Datasheet LTC4367 (Analog Devices) - 10

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APPLICATIONS INFORMATION
The LTC4367 is an N-channel MOSFET controller that
GATE Drive
protects a load from faulty supply connections. A basic The LTC4367 turns on the external N-channel MOSFETs by application circuit using the LTC4367 is shown in Figure 2 driving the GATE pin above V The circuit provides a low loss connection from V OUT. The voltage difference IN to between the GATE and V V OUT pins (gate drive) is a function OUT as long as the voltage at VIN is between 3.5V and of V 18V. Voltages at V IN and VOUT. IN outside of the 3.5V to 18V range are prevented from getting to the load and can be as high as Figure 3 highlights the dependence of the gate drive on VIN 100V and as low as –40V. The circuit of Figure 2 protects and VOUT. When system power is first turned on (SHDN against negative voltages at VIN as shown. No other external low to high, VOUT = 0V), gate drive is at a maximum for all components are needed. values of VIN. This helps prevent start-up problems into heavy loads by ensuring that there is enough gate drive During normal operation, the LTC4367 provides up to to support the load. 13.1V of gate enhancement to the external back-to-back N-channel MOSFETs. This turns on the MOSFETs, thus As VOUT ramps up from 0V, the absolute value of the GATE connecting the load at VOUT to the supply at VIN. voltage remains fixed until VOUT is greater than the lower of (VIN – 1V) or 5V. Once VOUT crosses this threshold, gate drive begins to increase up to a maximum of 13.1V Si7942 100V DUAL (for VIN ≥ 12V). The curves of Figure 3 were taken with VIN VOUT 12V NOMINAL 3.5V TO 18V a GATE load of –1µA. If there were no load on GATE, the M1 M2 + COUT 100µF gate drive for each VIN would be slightly higher. GATE Note that when V V VOUT IN is at the lower end of the operating IN LTC4367 R4 range, the external N-channel MOSFET must be selected 453k with a corresponding lower threshold voltage. SHDN R3 1370k 14 TA = 25°C UV FAULT I 12 GATE = –1µA R2 243k OV = 18V 10 VIN = 60V OV UV = 3.5V VIN = 12V R1 GND 59k (V) 8 4367 F02 VIN = 5V GATE∆V 6 VIN = 3.3V
Figure 2. LTC4367 Protects Load from –40V
4 VIN = 2.5V
to 100V VIN Faults
2 0 0 5 10 15 VOUT (V) 4367 F03
Figure 3. Gate Drive (GATE – VOUT) vs VOUT
4367fb 10 For more information www.linear.com/LTC4367