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LTM8047 Datasheet(PDF) 10 Page - Linear Technology |
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LTM8047 Datasheet(HTML) 10 Page - Linear Technology |
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10 / 20 page  LTM8049 10 8049fa For more information www.linear.com/LTM8049 OPERATION The LTM8049 contains two stand-alone switching DC/ DC converters; either one may be configured as a SEPIC (single-ended primary inductance converter) or inverting power supply simply by tying VOUTN or VOUTP to GND, respectively. It accepts an input voltage up to 20VDC. The output is adjustable between 2.5V and 24V for the SEPIC, and between –2.5V and –24V for the inverting configura- tion. The LTM8049 can provide 1.5A at VIN = 12V when VOUT = 5V or –5V at ambient room temperature. As shown in the Block Diagram, the LTM8049 contains a current mode controller, power switching element, power coupled inductor, power Schottky diode and a modest amount of input and output capacitance. The LTM8049 is a fixed frequency PWM regulator. TheLTM8049switchingcanfreerunbyapplyingaresistorto theRTpinorsynchronizetoanexternalsourceatafrequency between 200kHz and 2.5MHz. To synchronize to an external source, drive a valid signal source into the SYNC pin. See SynchronizationintheApplicationsSectionformoredetails. For most applications, the design process is straight forward, summarized as follows: 1. Look at Table 1 and find the row that has the desired input range and output voltage. 2. Apply the recommended CIN,COUT,RADJandRTvalues. While these component combinations have been tested for proper operation, it is incumbent upon the user to verify proper operation over the intended system’s line, load and environmental conditions. Bear in mind that the maximum output current is limited by junction tempera- ture, the relationship between the input and output voltage magnitude and polarity and other factors. Please refer to the graphs in the Typical Performance Characteristics section for guidance. Table 1 gives the recommended component values and configuration for a single channel. Each channel may be configured independently. The maximum frequency (and attendant RT value) at which the LTM8049 should be al- lowed to switch is given in Table 1 in the fMAX column, while the recommended frequency (and RT value) for The LTM8049 also features RUN and SS pins to control the start-up behavior of the device. The RUN pin may also be used to implement an accurate undervoltage lockout function by applying a resistor network to the RUN pin. The LTM8049 features frequency foldback to protect the power switches during a fault or output current overload. During start-up, frequency foldback also limits the current the LTM8049 delivers to the load. The user must evaluate the start-up behavior of the LTM8049 to ensure that it properly powers up the load. The LTM8049 is equipped with a thermal shutdown to protect the device during momentary overload conditions. It is set above the 125°C absolute maximum internal tem- perature rating to avoid interfering with normal specified operation, so internal device temperatures will exceed the absolute maximum rating when the overtemperature protection is active. Therefore, continuous or repeated activation of the thermal shutdown may impair device reliability. optimal efficiency over the given input condition is given in the fOPTIMAL column. Running the LTM8049 faster than the recommended frequency may reduce the usable input voltage range. Capacitor Selection Considerations The CIN and COUT capacitor values in Table 1 are the minimum recommended values for the associated oper- ating conditions. Applying capacitor values below those indicated in Table 1 is not recommended, and may result in undesirable operation. Using larger values is generally acceptable, and can yield improved dynamic response, if it is necessary. Again, it is incumbent upon the user to verify proper operation over the intended system’s line, load and environmental conditions. Ceramic capacitors are small, robust and have very low ESR. However, not all ceramic capacitors are suitable. X5R and X7R types are stable over temperature and ap- plied voltage and give dependable service. Other types, including Y5V and Z5U have very large temperature and voltage coefficients of capacitance. In an application APPLICATIONS INFORMATION |
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