Power Electronics
Miniature Buck Simplifies IBA and Portable-Power Design

Miniature Buck Simplifies IBA and Portable-Power Design

According to Harvest Wang, Product Line Director of Analog, Mid Power Group, Fairchild Semiconductor’s FAN2106, the first member of the TinyBuck family, is the industry’s smallest synchronous buck regulator. Due to its wide input-voltage range and reduced requirement for external components, the highly integrated module has the potential to simplify intermediate-bus-architecture (IBA) systems. High efficiency and small size also make the device well suited for portable applications. An application circuit is shown in the Figure.

The 3-V to 24-V input, 6-A module can generate output voltages from 0.8 V to 90% of VIN, well suited for IBA applications. Using the module, the total pc-board footprint for a voltage regulator in an IBA system can be less than 2.5 cm2, according to Wang. Board-area savings of up to 50% over discrete solutions are possible.

The module can operate with up to 95% efficiency, and this also enables high overall system efficiencies. For example, 5-V stepdown conversion from a high-voltage system bus (a typical requirement in IBA) can be accomplished with greater than 85% efficiency using the device, according to Wang.

High efficiency and small size also benefit portable power design. Specifically, a light-load power-saving mode compliments the high operating efficiency to extend battery life. Furthermore, the reduced heatsink requirements for the module, in addition to its small size, enable smaller form factors in portable applications.

For loads between 1 A and 6 A, the operating efficiency of the FAN2106 generally ranges between 85% and 95%, and lower switching frequencies tend to increase the operating efficiency of the device. In certain cases (for example, when the input voltage is 8 V, the output voltage is set to 3.3 V, and the switching frequency is 300 kHz) efficiency can rise slightly above 95%. The maximum supported switching frequency is 600 kHz.

The module is packaged in a low-profile MLP-25 package of 5 mm x 6 mm, and integrates a boot diode, a PWM controller, two single-channel MOSFET drivers, and the high-side and low-side power MOSFETs. The MOSFETs were fabricated with Fairchild’s BiCMOS power process, with RDS(ON) being 30 mΩ for the high-side device, and 14 mΩ for the low-side device. The controller includes an internal 800-mV voltage reference with 1% accuracy up to 85°C.

The power inductor, boot capacitor and decoupling capacitors are the only power components external to the device. Other external components are used for control signals, analog signals or device programming. For example, the switching frequency is programmed from a single pin using an external resistor tied to ground. Another pin controls the current-limit trip threshold by the same method.

Available now, the 1000-piece price for the FAN2106 is $3.78. Additions to the TinyBuck family supporting currents above 6 A are planned.

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