Extremely low ripple step-down controllers

Edited by the Electronicstalk editorial team Dec 13, 2006

Versatile, dependable and cost-effective power supplies with output currents of up to 3A can be implemented easily and conveniently using the new XC9220/XC9221 range of step-down DC/DC controller ICs

Versatile, dependable and cost-effective power supplies with output currents of up to 3A can be implemented easily and conveniently using the new XC9220/XC9221 range of step-down DC/DC controller ICs from Torex.

Depending on the model, XC9220 and XC9221 controllers have an internal switching frequency of 300kHz, 500kHz or 1MHz.

These high switching frequencies allow the use of small external components.

In addition, the new controllers are suitable for use with ceramic capacitors which not only provide further space savings but also mean that, because of the inherently low ESR of ceramic components, very low levels of ripple are achieved.

Suitable for operation from DC inputs in the range 2.8V to 16.0V, XC9220 and XC9221 controllers use a 0.9V reference voltage which means that, with external resistors, the output voltage of the supply can be set easily and accurately over a wide range.

These characteristics make the devices an ideal choice in a broad spectrum of applications, including set-top boxes, digital televisions, DVD recorders and notebook computers.

XC9220 devices use PWM control which ensures high efficiency at moderate to high loads, while XC9221 devices switch automatically from PWM to PFM control when lightly loaded ensuring that high efficiency is maintained under all conditions, even in applications involving loads which vary widely.

All devices in the range incorporate short-circuit protection, and all provide a soft-start function.

In many versions the start-up time can be set by the user.

An under-voltage lock out (UVLO) feature is also incorporated which shuts down the supply if the input voltage falls below 2.3V, thereby preventing anomalous operation and ensuring a normal soft start after power dips.

The new controllers are available in SOT-25 and USP-6C packages and require the addition of only a transistor, a coil, a diode and two capacitors to produce a compact high-performance power supply.