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LTC3880 Datasheet(PDF) 11 Page - Linear Technology |
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LTC3880 Datasheet(HTML) 11 Page - Linear Technology |
11 / 28 page LTM8001 11 8001f For more information www.linear.com/8001 OPERATION The LTM8001 consists of two major parts: the first is a standalonenonisolatedstep-downswitchingDC/DCpower converter that can deliver up to 5A of output current. The second part is an array of five parallelable 1.1A LDOs. The DC/DC converter provides a precisely regulated output voltage programmable via one external resistor from 1.2V to 24V. The input voltage range is 6V to 36V. Given that it is a step-down converter, make sure that the input volt- age is high enough to support the desired output voltage and load current. The linear regulator array consists of five low drop-out regulators, of which three inputs are dedicated to the buck converter’s output (VOUT0) and two tie to an undedicated input (VIN45). Each individual linear regulator may be set to a unique voltage through its SET pin, or may be paralleled with other LDOs by tying their respective SET and VOUT pins together. TheLTM8001step-downswitchingconverterutilizesfixed frequency, average current mode control to accurately regulate the output current. This results in a constant- voltage, constant-current output characteristic, making the LTM8001’s step-down regulator well suited for many supercapacitorandbatterychargingapplications.Asshown intheTypicalPerformanceCharacteristics,thecurrentlimit works in both directions. The control loop will regulate the current in the internal inductor. Once the VOUT0 output has reached the regulation voltage determined by the resistor fromtheFBOpintoground,thevoltageregulationloopwill reduce the output current and maintain the output voltage. The ILIM input may be used to set the maximum allowable current output of the LTM8001. The analog control range of the ILIM pin is from 0V to 1.5V. If the ILIM pin is raised above 1.5V, there is little or no effect. The RUN pin functions as a precision enable for the step- down switching converter connected to VOUT0. As the VOUT1-3 LDO inputs are tied to VOUT0, the RUN pin will also implicitly enable or disable these LDOs as well, unless some external power source is tied to VOUT0. Refer to the ApplicationsInformationsectionShortedInputProtection if VOUT0 is forced above VIN0. When the voltage at the RUN pin is lower than 1.55V, switching is terminated. Below the turn-on threshold, the RUN pin sinks 5.5μA. This current can be used with a resistor between RUN and VIN0 to set hysteresis.PleaserefertotheUVLOandShutdownsection in the Applications Information for further details. During start-up, the SS pin is held low until the part is enabled, after which the capacitor at the soft-start pin is charged with an 11μA current source. The LTM8001 is equipped with thermal shutdown circuitry to protect the device during momentary overload condi- tions. It is set above the 125°C absolute maximum internal temperature rating to avoid interfering with normal speci- fied operation, so internal device temperatures will exceed the absolute maximum rating when the overtemperature protection is active. Thus, continuous or repeated activa- tion of the thermal shutdown may impair device reliability. During thermal shutdown, all switching is terminated and the SS pin is driven low. The switching frequency is determined by a resistor at the RT pin. The LTM8001 may also be synchronized to an external clock through the use of the SYNC pin. Please see the Switching Frequency Synchronization section in the Applications Information for further details. The VOUT1-5 linear regulators are easy to use and have all the protection features expected in high performance regulators. Included are short-circuit protection and safe operating area protection, as well as thermal shutdown. These linear regulators are especially well suited to ap- plications needing multiple rails. Their architecture allows their outputs to be adjusted down to zero volts. The output voltage is set by a single resistor, handling modern low voltage digital ICs as well as allowing easy parallel opera- tion and simplified thermal management. The linear regulators can be operated in two modes. One mode has the BIAS123 and BIAS45 pins connected to the linear regulator power input pins (VOUT0 and VIN45) which givesalimitationofabout1.6Vdropout.Intheothermode, the BIAS123 and BIAS45 pins can be tied to a voltage at least1.6Vabovetheirhighestrespectiveoutputs.Thelinear regulator power input (VOUT0 and VOUT45) can then be set to a lower voltage that meets the dropout requirement, minimizing the power dissipation. |
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Similar Description - LTC3880 |
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