Datasheet LTM4602 (Analog Devices) - 8

LTM4602
OPERATION μModule Description
in an overvoltage condition, internal top FET Q1 is turned off and bottom FET Q2 is turned on and held on until the The LTM4602 is a standalone nonisolated synchronous overvoltage condition clears. switching DC/DC power supply. It can deliver up to 6A of DC output current with only bulk external input and output Pulling the RUN/SS pin low forces the controller into its capacitors. This module provides a precisely regulated shutdown state, turning off both Q1 and Q2. Releasing the output voltage programmable via one external resistor from pin allows an internal 1.2μA current source to charge up 0.6VDC to 5.0VDC, not to exceed 80% of the input voltage. the soft-start capacitor. When this voltage reaches 1.5V, The input voltage range is 4.5V to 20V. A simplifi ed block the controller turns on and begins switching. diagram is shown in Figure 1 and the typical application At low load current the module works in continuous cur- schematic is shown in Figure 21. rent mode by default to achieve minimum output voltage The LTM4602 contains an integrated LTC constant on-time ripple. It can be programmed to operate in discontinuous current-mode regulator, ultralow RDS(ON) FETs with fast current mode for improved light load effi ciency when the switching speed and integrated Schottky diode. The typical FCB pin is pulled up above 0.8V and no higher than 6V. switching frequency is 850kHz at full load. With current The FCB pin has a 4.75k resistor to ground, so a resistor mode control and internal feedback loop compensation, to VIN can set the voltage on the FCB pin. the LTM4602 module has suffi cient stability margins and When EXTV good transient performance under a wide range of operat- CC pin is grounded or open, an integrated 5V linear regulator powers the controller and MOSFET gate ing conditions and with a wide range of output capacitors, drivers. If a minimum 4.7V external bias supply is ap- even all ceramic output capacitors (X5R or X7R). plied on the EXTVCC pin, the internal regulator is turned Current mode control provides cycle-by-cycle fast current off, and an internal switch connects EXTVCC to the gate limit. In addition, foldback current limiting is provided in driver voltage. This eliminates the linear regulator power an overcurrent condition while VOSET drops. Also, the loss with high input voltage, reducing the thermal stress LTM4602 has defeatable short-circuit latch off. Internal on the controller. The maximum voltage on EXTVCC pin is overvoltage and undervoltage comparators pull the open- 6V. The EXTVCC voltage should never be higher than the drain PGOOD output low if the output feedback voltage exits VIN voltage. Also EXTVCC must be sequenced after VIN. a ±10% window around the regulation point. Furthermore, 4602fa 8