Datasheet LTM4638 (Analog Devices) - 10

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OPERATION
The LTM4638 is a standalone nonisolated switch mode Furthermore, in order to protect the internal power MOSFET DC/DC power supply. It can deliver up to 15A DC output devices against transient voltage spikes, the LTM4638 current with few external input and output capacitors. constantly monitors the VIN pin for an overvoltage condi- This module provides precisely regulated output voltage tion. When VIN rises above 24.5V, the regulator suspends adjustable between 0.6V to 5.5V via one external resistor operation by shutting off both power MOSFETs. Once VIN over a 3.1V to 20V input voltage range. The typical ap- drops below 21.5V, the regulator immediately resumes plication schematic is shown in Figure 23. normal operation. The regulator does not execute its The LTM4638 contains an integrated constant on-time soft-start function when exiting an overvoltage condition. valley current mode regulator, power MOSFETs, inductor, Multiphase operation can be easily employed with the and other supporting discrete components. The default synchronization and phase mode controls. Up to 6 phases switching frequency is 600kHz. For switching noise- can be cascaded to run simultaneously with respect to sensitive applications, the switching frequency can be each other by programming the PHMODE pin to different adjusted by external resistors and the μModule regulator levels. The LTM4638 has MODE/CLKIN and CLKOUT pins can be externally synchronized to a clock within ±30% of for PolyPhase operation of multiple devices or frequency the set frequency. See the Applications Information section. synchronization. With current mode control and internal feedback loop Pulling the RUN pin to GND forces the controller into its compensation, the LTM4638 module has sufficient stabil- shutdown state, turning off both power MOSFETs and ity margins and good transient performance with a wide most of the internal control circuitry. At light load currents, range of output capacitors, even with all ceramic output discontinuous mode (DCM) operation can be enabled to capacitors. achieve higher efficiency compared to continuous mode Current mode control provides cycle-by-cycle fast current (CCM) by pulling the MODE/CLKIN pin to GND. The limiting. Internal output overvoltage and undervoltage TRACK/SS pin is used for power supply tracking and comparators pull the open-drain PGOOD output low if the soft-start programming. See the Applications Informa- output feedback voltage exits a ±8% window around the tion section. regulation point. Continuous operation is forced during OV and UV condition except during start-up when the TRACK pin is ramping up to 0.6V. Rev. B 10 For more information www.analog.com Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Decoupling Requirements Operation Applications Information Package Description Revision History Package Photo Related Parts