UCC39421

The UCC39421 family of synchronous PWM controllers is optimized to operate from dual alkaline/NiCd cells or a single Lithium-Ion (Li-Ion) cell, and convert to adjustable output voltages from 2.5 V to 8 V. For applications where the input voltage does not exceed the output, a standard boost configuration is used.

For other applications where the input voltage can swing above and below the output, a 1:1 coupled inductor (Flyback or SEPIC) is used in place of the single inductor. Fixed frequency operation can be programmed, or synchronized to an external clock source. In applications where (at light loads) variable frequency mode is acceptable, the IC can be programmed to automatically enter PFM (pulse frequency modulation) mode for an additional efficiency benefit.

Synchronous rectification provides excellent efficiency at high power levels, where N- or P- type MOSFETs can be used. At lower power levels (between 10% and 20% of full load) where fixed frequency operation is required, low power mode is entered. This mode optimizes efficiency by cutting back on the gate drive of the charging FET. At very low power levels, the IC enters a variable frequency mode (PFM). PFM can be disabled by the user.

Other features include pulse-by-pulse current limiting, and a low 5-µA quiescent current during shutdown. The UCC39422 incorporates programmable power-on reset circuitry and an uncommitted comparator for low voltage detection. The available packages are 20-pin TSSOP or 20-pin N for the UCC39422, and 16-pin TSSOP or 16-pin N for the UCC39421.