In the world of ICs with zillions of transistors, it's refreshing to learn about the introduction of a simple IC. Fairchild Semiconductor now offers designers a 5-pin LED flasher device, the FAN5646, that will operate on its own and flash an LED. Engineers often use a flashing LED to indicate a device remains ready for an operation, has dropped into a low-power "sleep" mode, or to indicate a setting for a piece of equipment. Some MP3 players and Bluetooth earpieces include this type of flashing LED.

Often, designers have used a microcontroller (MCU) output to drive an LED, but that approach keeps the MCU active to some extent because it must update its output pin with a timed flash pattern and use instructions to control the I/O port. So, the overall circuit can use more power than it should. Also, this approach could require an FET to drive the LED and a low-dropout regulator to supply power.

The Fairchild FAN5646 requires only a current-control resistor and a decoupling capacitor. The resistor sets the rise and fall time for the LED's intensity, so the LED can turn on or off in a "soft-flash" pattern, basically a logarithmic ramp for the on and off conditions. (An abrupt bang-on, bang-off pattern can get annoying.)

A control input (CTRL) lets an MCU or other circuit operate the LED in two ways. In Mode 01, logic levels at the CTRL input will turn the LED on or off with the preset rise and fall times. In Mode 00, the CTRL remains at a logic 1 to cause the flasher circuit to continually repeat the pattern of on-off-on... So you still need an MCU output, but the MCU can drop into a deep-sleep mode instead of awakening periodically to check a counter or timer and control an external LED-control circuit.

For the datasheet, visit: www.fairchildsemi.com/ds/FA/FAN5646.pdf.

The August 2009 data sheet for the FAN5646 notes that developers can use a single-wire TinyWire connection to program the LED's two on times and the period between those two times. But it doesn't provide programming details. A footnote on the datasheet explains, "Contact a Fairchild Semiconductor sales representative for additional performance information and specifications."

I called my Fairchild contact and will report back with an update when I learn more about the TinyWire interface and the programming protocol.
--Jon Titus