link to page 10 link to page 10 link to page 10 LTC4368 APPLICATIONS INFORMATION +50mV M1 M2 V PSMN4R8-100BSE SiR662 0.004Ω V IN OUT 24V 7V TO 36V INRUSH –0.75A TO 12.5A CONTROL –3mV 22k 2.2nF GATE SENSE VOUT VIN R4 464k SHDN R3 OV = 36V 1500k LTC4368-2 UV = 7V UV FAULT 1200ms COOLDOWN R2 AFTER FORWARD 121k OC FAULT OV RETRY R1 GND 0.22µF 29.4k 4368 F02 Figure 2. LTC4368-2 Protects Load from Voltage (–40V to 100V) and Current (–0.75A to 12.5A) Faults The LTC4368 is an N-channel MOSFET controller that pro- GATE Drive tects a load from overvoltage faults (both positive and The LTC4368 turns on the external N-channel MOSFETs negative) and from overcurrent faults (both forward and by driving the GATE pin above V reverse). A typical application circuit using the LTC4368-2 OUT. The voltage differ- ence between the GATE and V is shown in Figure 2. The circuit provides a low loss con- OUT pins (gate drive) is a function of V nection from V IN and VOUT. IN to VOUT as long as there are no voltage or current faults. Figure 3 highlights the dependence of the gate drive on V Voltages at V IN and VOUT. When system power is first turned on IN outside of the 7V to 36V range are (SHDN low to high, SENSE = V prevented from getting to the load and can be as high as OUT = 0V), gate drive is at a maximum for all values of V 100V and as negative as –40V. Load currents (including IN. This helps prevent startup problems into heavy loads by ensuring that there inrush currents) above 12.5A (forward from VIN to VOUT) is enough gate drive to support the load. and below –0.75A (reverse from VOUT to VIN) will cause the load to be disconnected from V 14 IN. The circuit of Figure 2 TA = 25°C protects against negative voltages at V I IN as shown. Note 12 GATE = –1µA VIN = 12V, 60V that the SOA and voltage requirements are not the same 10 for the two external MOSFETs. During power-up, the input MOSFET (M1) will stand off more voltage (up to VIN) than (V) 8 VIN = 5V the output MOSFET (M2). The body diode of M2 will limit GATE∆V 6 V its drain to source voltage. This allows the use of smaller IN = 3.3V 4 MOSFETs at the output. VIN = 2.5V 2 During normal operation, the LTC4368 provides up to 13.1V of gate enhancement to the external back-to-back 0 0 5 10 15 N-channel MOSFETs. This turns on the MOSFETs, thus VOUT (V) 4365 F03 connecting the load at VOUT to the supply at VIN. Figure 3. Gate Drive (GATE – VOUT) vs VOUT Rev. B 10 For more information www.analog.com Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Pin Functions Block Diagram Applications Information Related Parts Features Applications Typical Application Description Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Pin Functions Block Diagram Operation Applications Information Package Description Revision History Typical Application Related Parts
