Intersil is ready for the cold with a full lineup of power and analog components specified to operate down to -40 degrees C. Just in time for the holidays, you can get a Limited Edition 2016 Snowflake Ornament reference design to celebrate. This ornament is up for the challenge of hanging on a tree from Fargo, ND to Helsinki, Finland.
The ornament has a series of LEDs that fade on and off in an eye-pleasing pattern and plays the familiar song “Let it Snow, Let it Snow, Let it Snow†via a small buzzer when the button on the back of the board is pressed. The brightness of the LEDs adjusts to the ambient light in the room in order to keep the brightness appropriate to the surroundings.
Additionally, there is a low-battery detect feature as well as a 4-hour time-out alert to remind the user to turn off the ornament and avoid depleting the batteries. The ornament is powered by two AAA batteries and is light-weight enough to prominently hang on a tree via a hole at the top of the ornament with the included ribbon.
Featured devices include: The ISL91127IR buck boost converter used to maintain constant voltage output with changing battery input. The ISL91127IR is one of Intersil’s latest buck-boost converters and features operation from 1.8V to 5.5V, typical quiescent current of 30μA, up to 96% efficiency and is packaged in a small but easy-to-use 4x4mm QFN. These features are a perfect fit for the design. If Lithium AAA batteries are installed, the initial voltage will be as high as 3.4V and, in this case, the ISL91127IR will function in buck mode, will switch to buck-boost mode and then eventually into pure boost mode as the batteries deplete. The ornament will continue to function until the batteries are fully depleted and drop down to 1.8V output.
Although the ornament functions normally all the way down to 1.8V, the user is alerted at 2V that the batteries will soon need to be changed. In order to detect this low battery condition, two Intersil devices are used. The ISL60002-20 voltage reference provides a very stable 2.048V reference to the negative terminal of the ISL28915 voltage comparator.
When the battery voltage drops below 2.048V, the output of the comparator is driven high and the microcontroller is alerted of a low battery condition. In low-battery mode the LEDs strobe to form a large “X†and indicate that the batteries need to be replaced. The ISL28915 comparator has a 1.8V to 5.5V supply range, a 6 lead SOT-23 package and has an active current of 600nA. The ISL60002-20 voltage reference features an operating voltage of 2.7V to 5.5V, 3 lead SOT-23 and active current of 350nA typical.
In order to adjust the brightness of the LEDs for the operating environment, an ambient light sensor (ALS) is employed. The ISL29102 is a great choice because it has a spectral response very close to the human eye requires no external components and has very low operating current of 650nA to 10μA depending on the ambient light in the room. The ISL29102 also operates on 1.8- 3.3V voltage rails and comes in a 2x2.1mm 6 lead ODFN package. The output of the ISL29102 is fed to the microcontroller’s A/D converter and the LED light intensity is adjusted by changing the maximum duty cycle of each LED string.
The ambient light sensor is powered by a 3.0V rail rather than the 3.3V rail of the rest of the board. While the ISL29102 can be powered by the 3.3V rail as well, the 3.0V rail produced by the ISL80505 low drop-out regulator provides a low noise supply to the sensor. The intent is primarily to serve as a reminder that Intersil has low linear regulators that are excellent candidates anywhere a low noise voltage source is required. In this case, the ISL80505 is a 500mA regulator with a drop-out as low as 45mV, has excellent accuracy and PSRR, and is packaged in an 8 lead DFN.
Finally, the ornament includes an ATMEGA328P-AU microprocessor from Atmel to play the music and control the blinking pattern of the LEDs.
