Datasheet LTC4364-1, LTC4364-2 (Analog Devices) - 10

LTC4364-1/LTC4364-2
OPERATION
The LTC4364 is designed to suppress high voltage surges to help keep the MOSFET within its safe operating area and limit the output voltage to protect load circuitry and (SOA). The LTC4364-1 latches off M1 and keeps FLT low ensure normal operation in high availability power systems. after a fault timeout. The LTC4364-2 allows M1 to turn It features an overvoltage protection regulator that drives back on and FLT to go high impedance after a cool down an external N-channel MOSFET (M1) as the pass device timer cycle, provided the OV pin is below its threshold. and an ideal diode controller that drives a second external After the HGATE pin is latched low following fault, mo- N-channel MOSFET (M2) for reverse input protection and mentarily pulling the SHDN pin below 0.5V resets the fault output voltage holdup. and allows HGATE to pull high for both LTC4364-1 and The LTC4364 operates from a wide range of supply voltage, LTC4364-2. In addition, momentarily pulling the UV pin from 4V to 80V. With a clamp limiting the VCC supply, the below 0.6V allows HGATE to pull high after the cool down input voltage may be higher than 80V. The input supply timer delay for LTC4364-1, but has no effect on LTC4364-2. can also be pulled below ground potential by up to 40V The source and drain of MOSFET M2 serve as the anode without damaging the LTC4364. The low power supply and cathode of the ideal diode. The LTC4364 controls the requirement of 4V allows it to operate even during cold DGATE pin to maintain a 30mV forward voltage across the cranking conditions in automotive applications. drain and source terminals of M2. It reduces the power Normally, the pass device M1 is fully on, supplying current dissipation and increases the available supply voltage to to the load with very little power loss. If the input voltage the load, as compared to using a discrete blocking diode. surges too high, the voltage amplifier (VA) controls the gate If M2 is driven fully on and the load current results in of M1 and regulates the voltage at the OUT pin to a level more than 30mV of forward voltage, the forward voltage that is set by an external resistive divider from the OUT pin is equal to RDS(ON) • ILOAD. to ground and the internal 1.25V reference. The LTC4364 In the event of an input short or a power supply failure, also detects an overcurrent condition by monitoring the reverse current temporarily flows through the MOSFET voltage across an external sense resistor placed between M2 that is on. If the reverse voltage exceeds –30mV, the the SENSE and OUT pins. An active current limit circuit LTC4364 pulls the DGATE pin low strongly and turns off (IA) controls the gate of M1 to limit the sense voltage to M2, minimizing the disturbance at the output. 50mV if OUT is above 2.5V. In the case of a severe output short that brings OUT below 1.5V, the sense voltage is If the input supply drops below the GND pin voltage, the reduced to 25mV to reduce the stress on M1. DGATE pin is pulled to the SOURCE pin voltage, keeping M2 off. When the HGATE pin pulls low in any fault condi- During an overvoltage or overcurrent event, a current tion, the DGATE pin also pulls low, so both pass devices source starts charging up the capacitor connected at are turned off. the TMR pin to ground. The pull-up current source in overcurrent condition is 5 times of that in overvoltage to If the output (and so the SOURCE pin, through the body accelerate turn-off. When TMR reaches 1.25V, the FLT pin diode of M2) drops below GND, the HGATE pin is pulled pulls low to warn of impending turn-off. The pass device to the SOURCE pin voltage, turning M1 off and shutting M1 stays on and the TMR pin is further charged up until it down the forward current path. reaches 1.35V, at which point the HGATE pin pulls low and An input undervoltage condition is accurately detected turns off M1. The fault timer allows the load to continue using the UV pin. The HGATE and DGATE pins remain low functioning during brief transient events while protecting if UV is below its 1.25V threshold. The SHDN pin not only the MOSFET from being damaged by a long period of input turns off the pass devices but also shuts down the internal overvoltage, such as load dump in vehicles. The fault timer circuitry, reducing the supply current to 10µA. period decreases with the voltage across the MOSFET, 436412f 10 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Applications Package Description Typical Application Related Parts