Operation Down to an Input

Voltage of 1.8 V

High Efficiency Boost, SEPIC or

Flyback (Buck-Boost) Topologies

Drives External FETs for

High-Current Applications

Up to 2-MHz Oscillator

Synchronizable Fixed Frequency

Operation

High-Efficiency Low-Power Mode

High-Efficiency at Very Low-Power

with Programmable Variable

Frequency Mode

Pulse-by-Pulse Current Limit

5-μA Supply Current in Shutdown

150-μA Supply Current in Sleep

Mode

Selectable NMOS or PMOS

Rectification

Built-In Power-On Reset

(UCC39422 Only)

Built-In Low-Voltage Detect

(UCC39422 Only)

simplified schematic block diagram and

application circuit

description

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.