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LM34914 Arkusz danych(PDF) 7 Page - Texas Instruments |
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LM34914 Arkusz danych(HTML) 7 Page - Texas Instruments |
7 / 21 page UVLO VIN VCC SW Pin Inductor Current SS Pin t2 VOUT 7.0V 2.5V t1 LM34914 www.ti.com SNVS453A – MAY 2007 – REVISED DECEMBER 2007 Figure 2. Startup Sequence Functional Description The LM34914 Step Down Switching Regulator features all the functions needed to implement a low cost, efficient buck bias power converter capable of supplying at least 1.25A to the load. This high voltage regulator contains an N-Channel buck switch, is easy to implement, and is available in the thermally enhanced 3mm x 3mm LLP-10 package. The regulator’s operation is based on a constant on-time control scheme where the on-time is determined by VIN. This feature results in the operating frequency remaining relatively constant with load and input voltage variations. The feedback control scheme requires no loop compensation resulting in very fast load transient response. The valley current limit scheme protects against excessively high currents if the output is short circuited when VIN is high. To aid in controlling excessive switch current due to a possible saturating inductor the valley current limit threshold changes with input and output voltages, and the on-time is reduced by approximately 50% when current limit is detected.The LM34914 can be applied in numerous applications to efficiently regulate down higher voltages. Additional features include: Thermal shutdown, VCC under-voltage lock- out, gate drive under-voltage lock-out, and maximum duty cycle limit. Control Circuit Overview The LM34914 buck DC-DC regulator employs a control scheme based on a comparator and a one-shot on-timer, with the output voltage feedback (FB) compared to an internal reference (2.5V). If the FB voltage is below the reference the buck switch is switched on for a time period determined by the input voltage and a programming resistor (RON). Following the on-time the switch remains off until the FB voltage falls below the reference, but not less than the minimum off-time forced by the LM34914. The buck switch is then turned on for another on-time period. Copyright © 2007, Texas Instruments Incorporated Submit Documentation Feedback 7 Product Folder Links: LM34914 |
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