lowpowerZONE Products for the week of September 17, 2007

Intersil Corporation Says…

ISL8009: World's Most Power-Efficient Integrated FET Buck Regulator Extends Battery Life and Saves Space

Intersil Corporation, a world leader in the design and manufacture of high-performance analog semiconductors, announced the ISL8009, a high-efficiency, 1.5A synchronous buck integrated FET regulator ideal for point-of-load regulation for datacom/telecom, battery powered systems, medical instrumentation and several industrial applications.

The ISL8009 is designed to utilize a special multi-operation capability, allowing selection between forced PWM mode and automatic PWM/PFM mode. This ability to switch between modes enables the regulator to maintain up to 95% efficiency in both full load and light load conditions. Additionally, when the device is in PFM mode, the quiescent current drops to 17µA and makes the ISL8009 ideal for battery powered applications.

The ISL8009 includes features like high 1.6 MHz switching frequency, allowing the use of smaller external components. The device also has internal current mode compensation to eliminate the need for external components while contributing to fast transient response in over current conditions.

EN-Genius Says…

This is the first >1 A synchronous buck regulator I believe I have seen in DFN-8, although Linear offers a 3 A regulator in DFN-10 (LTC3586); most, however, are in 16 pin packages. There have also been many examples of PWM/PFM switchover for high/low loads but this seems to be an extraordinarily good design implementation.

With a 5 V input (maximum is 5.5 V) in PWM mode the ISL8009 is showing about 96% efficiency for a load of 0.25 A and a 3.3 V output, an efficiency that falls to about 92% at full load. With 1.2 V output the corresponding numbers are 88% and 80%.

In PFM mode, again with a 5 V input, the part exhibits an efficiency of up to about 95% with 3.3 V output with with loads from 50 mA to 750 mA, peaking at about 350 mA. with a 1.2 V output the corresponding numbers are about 88%. Remarkable numbers.

The output voltage is set by the normal resistive potential divider from the output rail connected to a feedback pin. The internal reference, and the lowest voltage that can be set, is 0.8 V. The minimum operating voltage is 2.7 V. The switch inductor required is in a range of about 1.0 µH to 4.7 µH, increasing with higher output voltage, all easily realized. A 10 µF output capacitor is suggested which can be X5R or X7R ceramic, and a "starting point" of the same type and size of capacitor is suggested for the input. Current sensing is achieved with the resistance of the internal p-channel MOSFET and an internal current sense amplifier.

Power-on reset is included and there is an enable pin, which can allow for sequencing. The output voltage accuracy (always dependng on the potential divider resistor tolerance) is within 3% while the line regulation is typical at 0.2%/V. The typical Rds(on) values for the p-channel MOSFET and n-channel MOSFET are 0.12 Ω and 0.11 Ω, at 5 V input, respectively.

A very nice implementation of a mid-current synchronous buck regulator with fixed operating frequency and low load efficiency switching. The ISL8009 will do exceptionally well in portable instruments and point-of-load modules.

The ISL8009 is in production in DFN-8 and is priced at $1.52 in 1000-piece lots.

Data Sheet