The UCC28230, UCC28231 PWM bus controllers are optimized for use in high efficiency, high power density, unregulated intermediate bus converters. Topologies include push-pull, half-bridge and full-bridge. External drivers, such asthe UCC27200 120-V high-side/low-side drivers, can be used with this controller.

Low cost, small size and highly efficient solutions are provided by innovations such as:

• Start-up frequency control circuit allowing small output inductor andthe ability to start with large intermediate bus capacitor.
• Load depended off-time control set by user.

Additional 1-D control outputs can be used for primary winding clamping in self-driven output synchronous rectifier applications or as drive signals for the control-driven synchronous rectifier.

Cycle-by-cycle current limit prevents overstresses of converter. If the over current condition causes less than 80% duty cycle at the output, then after a programmed time the controller proceeds into periodical shutdown and restart hiccup mode.

The UCC28230 provides 5 V, and the UCC28231 provides 3.3-V precision reference voltages with 1.5% overall accuracy and 10-mA output current. This reference voltage can be used to supply housekeeping circuit and/or microcontroller. The precision reference voltage can also be used for accurate setting of system parameters.

Other features include under-voltage lockout, thermal shut down, programmable soft start, over-current hiccup mode and short circuit protection with internal restart by default that can be set into latch-off mode by an external resistor.