Fairchild Semiconductor’s digitally programmable buck regulator gives system design engineers a highly efficient power management solution for new Dynamic Voltage Scaling (DVS) platforms found in today’s cell phones, portable media players (PMPs) and other portable applications. The FAN5355 device is a high-frequency, ultra-fast transient response, synchronous step-down DC-DC converter optimized for low-power applications using small, low-cost inductors and capacitors. The FAN5355 supports up to 800mA or 1A load current. The device is ideal for mobile phones and similar portable applications powered by a single-cell Lithium-Ion battery. With an output voltage range adjustable via I2C™ interface from 0.75V to 1.975V, the device supports low-voltage DSPs and processors, core power supplies in smart phones, PDAs, and handheld computers.

The FAN5355, an 800mA/1000mA 3MHz Buck converter, has been designed with a proprietary ultra-fast architecture that consumes very low quiescent current and yet delivers ultra-fast transient response. Typical quiescent current in PFM mode is 37µA and even with this meager standby current, the FAN5355 is able to provide best-in-class transient response, making the application more resilient to unexpected fluctuations in load. In addition, this architecture creates lower ripple during PFM mode, reducing system noise and drastically improving light load efficiency to 85 percent even at loads of only 1mA. For more moderate to heavy loads, careful optimization of the power train contributes to a conversion efficiency of more than 90 percent during PWM mode.

During start-up, the IC controls the output slew rate to minimize input current and output overshoot at the end of soft-start. The IC maintains a consistent soft-start ramp, regardless of output load during start-up. During light-load conditions, the regulator includes a PFM mode to enhance light-load efficiency. The regulator transitions smoothly between PWM and PFM modes with no glitches on VOUT. Normal PFM (NPFM) mode offers the lowest quiescent current, at the expense of setpoint accuracy. Enhanced PFM (EPFM) mode features higher accuracy, as well as a 25kHz minimum PFM frequency, designed to prevent the regulator from operating in the audible range. In shutdown, the current consumption is reduced to less than 2µA, using software shutdown (EN = 1 with EN_DCDC = 0), and less than 200nA in hardware shutdown (EN = 0).

The FAN5355 is equipped with an I2C interface allowing the system to dynamically adjust the digital core’s power supply voltage based on the processor workload. Typical cores benefiting from DVS are application processors, graphics processors and DSPs in mobile applications. By tailoring the power supply voltage level to the processing state of the core, energy consumption is reduced leading to longer battery life. In order to maximize the effectiveness of the DVS, the FAN5355’s digitally programmable output voltage has a range of 0.75V to 1.975V and can be adjusted in 12.5mV increments. To accommodate the needs of portable applications, the FAN5355 is available in 3mm x 3mm MLP packaging and 12 bump, 0.5mm pitch WL-CSP packaging. The chip’s advanced protection features include short-circuit protection and current and temperature limits. During a sustained over-current event, the IC shuts down and restarts after a delay to reduce average power dissipation into a fault.

The FAN5355 utilizes lead-free (Pb-free) terminals and has been characterized for moisture sensitivity in accordance with the Pb-free reflow requirements of the joint IPC/JEDEC standard J-STD-020. All of Fairchild’s products are designed to meet the requirements of the European Union’s Directive on the restriction of the use of certain substances (RoHS). The FAN5355 operates at 3MHz (nominal) fixed switching frequency using either its internal oscillator or external SYNC frequency. It is available in 10-lead MLP (3×3mm) and 12-bump CSP packages.

Related products

• Wide input DC/DC converters
• Dual-channel synchronous step-down converter