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LTC2909 Datasheet(PDF) 11 Page - Linear Technology |
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LTC2909 Datasheet(HTML) 11 Page - Linear Technology |
11 / 16 page LTC4365 11 4365f APPLICATIONS INFORMATION The resistor values can then be solved: 1. R1+ R2 = 3mV 10nA = 300k 2. R3 = 2• 3mV 10nA • (3.5V – 0.5V) =1.8M The closest 1% value: R3 = 1.82M: 3. R1 = 300k +1.82M 2 • 18V = 58.9k The closest 1% value: R1 = 59k: R2 = 300k – 59k = 241k The closest 1% value: R2 = 243k Therefore: OV = 17.93V, UV = 3.51V. Reverse VIN Protection The LTC4365’s rugged and hot-swappable VIN input helps protect the more sensitive circuits at the output load. If the input supply is plugged in backwards, or a negative supply is inadvertently connected, the LTC4365 prevents this negative voltage from passing to the output load. The LTC4365 employs a novel, high speed reverse sup- ply voltage monitor. When the negative VIN voltage is detected, an internal switch connects the gates of the external back-to-back N-channel MOSFETs to the nega- tive input supply. As shown in Figure 6, external back-to-back N-channel MOSFETs are required for reverse supply protection. When VIN goes negative, the reverse VIN comparator closes the internal switch, which in turn connects the gates of the external MOSFETs to the negative VIN voltage. The body diode (D1) of M1 turns on, but the body diode (D2) of M2 remains in reverse blocking mode. This means that the common source connection of M1 and M2 remains about a diode drop higher than VIN. Since the gate voltage of M2 is shorted to VIN, M2 will be turned off and no cur- rent can flow from VIN to the load at VOUT. Note that the voltage rating of M2 must withstand the reverse voltage excursion at VIN. Figure 7 illustrates the waveforms that result when VIN is hot plugged to –20V. VIN, GATE and VOUT start out at ground just before the connection is made. Due to the parasitic inductance of the VIN and GATE connections, the voltage at the VIN and GATE pins ring significantly below –20V. Therefore, a 40V N-channel MOSFET was selected to survive the overshoot. The speed of the LTC4365 reverse protection circuits is evident by how closely the GATE pin follows VIN during the negative transients. The two waveforms are almost indistinguishable on the scale shown. Figure 6. Reverse VIN Protection Circuits VIN 4365 F06 VOUT GATE VIN = –40V REVERSE VIN COMPARATOR CLOSES SWITCH WHEN VIN IS NEGATIVE GND LTC4365 M1 D1 D2 M2 + – + TO LOAD COUT Figure 7. Hot Swapping VIN to –20V –20V 5V/DIV GND 4365 F07 500ns/DIV GATE VOUT VIN |
Similar Part No. - LTC2909 |
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Similar Description - LTC2909 |
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