent by the main system processor through a serial interface (one control pin),” Tarsia says. “When the system moves in standby mode, the system can be powered down to save power, and the driver blinks the LED autonomously. This consumes much less current than an active system processor, resulting in longer battery life of the battery-powered system.”

The new LED driver utilizes lead-free (Pb-free) terminals and has been characterized for moisture sensitivity in accordance with the Pb-free reflow requirements of the joint IPC/JEDEC standard J-STD-020. It is also designed to meet the requirements of the European Union’s RoHS Directive.

Suppliers mentioned in this article:
Fairchild Semiconductor

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