Blinking ICs take a dim view of LEDs

Two new series of I2C general purpose I/O expanders are optimised for controlling LED dimming and blinking in products ranging from mobile phones to servers.

Two new series of I2C general purpose I/O expanders (PCA953x and PCA955x) are optimised for controlling LED dimming and blinking in products ranging from mobile phones to servers in computing, communication and networking applications.

These new 2, 4, 8 and 16bit devices represent an innovation in I2C capabilities, allowing designers an easier way to build systems with more dimming or blinking LEDs than previously possible using just basic general purpose I/Os (GPIO) or microcontrollers (MCUs).

Manufacturers of applications such as cellphones and servers are increasingly requiring multiple blinking LEDs for eye-catching keypad lighting applications, as well as practical purposes such as status indication.

The new PCA953x LED dimmers and PCA955x LED blinkers allow more system flexibility by offloading the LED power consumption and eliminating the programming of the MCU.

"The Philips' PCA955x family is exactly what we've been looking for to control the maintenance and control bus LEDs in our next generation server platform", said Wally Tuten, Senior Engineer, X-series Server Development of IBM.

"With these new parts from Philips, customers and field repair technicians can troubleshoot our systems without having to be in the normal operating mode".

For example in IBM's current product offerings, the memory card can be removed from the system where the DIMM LEDs are obstructed from view from the top of the system.

Using a "super-cap" as a battery to maintain power continuity, the last settings in the PCA955x enable specific control of the individual LEDs' blink rates as well as on/off status, making it much easier to trace and locate specific faults.

This capability allows placement of secondary or tertiary LEDs on the different cards and components to assist in rapid troubleshooting, even after disassembly or with the system AC power off.

"This approach allows for a simpler, but more robust system design and shortens development time, allowing IBM to get its products to market faster and provide better quality debug aids for the customer", according to Tuten.

The new I2C devices have an internal oscillator with four 8bit (256 values) internal registers that are used to set two programmable blink rates.

This removes the need for the MCU to use one of its timers to send repeated commands to "blink" LEDs (repeatedly turning individual LEDs on and off).

It also significantly reduces the I2C bus traffic compared with when a standard GPIO is used to blink or dim the LED, freeing up the I2C bus for additional traffic and control of additional devices.

Once programmed, the internal oscillator allows the I2C bus to be disconnected from the PCA953x or PCA955x with the LED continuing to be dimmed or blink, something not possible with normal GPIOs.

"I2C/SMBus has become the de facto standard serial bus for maintenance, control and configuration in most electronic platforms ranging from computing applications to networking and communications", said Pierre-Yves Lesaicherre, General Manager, Interface Products Business Line, Philips Semiconductors.

"With these new families of PCA955x and PCA953x I2C LED blinkers and dimmers, we are introducing significant innovation in a mature technology, enabling electronics manufacturers to more simply blink and/or dim LEDs in their systems, while freeing up the microcontroller and the I2C bus for more efficient operation of the system".

The PCA953x LED dimmers have a frequency range from 160Hz to once every 1.6s, with a duty cycle range of completely off to 99.4% on allowing both dimming and blinking of LEDs.

The PCA955x LED blinkers have a frequency range from 40Hz to once every 6.4s with a duty cycle range of 0.6% off to completely on, that allows designers to set, for example, a 4s blink rate with the LED on for 1s and then off for 3s.

Output drive strength is 25mA per bit at 5V operation and 100mA for 8bit groups, which is much more than the amount of current typically allowed by a MCU.

The devices operate between 2.3 and 5.5V and up to a 400kHz I2C bus speed.

Any I/O pins not used as outputs can be configured and used as normal general-purpose inputs.

The 8-pin PCA9550 2bit LED blinker, 16-pin PCA9551 8bit LED blinker, 24-pin PCA9552 16bit LED blinker/PCA9532 16bit LED dimmer and 8-pin PCA9553 4bit LED blinker are available now.

The 8-pin PCA9530 2bit LED dimmer, 16-pin PCA9531 8bit LED dimmer and 8-pin PCA9533 4bit LED dimmer are sampling now with releases through the end of the year.

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