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LTM8063 数据表(PDF) 15 Page - Linear Technology |
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LTM8063 数据表(HTML) 15 Page - Linear Technology |
15 / 24 page LTM8063 15 8063fa For more information www.linear.com/LTM8063 APPLICATIONS INFORMATION The internal current limit is designed to prevent damage to the LTM8063 in the case of overload or short-circuit. The internal temperature of the LTM8063 depends upon operating conditions such as the ambient temperature, the power delivered, and the heat sinking capability of the system. For example, if the LTM8063 is configured to regulate at 1.2V, it may continuously deliver 2.5A from 12VIN if the ambient temperature is controlled to less than 55°C. This is higher than the 2A continuous rating. Please see the “Derating, VOUT = 1.2V” curve in the Typical Per- formance Characteristics section. Similarly, if the output voltage is 15V and the ambient temperature is 100°C, the LTM8063 will deliver less than 100mA from 36VIN, which is less than the 2A continuous rating. Load Sharing The LTM8063 is not designed to load share. Burst Mode Operation To enhance efficiency at light loads, the LTM8063 auto- matically switches to Burst Mode operation which keeps the output capacitor charged to the proper voltage while minimizing the input quiescent current. During Burst Mode operation, the LTM8063 delivers single cycle bursts ofcurrenttotheoutputcapacitorfollowedbysleepperiods where most of the internal circuitry is powered off and energy is delivered to the load by the output capacitor. During the sleep time, VIN quiescent current is greatly reduced, so, as the load current decreases towards a no load condition, the percentage of time that the LTM8063 operates in sleep mode increases and the average input current is greatly reduced, resulting in higher light load efficiency. Burst Mode operation is enabled by tying SYNC to GND. Minimum Input Voltage The LTM8063 is a step-down converter, so a minimum amount of headroom is required to keep the output in regulation. Keep the input above 3.2V to ensure proper operation. Voltage transients or ripple valleys that cause the input to fall below 3.2V may turn off the LTM8063. Output Voltage Tracking and Soft-Start The LTM8063 allows the user to adjust its output voltage ramp rate by means of the TR/SS pin. An internal 2μA pulls up the TR/SS pin to about 2.4V. Putting an external capaci- tor on TR/SS enables soft starting the output to reduce current surges on the input supply. During the soft-start ramp the output voltage will proportionally track the TR/ SS pin voltage. For output tracking applications, TR/SS can be externally driven by another voltage source. From 0V to 0.77V, the TR/SS voltage will override the internal 0.77V reference input to the error amplifier, thus regulat- ing the FB pin voltage to that of the TR/SS pin. When TR/ SS is above 0.77V, tracking is disabled and the feedback voltage will regulate to the internal reference voltage. The TR/SS pin may be left floating if the function is not needed. An active pull-down circuit is connected to the TR/SS pin which will discharge the external soft-start capacitor in the case of fault conditions and restart the ramp when the faults are cleared. Fault conditions that clear the soft-start capacitor are the RUN pin transitioning low, VIN voltage falling too low, or thermal shutdown. Pre-Biased Output As discussed in the Output Voltage Tracking and Soft- Start section, the LTM8063 regulates the output to the FB voltage determined by the TR/SS pin whenever TR/ SS is less than 0.77V. If the LTM8063 output is higher than the target output voltage, the LTM8063 will attempt to regulate the output to the target voltage by returning a small amount of energy back to the input supply. If there is nothing loading the input supply, its voltage may rise. Take care that it does not rise so high that the input voltage exceeds the absolute maximum rating of the LTM8063. Frequency Foldback The LTM8063 is equipped with frequency foldback which actstoreducethethermalandenergystressontheinternal power elements during a short circuit or output overload condition. If the LTM8063 detects that the output has fallenoutofregulation,theswitchingfrequencyisreduced as a function of how far the output is below the target voltage. This in turn limits the amount of energy that can |
类似零件编号 - LTM8063 |
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类似说明 - LTM8063 |
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