FEATURES

? User Programmable Soft Start With

Active Low Shutdown

? User Programmable Maximum Duty

Cycle

? Accessible 5V Reference

? Undervoltage Lockout

? Operation to 1MHz

? 0.4A Source/0.8A Sink FET Driver

? Low 100μA Startup Current

DESCRIPTION

The UCC3809 family of BCDMOS economy low power integrated circuits

contains all the control and drive circuitry required for off-line and isolated

DC-to-DC fixed frequency current mode switching power supplies with

minimal external parts count. Internally implemented circuits include

undervoltage lockout featuring startup current less than 100μA, a user accessible

voltage reference, logic to ensure latched operation, a PWM comparator,

and a totem pole output stage to sink or source peak current. The

output stage, suitable for driving N-Channel MOSFETs, is low in the off

state.

Oscillator frequency and maximum duty cycle are programmed with two

resistors and a capacitor. The UCC3809 family also features full cycle soft

start.

The family has UVLO thresholds and hysteresis levels for off-line and

DC-to-DC systems as shown in the table to the left.

The UCC3809 and the UCC2809 are offered in the 8 pin SOIC (D), PDIP

(N), TSSOP (PW), and MSOP (P) packages. The small TSSOP and

MSOP packages make the device ideal for applications where board

space and height are at a premium.