Buck-boost regulator manages power flow in smartphones/portables

September 02, 2016 // By Graham Prophet
FAN49103 is a digitally programmable buck-boost regulator for the power supplies used in smartphones, tablets and other battery-powered mobile devices, offering reduced board space with a small solution size, claimed as 84% smaller than its closest competitor; Fairchild says, “the FAN49103 can also solve the excessive heat and brownout issues that designers of mobile devices strive to overcome.”

Using full-bridge architecture with synchronous rectification, the FAN49103 can output up to 2.5A while regulating the output at 3.4V. It exhibits seamless transition between step-up and step-down modes reducing output disturbances. The output voltage and operation mode of the regulator can be programmed through an I ²C interface.


At moderate and light loads, Pulse Frequency Modulation (PFM) is used to operate the device in power-save mode to maintain high efficiency. In PFM mode, the part still exhibits excellent transient response during load steps. At moderate to heavier loads or forced PWM mode, the regulator switches to PWM fixed-frequency control. While in PWM mode, the regulator operates at a nominal fixed frequency of 1.8 MHz, which allows for reduced external component values.

Features include;


24 µA Typical PFM Quiescent Current

Above 95% Efficiency

Total Layout Area = 11.61 mm ²

Input Voltage Range: 2.5 V to 5.5 V

Maximum Continuous Load Current:

2.5 A at VOUT=3.4 V, VIN=3.6 V

2 A at VOUT=3.4 V, VIN=2.5 V

I²C Compatible Interface

Programmable Output Voltage:

2.8 V to 4.0 V in 25 mV Steps

1.8 MHz Fixed-Frequency Operation in PWM Mode

Automatic / Seamless Step-up and Step-down Mode Transitions

Forced PWM and Automatic PFM/PWM Mode Selection

0.5 µA Typical Shutdown Current


The FAN49103 can reduce thermal issues by providing a system power rail at the lowest possible voltage, reducing or eliminating heatsinks. Fast transient response counters brownouts by enabling larger pulsed loads to be supported, which reduces the effect of battery droop. It supports large loads up to 2.5A DC and can maintain a constant regulated output over the entire battery range so the system will operate normally despite battery sags.


The FAN49103 comes in a 20-bump WLCSP package 1.6 x 2.0mm.


Fairchild; fairchildsemi.com/mobile