DEMO MANUAL DC1850A-A/DC1850A-B LTC4366HTS8-1/LTC4366HTS8-2 Very High Voltage Surge Stopper Description Demonstration Circuit 1850A showcases the LTC 4366 DC1850A-A features latchoff behavior after a fault and is high voltage surge stopper in a 28V vehicular application. reset by asserting the SHUTDOWN input high for at least DC1850A withstands inputs of up to 100VDC and input 100s. DC1850A-B features auto-retry 9 seconds after transients of up to 250V while maintaining the output at tripping off in an overvoltage fault condition. The 9 second 43.1V. Reverse battery and errant inputs of up to 100VDC delay can be interrupted by pulsing the SHUTDOWN input. are blocked from reaching the output. Design files for this circuit board are available at DEMO MANUAL DC1850A-A/DC1850A-B o The LTC4366 surge stopper operates in a floating topol- 100V Reverse Voltage Protection Circuit ogy, permitting the design of circuits capable of operating Reverse polarity inputs of up to 100V are blocked from at virtually unlimited input voltage. DC1850A has been reaching the load by M2, whose associated circuitry is designed to protect against 100VDC and 250V for 1ms, located on the bottom of the board. This circuit blocks in 28V vehicle applications. The input start-up range is reverse inputs of up to 250VDC, provided the input is 18V to 41V, while after start-up the input can fall to ap- applied from a cold start. If DC1850A is already on and proximately 7V while still passing 1.5A load current. operating with a positive input voltage, instantaneous Careful attention has been paid to the layout to provide at spikes must not exceed 100V. least 87mil (2.2mm) clearance between input and output, and input and ground. This wide clearance is capable of SHUTDOWN TURRET withstanding 100VDC and spikes to 250V without arcing. If the SHUTDOWN turret is left open, DC1850A defaults The operating ranges are shown in silkscreen on the top to the ON state and turns on when an input supply is of the board. The bottom shows the U1 part number, top connected. Pulling SHUTDOWN to 1.8V or higher causes mark and behavior associated with the A and B ver- the LTC4366 to enter its shutdown state. The circuit sions of DC1850A. This same information is shown on board layout limits the maximum SHUTDOWN voltage to the schematic. 60VDC, while R2 limits the peak applied transient voltage capability to 100V. Three ancillary circuits are located on the bottom of the board. OPTIONAL COMPONENTS Shutdown Level Shifter Two optional components, CX and RX are made available Since the LTC4366 operates in a floating topology, it is for those who wish to experiment with the frequency necessary to level shift ground-referred shutdown signal- response of the overvoltage regulation loop. ling. A simple NPN circuit provides level shifting between the SHUTDOWN turret and the LTC4366s SD pin. HOW TO OPERATE DC1850A Wide Voltage Range Constant Current LED Driver Operation of DC1850A is straightforward: connect an input supply of 18V to 41V, and an output load of up to Making an LED operate at constant brightness over a 1.5A. If the SHUTDOWN turret is open circuit the output wide operating range is made possible by a simple, two- will power up. If the input voltage is increased above transistor circuit. Input LED (D6) current is held constant 43.1V, the output will limit and shut off after 2.8ms. DC from 18V to 250V, and emits some light as low as 7V. inputs of up to 100V may be applied. The basic hookup Output LED (D5) is biased with a 9.1k resistor (R7, on bot- is shown in Figure 1. tom of board). Its brightness will vary with output voltage. dc1850aabf 2 verview