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LTC4223CDHD-2PBF Datasheet(PDF) 9 Page - Linear Technology |
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LTC4223CDHD-2PBF Datasheet(HTML) 9 Page - Linear Technology |
9 / 24 page LTC4223-1/LTC4223-2 9 422312f OPERATION The LTC4223 is designed to control the power on an Ad- vanced Mezzanine Card (AMC) or MicroTCA backplane, allowing boards to be safely inserted and removed. It controls the 12V main and 3.3V auxiliary power through an external N-channel MOSFET and integrated pass transistor. These two supplies can be turned on and off independently by their respective ON control pins. If either AUXON or 12ON is pulled high, an initial tim- ing cycle set by the TIMER capacitor value is initiated once all these conditions are met: input supplies out of undervoltage lockout; TIMER < 0.2V and ⎯E⎯N low. At the end of the initial timing cycle, if the AUXON pin is high, the internal pass transistor turns on. It enters into an active current limit loop if the inrush current charging the load capacitor exceeds 240mA. When the load is in current limit, a 10μA pull-up charges the TIMER pin capacitor. If the load capacitor is fully charged and the switch is no longer in current limit before the TIMER reaches 1.235V, ⎯A⎯U⎯X⎯P⎯G⎯O⎯O⎯D pulls low indicating that power is good. Otherwise the internal switch turns off and ⎯F⎯A⎯U⎯L⎯T pulls low when TIMER reaches 1.235V. If 12ON pin is high at the end of the initial timing cycle, an internal charge pump charges the gate of the external MOSFET with 10μA pull-up. Connecting an external gate capacitor limits the inrush current charging the load ca- pacitor. If the inrush current exceeds its limited current value, an internal analog current limit (ACL) amplifier servos the gate to force 60mV across the external sense resistor connected between 12VIN and 12VSENSE pins. During this period, TIMER pin capacitor is charged by a 200μA pull-up. If the load is fully charged and no longer in current limit before the TIMER reaches 1.235V, ⎯1⎯2⎯P⎯G⎯O⎯O⎯D pulls low. Otherwise 12V shuts off and ⎯F⎯A⎯U⎯L⎯T pulls low when TIMER reaches 1.235V. If an overcurrent fault occurs on the auxiliary supply after power-up, the current is limited to 240mA and after a 25μs delay, the circuit breaker trips and ⎯F⎯A⎯U⎯L⎯T pulls low. Ther- mal shutdown protects the internal pass transistor from overheating by shutting it off at 150°C. If an overcurrent fault occurs on the 12V supply, the current is limited to 60mV/RSENSE. After a timing cycle delay set by 200μA charging the TIMER capacitor, the circuit breaker trips and ⎯F⎯A⎯U⎯L⎯T pulls low. An overcurrent fault on the auxiliary supply shuts off 12V; a fault on the 12V supply does not affect the auxiliary supply. The LTC4223 provides high side current sensing informa- tion for the 12V supply at the 12IMON pin. The 12IMON output voltage is 33 times the sense voltage, allowing it to be used with an external ADC. In the off condition, 12VOUT and AUXOUT are discharged to ground by internal N-channel pull downs. |
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