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UCC28250RGPT Datasheet(PDF) 11 Page - Texas Instruments |
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UCC28250RGPT Datasheet(HTML) 11 Page - Texas Instruments |
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11 / 53 page  0.3V SS EN UVLO CLK UCC28250 www.ti.com SLUSA29C – APRIL 2010 – REVISED JULY 2011 DETAILED PIN DESCRIPTIONS VDD (5/12) The UCC28250 can be powered up by a wide supply range from 4.3 V (UVLO rising typical) to 20 V (absolute maximum), making it suitable for primary-side control or secondary-side control. When the voltage at the VDD pin is lower than 4.1 V (typical), the controller is in stand-by mode and consumes 150 µA (typical) at 3.6 V VDD. In stand-by mode, VREF continues to be regulated to 3.3 V or follows VDD if VDD is lower than 3.3 V. Please refer to the VREF description for more detailed information. A minimum 1- µF bypass capacitor is required from VDD to ground. Keep the bypass capacitor as close to the device as possible. VREF (Reference Generator) (20/7) The VREF pin is regulated at 3.3 V. An external ceramic capacitor must be placed as close as possible to the VREF and GND pins for noise filtering and to provide compensation to the regulator. The capacitance range must be limited between 0.5 µF to 2 µF for stability. This reference is used to power the controller’s internal circuits, and can also be used to bias an opto-coupler transistor, an external house-keeping microcontroller, or other peripheral circuits. This reference can also be used to generate the reference for an external error amplifier. This regulator output is internally current limited to 25 mA (typical). EN (Enable Pin) (18/5) The following conditions must be met before the controller allows start up: 1. VDD voltage is above the rising UVLO threshold 4.3 V (typical); 2. The 3.3-V reference voltage output at the VREF pin is available and above 2.4 V (typical); 3. Junction temperature is below the thermal shutdown threshold 130 °C (minimum); 4. The voltage at OVP is below 0.7 V (typical). If all these conditions are met, the signal driving the EN pin is able to initiate the soft start process. Once the device is enabled, the 27- µA internal charging current at the SS pin is turned on and begins to charge the soft-start capacitor. The EN pin can accept both level-enable and pulse-enable signals. For level-enable, the voltage level on the EN pin needs to be continuously higher than 2.25 V to allow continuous operation. Once the EN pin falls below 2.25 V, the device is disabled (see Figure 3). Figure 3. Level Enable at EN pin Copyright © 2010–2011, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Link(s): UCC28250 |
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