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Buck converter uses valley current-mode control

Posted: 15 Jan 2009     Print Version  Bookmark and Share

Keywords:current-mode  buck converter  low switch  switching frequency 


Allegro MicroSystems, Inc. has expanded its family of general-purpose buck regulators with the introduction of a new 3 A buck converter. This new device uses valley current-mode control. This control scheme allows very low switch on times to be achieved, making it ideal for applications that require high switching frequencies combined with high input voltages (9 V—46 V) and low output voltages (0.8 V—15 V). Allegro's A4403 buck converter is a flexible and cost-effective solution for office automation, industrial and consumer applications.

System cost is reduced through high switching frequencies of up to 2 MHz, allowing smaller and lower value inductors and capacitors. In addition, minimal external components are required through high levels of integration. Optimal drive circuits are utilised to minimise switching losses.

The switching frequency is maintained constant, as the input voltage modulates the on-time. This feed-forward control ensures excellent line correction. An external resistor pulled up to the input supply programs the on-time.

When power is initially applied and the device is enabled, a user-configurable soft-start function occurs to minimise inrush current and to prevent output overshoot. Internal housekeeping and bootstrap supplies are provided which only require the addition of one small ceramic capacitor. A top-off charge pump is also provided to ensure correct operation at light loads. Internal diagnostics provide comprehensive protection against over-currents, input under-voltages, and over-temperature conditions.

Allegro's A4403 is supplied in a 16-contact, 4 mm × 4 mm, 0.75 mm QFN (suffix EU), with exposed pad for enhanced thermal dissipation. It is lead (Pb) free, with 100% matte tin leadframe plating. The A4403 is priced at Rs.38.03 ($0.76) in quantities of 1,000.

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