The buck converter’s operating frequency is set using a timing resistor and can also be synchronised with an external system clock applied to the same resistor input pin. A wide supply voltage range, 2.95V to 5.5V, makes the AP3440 suited for both 3.3V and 5V bus systems.
Packaged in the thermally enhanced V-QFN3030-16 package and integrating a pair of very low on-resistance N-channel power MOSFETs, the converter is capable of driving a 4A load at an efficiency level as high as 94%. The AP3440 ensures line and load regulation, with its current mode control providing fast transient response and cycle-by-cycle current limit.
The buck converter’s built-in protection features include over-current and over-voltage protection, thermal shutdown, and a programmable under-voltage lockout (UVLO) function. The UVLO level is internally set at 2.6V, but can be increased by programming the threshold using a resistor divider network on the enable pin.
To help minimise inrush currents and to support power-up sequencing, the AP3440 also integrates a soft-start function, programmed via an external capacitor. The inclusion of an open-drain ‘Power Good’ output signals that the device output is within 93% and 107% of its nominal voltage and helps to further reduce circuit footprint.
The AP3440 costs $0.25 (10,000).