Linear LT4356-3 High Voltage Transient Load Protection Solution

Limiting the output to a safe value. The LT4356-3 also monitors the voltage drop across the VCC and 蔼SNS pins to protect the overcurrent driver. The LT4356-3 operates from 4V to 80V with reverse input protection to -60V. The shutdown pin can withstand voltages from -60V to 100V and shutdown currents of only 7uA, which can be used for surge protection, hot swap, and intrinsically safe applications in automotive and military aircraft. This article describes the main features of the LT4356-3, block diagram , a variety of protection application circuits and circuit diagrams of the DC1018 evaluation board.

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The LT4356-3 surge stopper protects loads from high voltage transients. It regulates the output during an overvoltage event, such as load dump in automobiles, by controlling the gate of an external N-channel MOSFET.

The output is limited to a safe value such allowing the loads to continue functioning. The LT4356-3 also monitors the voltage drop between the VCC and SNS pins to protect against overcurrent faults. An internal amplifier limits the current sense voltage to 50mV. Fault condition, a timer is started inversely proportional to MOSFET stress. If the timer expires, the FLT pin pulls low to warn of an impending power down. If the condition persists, the MOSFET is turned off, until the SHDN pin pulls low momentarily.

The spare amplifier may be used as a voltage detection comparator or as a linear regulator controller driving an external PNP pass transistor. Back-to-back FETs can be used in lieu of a Schottky diode for reverse input protection, reducing voltage drop and power loss A shutdown pin reduces the quiescent current to less than 7μA during shutdown.

Main features of LT4356-3:

Stops High Voltage Surges

Adjustable Output Clamp Voltage

Overcurrent Protection

Wide Operation Range: 4V to 80V

Reverse Input Protection to –60V

Low 7μA Shutdown Current

Adjustable Latchoff Fault Timer

Controls N-channel MOSFET

Shutdown Pin Withstands –60V to 100V

Fault Output Indication

Spare Amplifi er for Level Detection Comparator or

Linear Regulator Controller

Available in (4mm 3mm) 12-Pin DFN, 10-Pin MSOP or 16-Pin SO Packages

LT4356-3 application:

Automotive/Avionic Surge Protection

Hot Swap/Live Insertion

High Side Switch for Battery Powered Systems

Intrinsic Safety Applications


Figure 1. Block diagram of the LT4356-3


Figure 2. Overvoltage regulator circuit diagram with N-MOSFET inverting input protection


Figure 3. Overvoltage regulator circuit diagram with P-MOSFET inverting input protection


Figure 4. Voltage regulator circuit diagram with low battery detection


Figure 5. Vin can withstand a 150V 24V overvoltage regulator circuit diagram


Figure 6. Overvoltage regulator circuit diagram with low battery detection and output still working when turned off


Figure 7. 2.5A 48V Hot Swap Circuit Diagram with Overvoltage Output Regulator (72V)


Figure 8. 2.5A 48V Hot Swap Circuit Diagram with Overvoltage Output Regulator (36V)


Figure 9. Overvoltage regulator with reverse input protection up to -80V

DC1018 - LT4356-1 Evaluation Kit

Demonstration Circuit DC-1018A showcases the LT4356 Surge Stopper in a 12V, 3A application. Input transients of up to 60V are limited to 16V at the output; sustained overvoltage conditions cause the limiter to trip off and retry after the overvoltage is removed.


Figure 10. DC1018 Evaluation Board Circuit Diagram

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