The UCC3809 family of BCDMOS economy low power integrated circuitscontains all the control and drive circuitry required for off-line and isolatedDC-to-DC fixed frequency current mode switching power supplies withminimal external parts count. Internally implemented circuits includeundervoltage lockout featuring startup current less than 100µA, a user accessiblevoltage reference, logic to ensure latched operation, a PWM comparator,and a totem pole output stage to sink or source peak current. Theoutput stage, suitable for driving N-Channel MOSFETs, is low in the offstate.
Oscillator frequency and maximum duty cycle are programmed with tworesistors and a capacitor. The UCC3809 family also features full cycle softstart.
The family has UVLO thresholds and hysteresis levels for off-line andDC-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 andMSOP packages make the device ideal for applications where boardspace and height are at a premium.
User Programmable Soft Start With Active Low Shutdown