Intersil – Flower Power Reference Design Demonstrates Efficiency of Switching Regulator in Low-Current Applications

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Intersil, a Renesas company, has debuted the ‘Flower Power’ reference design which demonstrates the capabilities of its ISL85005 high-efficiency synchronous buck regulator, as well as other Intersil analog and sensing products. It showcases a diverse portfolio of products for broad market applications. From power management to precision analog and specialty ICs, Intersil can power-up your most challenging designs.

The reference design board is intended to be a fun office adornment. A press of the button on the back powers up the board; the flower will then play one of five classic ‘Summer of Love’ songs and create an eye-catching pattern by driving the color LEDs mounted on the petals of the flower- shaped board.

At the heart of the Flower Power reference design is Intersil’s 5A ISL85005, a switching regulator with an input-voltage range of 4.5V to 18V, this is ideal for use with the board’s two CR2032 batteries, which in series produce a nominal output voltage of 6V.

Technical Overview:
Battery: The board is powered by two CR2032 3V batteries in series. This produces a nominal voltage of 6.0V with 240mA/hrs of life. The output of the battery voltage is fed to the ISL85005 by the means of a power- down control circuit. A fresh set of batteries should be able to power this reference design for >1000 song cycles before they’ll reach a low battery condition.

Power-Down Control Circuit: The board is powered on by pressing the push button on the back of the board. In order to extend the battery lifespan, the board will turn itself off after the song and LED pattern has completed (approximately 30 seconds). This is accomplished by utilizing a couple of bi-polar transistors and a signal from the microcontroller. When power is applied, the microcontroller signal goes high. After completing the song pattern, the microcontroller drives the pin low and the circuit disconnects the battery from the ISL85005.

DC/DC: The ISL85005 is used to produce 3.3V to power the rest of the board. The design follows the reference design from the evaluation board/ datasheet. While the ISL85005 is capable of delivering 5A, this design actually draws less than 50mA on the 3.3V rail. An Abracon 3.3μH power inductor was used in conjunction with the ISL85005.

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Low Battery Detect: The low battery detect circuit uses the ISL21080 voltage reference and ISL28915 comparator. The battery voltage is divided down and compared to the 2.048V output of the ISL21080. If the battery voltage drops below 4.72V, the output of the comparator goes HIGH and the microcontroller commands all 5 LEDs to flash red. Since the batteries will last for over 1000 song cycles, demonstration of this low power circuit is best done by removing the batteries and powering the board with a programmable power supply set below 4.72V.

Ambient Light Sensor: The flower board is populated with the ISL29102 light-to-voltage sensor. This does not operate as a normal sensor but does generate random numbers in the microcontroller. At power up, the micro reads the output of the ambient light sensor and then feeds that value as the seed for a random number generator. This enables the board to play a random song rather than repeat a pattern of songs.

LEDs: The LEDs used on this board are tri-color LEDs. Each LED package actually contains a red, green and blue LED. A different value of pull-up resistor was chosen for each color in order to create an equal light intensity out of each color. The microcontroller has control over each color and can therefore produce any color of the rainbow by changing the duty cycle of each RGB control line. For the reference design, there are 4 different LED patterns that can be used. At power up both the song and the LED pattern are chosen at random. The LEDs change color/intensity on each beat of the song.

FEATURES
• ISL29102 low power ambient light-to-voltage, non-linear converter
• ISL21080 300nA nano power voltage reference
• ISL28915 nano power push/pull output comparator
• Abracon ASPI-0630LR power inductor, offering low DC resistance and high saturation current
• Murata PKLCS1212E4001-R1 surface-mount piezoelectric sounder

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