FET-based surge stopper gives transient protection for 8 microAmp Iq

April 26, 2016 // By Graham Prophet
LTC4380 is an ultralow quiescent current (IQ) surge stopper, providing compact overvoltage and overcurrent protection for always-on 4V to 72V electronics in automotive, industrial and avionic systems.

The device replaces traditional shunt circuits composed of inductors, capacitors, transient voltage suppressors (TVS), and fuses with a simple IC and series N-channel MOSFET solution, saving board space and enabling continuous operation through transient voltage or current surges. The LTC4380 protects downstream electronics from input overvoltage up to the MOSFET rating, while also protecting the power supply from output overload. Device current consumption is 8 µA in normal operation and 6 µA in shutdown mode, prolonging battery run and standby time. The low current allows a large filtering resistor to the device supply pin, enabling operation through automotive cold crank and overvoltage transients above 100V.

 

During an input voltage surge, such as automotive load dump, the LTC4380 drops the excess voltage across the external MOSFET while clamping its gate and therefore the output to a safe voltage. This enables the use of lower voltage rated electronics downstream, saving costs. The clamp voltage is pin-selectable for 12V and 24V systems, or adjustable with an input Zener diode. During an output overload or short-circuit, the LTC4380 regulates the forward path to a current limit set by a sense resistor. For sustained overvoltage or overcurrent conditions, a MOSFET stress-accelerated timeout ensures safe turn-off of the MOSFET. In contrast, traditional protection circuits may blow a fuse or burn out the TVS.

 

The LTC4380 withstands a reversed input, such as an incorrectly inserted battery, to -60V. Adjustable input undervoltage lockout threshold blocks start-up for out-of-range voltages, avoiding deeply discharged batteries. The device also controls inrush current during hot plug of a circuit board’s power supply.

 

The LTC4380 is available in four options: the LTC4380-1 and LTC4380-2 have a pin-selectable clamp voltage, whereas the LTC4380-3 and LTC4380-4 clamp voltage is set with an input Zener diode. After a fault, the LTC4380-1 and LTC4380-3 latch the MOSFET off, while the LTC4380-2 and LTC4380-4 automatically turn on with a 0.1% duty cycle. Specified over the