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LTM4639 Datasheet(PDF) 11 Page - Linear Technology |
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LTM4639 Datasheet(HTML) 11 Page - Linear Technology |
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11 / 36 page  LTM4650A-1 11 4650a1f For more information www.linear.com/LTM4650A-1 OPERATION Power Module Description The LTM4650A-1 is a dual-output standalone nonisolated switching mode DC/DC power supply with ±1% total DC output error over line, load and temperature variation. It can provide two 25A outputs or single 50A output with few external input and output capacitors and setup com- ponents. This module provides precisely regulated output voltagesprogrammableviaexternalresistorsfrom0.6VDC to 5.5VDC over 4.5V to 16V input voltages. The typical application schematic is shown in Figure 34. The LTM4650A-1 has dual integrated constant-frequency current mode regulators and built-in power MOSFET devices with fast switching speed. The typical switching frequency is 300kHz to 750kHz depending on different input and output conditions. For switching-noise sensi- tive applications, it can be externally synchronized from 250kHz to 780kHz. A resistor can be used to program a free run frequency on the fSET pin. See the Applications Information section. With current mode control, multi LTM4650A-1s can be easily paralleled to provide up to 300A current with guaranteed perfect current sharing. Also, with current mode control, the LTM4650A-1 module is able to achieve sufficient stability margins and a very fast ±3% output transient response with a minimum number of output capacitors, even with all ceramic output capacitors. This makes LTM4650A-1 the best candidate when powering FPGAs, ASICs and processors in terms of DC accuracy, AC transient response, high output current and accuracy current sharing. See Applications Information section. Current mode control provides cycle-by-cycle fast current limitandfoldbackcurrentlimitinanovercurrentcondition. Internal overvoltage and undervoltage comparators pull the open-drain PGOOD outputs low if the output feedback voltage exits a ±10% window around the regulation point. As the output voltage exceeds 10% above regulation, the bottom MOSFET will turn on to clamp the output voltage. ThetopMOSFETwillbeturnedoff.Thisovervoltageprotect is feedback voltage referred. Pulling the RUN pins below 1.1V forces the regulators into ashutdownstate,byturningoffbothMOSFETs.TheTRACK pinsareusedforprogrammingtheoutputvoltagerampand voltage tracking during start-up or used for soft-starting the regulator. See the Applications Information section. The LTM4650A-1 has a built-in 10pF high frequency filter cap from COMP to SGND for each output. An external RC filtering circuit is required to achieve fast Type II control loop compensation. Table 6 provides a guide line for input, output capacitances and R-C values on COMP pin for several operating conditions. The Linear Technology µModule Power Design Tool (LTpowerCAD®) will be pro- vided for transient and stability analysis. The VFB pin is used to program the output voltage with a single external resistor to ground. A differential remote sense amplifier is available for sensing the output voltage accurately on one of the outputs at the load point, or in parallel operation sensing the output voltage at the load point. High efficiency at light loads can be accomplished with selectable Burst Mode operation or pulse-skipping opera- tion using the MODE_PLLIN pin. These light load features will accommodate battery operation. Efficiency graphs are providedforlightloadoperationintheTypicalPerformance Characteristics section. See the Applications Information section for details. A general purpose temperature diode is included inside the module to monitor the temperature of the module. See the Applications Information section for details. The switch pins are available for functional operation monitoring and a resistor-capacitor snubber circuit can be careful placed on the switch pin to ground to dampen any high frequency ringing on the transition edges. See the Applications Information section for details. |
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