飞兆FAN5355 3MHz可编电源方案

飞兆(Fairchild)公司的FAN5355是工作在3MHz的1A/0.8A数字可编TinyBuck稳压电源,可提供1A或0.8A的输出电流.在轻负载时,器件工作在节电的PFM模式,并能从固定频率的PWM自动转换成可变频率PFM模式,从而获得最大的效率,在3MHz时的效率为91%. FAN5355集成了I2C兼容的接口,输出电压从0.75V到1.95V,支持低压DSP和处理器,手机,PDA和手提设备中的核电源.本文介绍了FAN5355主要特性,方框图以及典型应用电路图.

FAN5355:1A / 0.8A, 3MHz Digitally Programmable TinyBuckTM Regulator
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(1) 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 operates at 3MHz (nominal) fixed switching frequency using either its internal oscillator or external SYNC frequency.
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 serial interface is compatible with Fast/Standard and High-Speed mode I2C specifications, allowing transfers up to 3.4Mbps. This interface is used for dynamic voltage scaling with 12.5mV voltage steps, for reprogramming the mode of operation (PFM or Forced PWM), or to disable/enable the output voltage.

The chips 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.
During start-up, the IC controls the output slew rate to minimize input current and output overshoot at the end of softstart. The IC maintains a consistent soft-start ramp, regardless
of output load during start-up.

The FAN5355 is available in 10-lead MLP (3x3mm) and 12-bump CSP packages.

FAN5355主要特性:
91% Efficiency at 3MHz
800mA or 1A Output Current(1)
2.7V to 5.5V Input Voltage Range
6 or 7-bit VOUT Programmable from 0.75 to 1.975V
3MHz Fixed-Frequency Operation
Excellent Load and Line Transient Response
Small Size, 1μH Inductor Solution
±2% PWM DC Voltage Accuracy
35ns Minimum On-Time
High-Efficiency, Low-Ripple, Light-Load PFM
Smooth Transition between PWM and PFM
37μA Operating PFM Quiescent Current
Software Selectable 25kHz Minimum PFM Frequency
Prevents Audible Noise in PFM Mode
I2C™-Compatible Interface up to 3.4Mbps
Pin-Selectable or I2C™ Programmable Output Voltage
On-the-Fly External Clock Synchronization
10-lead MLP (3 x 3mm) or 12-bump CSP Packages
FAN5355应用:
SmartReflex-Compliant Power Supply
Split Supply DSPs and μP Solutions OMAP, XSCALE
Cell Phones, Smart Phones, PDAs, Digital Cameras, and Portable Media Players
Micro DC-DC Converter Modules
Handset Graphic Processors (NVIDIA, ATI)



图1. FAN5355方框图



图2.FAN5355典型应用电路