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LTM8056 Scheda tecnica(PDF) 10 Page - Linear Technology |
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LTM8056 Scheda tecnica(HTML) 10 Page - Linear Technology |
10 / 28 page LTM8056 10 8056fa For more information www.linear.com/LTM8056 OPERATION The LTM8056 is a standalone nonisolated buck-boost switching DC/DC power supply. The buck-boost topol- ogy allows the LTM8056 to regulate its output voltage for input voltages both above and below the magnitude of the output, and the maximum output current depends upon the input voltage. Higher input voltages yield higher maximum output current. This converter provides a precisely regulated output volt- age programmable via an external resistor divider from 1.2V to 48V. The input voltage range is 5V to 58V, but the LTM8056 may be operated at lower input voltages if SVIN is powered by a voltage source above 5V. A simplified block diagram is given on the previous page. The LTM8056 contains a current mode controller, power switching elements, power inductor and a modest amount of input and output capacitance. The LTM8056 is a fixed frequency PWM regulator. The switching frequency is set by connecting the appropriate resistor value from the RT pin to GND. TheoutputvoltageoftheLTM8056issetbyconnectingthe FB pin to a resistor divider between the output and GND. In addition to regulating its output voltage, the LTM8056 is equipped with averagecurrent control loops for both the input and output. Add a current sense resistor between IIN and VIN to limit the input current below some maximum value. The IINMON pin reflects the current flowing though the sense resistor between IIN and VIN. A current sense resistor between VOUT and IOUT allows the LTM8056 to accurately regulate its output current to a maximum value set by the value of the sense resistor. In general, the LTM8056 should be used with an output sense resistor to limit the maximum output current, as buck-boost regulators are capable of delivering large cur- rents when the output voltage is lower than the input, if demanded. Furthermore, while the LTM8056 does not require an output sense resistor to operate, it uses information from the sense resistor to optimize its performance. If an out- put sense resistor is not used, the efficiency or output ripple may degrade, especially if the current through the integrated inductor is discontinuous. In some cases, an output sense resistor is required to adequately protect the LTM8056 against output overload or short-circuit. A voltage less than 1.2V applied to the CTL pin reduces the maximum output current if an output current sense resistor is used. Drive CTL to less than about 50mV to stop switching. The current flowing through the sense resistor is reflected by the output voltage of the IOUTMON pin. Driving the SYNC pin will synchronize the LTM8056 to an external clock source. The CLKOUT pin sources a signal that is the same frequency but approximately 180° out of phase with the internal oscillator. If more output current is required than a single LTM8056 can provide, multiple devices may be operated in parallel. Refer to the Parallel Operation section of Applications Information for more details. Aninternalregulatorprovidespowertothecontrolcircuitry and the gate driver to the power MOSFETs. This internal regulator draws power from the SVIN pin. The RUN pin is used to place the LTM8056 in shutdown, disconnecting the output and reducing the input current to less than 1μA. The LTM8056 is equipped with a thermal shutdown that inhibits power switching at high junction temperatures. The activation threshold of this function is above 125°C 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. |
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