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 discontinuous 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 inversely proportional to the output voltage. This action is automatically controlled by an internal feedback loop and reference. The cascaded configuration allows a voltage 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 programmed for other output voltages less than 18V with a few additional components. An isolated version can be achieved with this topology as described further in Unitrode Application Note U-149.

• 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

• Topology
• Flyback
• Duty cycle (Max) (%)
• 55
• Supply voltage (Max) (V)
• 9.3
• UVLO thresholds on/off (V)
• 8.4/6.3
• Features
• Constant on-time, Error Amplifier, Green Mode, Light Load Efficiency, Soft Start
• Operating temperature range (C)
• -40 to 85
• Rating
• Catalog
• Frequency (Max) (kHz)
• 250
• Gate drive (Typ) (A)
• 0.2

UCC2889的完整型号有：UCC2889D、UCC2889DTR，以下是这些产品的关键参数及官网采购报价：

UCC2889D，工作温度：-40 to 85，封装：SOIC (D)-8，包装数量MPQ：75个，MSL 等级/回流焊峰值温度：Level-2-260C-1 YEAR，引脚镀层/焊球材料：NIPDAU，TI官网UCC2889D的批量USD价格：1.064（1000+）

UCC2889DTR，工作温度：-40 to 85，封装：SOIC (D)-8，包装数量MPQ：2500个，MSL 等级/回流焊峰值温度：Level-2-260C-1 YEAR，引脚镀层/焊球材料：NIPDAU，TI官网UCC2889DTR的批量USD价格：.906（1000+）

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