Datasheet LTM4657 (Analog Devices) - 9

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OPERATION
The LTM4657 is a standalone nonisolated switch mode OV and UV condition except during start-up when the DC/DC power supply. It can deliver up to 8A DC output TRACK pin is ramping up to 0.5V. current with few external input and output capacitors. Furthermore, in order to protect the internal power This module provides precisely regulated output voltage MOSFET devices against transient voltage spikes, the adjustable between 0.5V to 5.5V via one external resistor LTM4657 constantly monitors the V over a 3.1V to 20V input voltage range. The typical appli- IN pin for an overvolt- age condition. When V cation schematic is shown in Figure 23. IN rises above 24.5V, the regulator suspends operation by shutting off both power MOSFETs. The LTM4657 contains an integrated constant on-time Once VIN drops below 21.5V, the regulator immediately valley current mode regulator, power MOSFETs, inductor, resumes normal operation. The regulator does not exe- and other supporting discrete components. The default cute its soft-start function when exiting an overvoltage switching frequency is 500kHz. For switching noise- condition. sensitive applications, the switching frequency can be Multiphase operation can be easily employed with the adjusted by external resistors and the μModule regulator synchronization and phase mode controls. Up to 6 phases can be externally synchronized to a clock within ±30% can be cascaded to run simultaneously with respect to of the set frequency. See the Applications Information each other by programming the PHMODE pin to different section. levels. The LTM4657 has MODE/CLKIN and CLKOUT pins With current mode control and internal feedback loop for PolyPhase operation of multiple devices or frequency compensation, the LTM4657 module has sufficient sta- synchronization. bility margins and good transient performance with a wide Pulling the RUN pin to GND forces the controller into its range of output capacitors, even with all ceramic output shutdown state, turning off both power MOSFETs and capacitors. most of the internal control circuitry. At light load currents, Current mode control provides cycle-by-cycle fast current discontinuous mode (DCM) operation can be enabled to limiting. Internal output overvoltage and undervoltage achieve higher efficiency compared to continuous mode comparators pull the open-drain PGOOD output low if the (CCM) by pul ing the MODE/CLKIN pin to GND. The output feedback voltage exits a ±8% window around the TRACK/SS pin is used for power supply tracking and regulation point. Continuous operation is forced during soft-start programming. See the Applications Information section. Rev 0 For more information www.analog.com 9 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Electrical Characteristics Pin Configuration Typical Performance Characteristics Pin Functions Block Diagram Decoupling Requirements Operation Applications Information Package Description Package Photo Design Resources Related Parts