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UCC2889DTR Datasheet(PDF) 1 Page - Texas Instruments |
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UCC2889DTR Datasheet(HTML) 1 Page - Texas Instruments |
1 / 14 page Off-line Power Supply Controller • Transformerless Off-line Applications • Ideal Primary-side Bias Supply • Efficient BiCMOS Design • Wide Input Range • Fixed or Adjustable Low Voltage Output • Uses Low Cost SMD Inductors • Short Circuit Protected • Optional Isolation Capability The UCC1889 controller is optimized for use as an off-line, low power, low voltage, regulated bias supply. The unique circuit topology utilized in this device can be visualized as two cascaded flyback converters, each operating in the discontinu- ous mode, and both driven from a single external power switch. The significant benefit of this approach is the ability to achieve voltage conversion ratios of 400V to 12V with no transformer and low internal losses. The control algorithm utilized by the UCC1889 is to force the switch on time to be inversely proportional to the input line voltage while the switch off time is made in- versely proportional to the output voltage. This action is automatically controlled by an internal feedback loop and reference. The cascaded configuration allows a volt- age conversion from 400V to 12V to be achieved with a switch duty cycle greater than 10%. This topology also offers inherent short circuit protection since as the output voltage falls to zero, the switch off time approaches infinity. The output voltage can be easily set to 12V or 18V. Moreover, it can be pro- grammed for other output voltages less than 18V with a few additional compo- nents. An isolated version can be achieved with this topology as described further in Unitrode Application Note U-149. UCC1889 UCC2889 UCC3889 SLUS158A - FEBRUARY 1995 - REVISED FEBRUARY 2003 FEATURES DESCRIPTION OPERATION With reference to the application diagram below, when input voltage is first applied, the RON current into TON is directed to VCC where it charges the external capacitor, C3, connected to VCC. As voltage builds on VCC, an internal undervoltage lockout holds the circuit off and the output at DRIVE low until VCC reaches 8.4V. At this time, DRIVE goes high turning on the power switch, Q1, and redirecting the current into TON to the timing capacitor, CT. CT charges to a fixed threshold with a current ICHG=0.8 • (VIN - 4.5V)/RON. Since DRIVE will only be high for as long as CT charges, the power switch on time will be inversely proportional to line voltage. This provides a constant line voltage-switch on time product. Note: This device incorporates patented technology used under license from Lambda Electronics, Inc. TYPICAL APPLICATION UDG-93060-1 |
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