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LTM8003 Arkusz danych(PDF) 16 Page - Linear Technology |
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LTM8003 Arkusz danych(HTML) 16 Page - Linear Technology |
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16 / 30 page  LTM8003 16 8003fc For more information www.linear.com/LTM8003 OPERATION The LTM8003 is a stand-alone non-isolated step-down switching DC/DC power supply that can deliver up to 6A. The continuous current is determined by the internal operating temperature. It provides a precisely regulated output voltage programmable via one external resistor from 0.97V to 18V. The input voltage range is 3.4V to 40V. Given that the LTM8003 is a step-down converter, make sure that the input voltage is high enough to support the desired output voltage and load current. Simplified Block Diagrams are given on the previous page. The LTM8003 contains a current mode controller, power switching elements, power inductor and a modest amount of input and output capacitance. The LTM8003 is a fixed frequency PWM regulator. The switching frequency is set by simply connecting the appropriate resistor value from the RT pin to GND. An internal regulator provides power to the control cir- cuitry. This bias regulator normally draws power from the VIN pin, but if the BIAS pin is connected to an external voltage higher than 3.2V, bias power is drawn from the external source (typically the regulated output voltage). This improves efficiency. The RUN pin is used to place the LTM8003 in shutdown, disconnecting the output and reducing the input current to a few µA. Toenhanceefficiency,theLTM8003automaticallyswitches to Burst Mode operation in light or no load situations. Between bursts, all circuitry associated with controlling the output switch is shut down reducing the input supply current to just a few µA. TheoscillatorreducestheLTM8003’soperatingfrequency when the voltage at the FB pin is low. This frequency fold- back helps to control the output current during start-up and overload. The TR/SS node acts as an auxiliary input to the error amplifier. The voltage at FB servos to the TR/SS voltage until TR/SS goes above about 0.97V. Soft-start is imple- mented by generating a voltage ramp at the TR/SS pin using an external capacitor which is charged by an internal constant current. Alternatively, driving the TR/SS pin with a signal source or resistive network provides a tracking function. Do not drive the TR/SS pin with a low impedance voltage source. See the Applications Information section for more details. The LTM8003 contains a power good comparator which trips when the FB pin is at about 90% to 110% of its regulated value. The PG output is an open-drain transistor that is off when the output is in regulation, allowing an external resistor to pull the PG pin high. The PG signal is valid when VIN is above 3.4V. If VIN is above 3.4V and RUN is low, PG will drive low. The LTM8003 is equipped with a thermal shutdown that inhibits power switching at high junction temperatures. The activation threshold of this function is above the maxi- mum temperature rating to avoid interfering with normal operation, so prolonged or repetitive operation under a condition in which the thermal shutdown activates may damage or impair the reliability of the device. |
Podobny numer części - LTM8003 |
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Podobny opis - LTM8003 |
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