A4403: Valley Current Mode Control Buck Converter

The A4403 is a buck converter that uses valley current-mode control. This control scheme allows very short switch on-times to be achieved, making it ideal for applications that require high switching frequencies combined with high input voltages and low output voltages.

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

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

When power is initially applied and the device is enabled, a user-configurable soft-start function occurs to minimize 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 provide to ensure correct operation at light loads.

Internal diagnostics provide comprehensive protection against overcurrents, input undervoltages, and overtemperatures.

The device package is a 16-contact, 4 mm × 4 mm, 0.75 mm nominal overall height QFN, with exposed pad for enhanced thermal dissipation. It is lead (Pb) free, with 100% matte tin leadframe plating.