DC/DC converters for use with ceramic capacitors

The small on-resistance of these power transistors permits them to obtain high efficiencies for output currents up to 2A.

The XC9242/43 operates with input voltages VIN ranging between 2.7 and 6V, and its output voltage can be set between 0.9V and VIN by using two external resistors.

ICs that use PWM/PFM control (such as the XC9243) can maintain a very low output voltage ripple under all loads conditions, while exhibiting other typical advantages of PWM/PFM control such as a high efficiency over a range of load conditions.

The XC9242/43 series is available with two different switching frequencies, 1.2MHz for applications where a higher efficiency is critical and 2.4MHz where space is at a premium and when high-speed line and load transient responses are required.

The XC9242/43 series will be forced to stop operating by various protection circuits, such as a thermal shutdown circuit when the chip's temperature reaches 150C and a UVLO (Under Voltage Lock Out) circuit when the input voltage decreases below 2.5V.

Both of the above functions are implemented using hysteresis and will allow the XC9242/43 to resume normal operation when the chip's temperature drops below 130C and when the input voltage increases to 2.68V respectively.

In addition to these protections, the XC9242/43 comprises a current limiter that stops the IC when the output current is too high and permits the IC to automatically resume normal operation (following a soft-start procedure) as soon as the over-current condition disappears.

Other features of the XC9242/43 series include a chip-enable pin to turn the IC on and off, a CL discharge function to quickly discharge the output capacitor when the IC is turned off and the high-speed soft-start circuit.

Because of the very low on-resistance of its two built-in power transistors, the XC9242/43 chip dissipates less power and can thus be integrated in a 2.9 x 2.6mm USP-10B package.