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LM34919B 数据表(PDF) 11 Page - National Semiconductor (TI) |
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LM34919B 数据表(HTML) 11 Page - National Semiconductor (TI) |
11 / 20 page 30102734 FIGURE 1. Start Up Sequence Functional Description The LM34919B Step Down Switching Regulator features all the functions needed to implement a low cost, efficient buck bias power converter capable of supplying at least 0.6A to the load. This high voltage regulator contains an N-Channel buck switch, is easy to implement, and is available in micro SMD package. The regulator’s operation is based on a constant on- time control scheme, where the on-time is determined by V IN. This feature allows the operating frequency to remain relatively constant with load and input voltage variations. The feedback control requires no loop compensation resulting in very fast load transient response. The valley current limit de- tection circuit, internally set at 0.64A, holds the buck switch off until the high current level subsides. This scheme protects against excessively high current if the output is short-circuited when V IN is high. The LM34919B can be applied in numerous applications to efficiently regulate down higher voltages. Additional features include: Thermal shutdown, V CC under-voltage lockout, gate drive under-voltage lockout, and maximum duty cycle limiter. Control Circuit Overview The LM34919B 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 ref- erence (2.5V). If the FB voltage is below the reference the buck switch is turned on for a time period determined by the input voltage and a programming resistor (R ON). Following the on-time the switch remains off until the FB voltage falls below the reference but not less than the minimum off-time. The buck switch then turns on for another on-time period. Typi- cally, during start-up, or when the load current increases suddenly, the off-times are at the minimum. Once regulation is established, the off-times are longer. When in regulation, the LM34919B operates in continuous conduction mode at heavy load currents and discontinuous conduction mode at light load currents. In continuous con- duction mode current always flows through the inductor, nev- er reaching zero during the off-time. In this mode the operating frequency remains relatively constant with load and line variations. The minimum load current for continuous con- 11 www.national.com |
类似零件编号 - LM34919B |
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类似说明 - LM34919B |
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