Datasheet LTM4600 (Analog Devices) - 9

LTM4600
operaTion µModule Description
a ±10% window around the regulation point. Furthermore, The LTM4600 is a standalone non-isolated synchronous in an overvoltage condition, internal top FET Q1 is turned switching DC/DC power supply. It can deliver up to 10A of off and bottom FET Q2 is turned on and held on until the DC output current with only bulk external input and output overvoltage condition clears. capacitors. This module provides a precisely regulated Pulling the RUN/SS pin low forces the controller into its output voltage programmable via one external resistor from shutdown state, turning off both Q1 and Q2. Releasing the 0.6VDC to 5.0VDC, not to exceed 80% of the input voltage. pin allows an internal 1.2µA current source to charge up The input voltage range is 4.5V to 20V. A simplified block the soft-start capacitor. When this voltage reaches 1.5V, diagram is shown in Figure 1 and the typical application the controller turns on and begins switching. schematic is shown in Figure 18. At low load current the module works in continuous cur- The LTM4600 contains an integrated LTC constant on-time rent mode by default to achieve minimum output voltage current-mode regulator, ultra-low RDS(ON) FETs with fast ripple. It can be programmed to operate in discontinuous switching speed and integrated Schottky diode. The typical current mode for improved light load efficiency when the switching frequency is 850kHz at full load. With current FCB pin is pulled up above 0.8V and no higher than 6V. mode control and internal feedback loop compensation, The FCB pin has a 4.75k resistor to ground, so a resistor the LTM4600 module has sufficient stability margins and to VIN can set the voltage on the FCB pin. good transient performance under a wide range of operat- When EXTV ing conditions and with a wide range of output capacitors, CC pin is grounded or open, an integrated 5V linear regulator powers the controller and MOSFET gate even all ceramic output capacitors (X5R or X7R). drivers. If a minimum 4.7V external bias supply is ap- Current mode control provides cycle-by-cycle fast current plied on the EXTVCC pin, the internal regulator is turned limit. In addition, foldback current limiting is provided in off, and an internal switch connects EXTVCC to the gate an over-current condition while VOSET drops. Also, the driver voltage. This eliminates the linear regulator power LTM4600 has defeatable short circuit latch off. Internal loss with high input voltage, reducing the thermal stress overvoltage and undervoltage comparators pull the open- on the controller. The maximum voltage on EXTVCC pin is drain PGOOD output low if the output feedback voltage exits 6V. The EXTVCC voltage should never be higher than the VIN voltage. Also EXTVCC must be sequenced after VIN. 4600fd For more information www.linear.com/LTM4600 9 Document Outline Features Applications Typical Application Description Absolute Maximum Ratings Order Information Pin Configuration Electrical Characteristics Typical Performance Characteristics Pin Functions Simplified Block Diagram Decoupling Requirements Operation Applications Information Typical Application Package Description Revision History Typical Application Related Parts