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LTC4210-1 Datasheet(PDF) 8 Page - Linear Technology |
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LTC4210-1 Datasheet(HTML) 8 Page - Linear Technology |
8 / 20 page 8 LTC4210-1/LTC4210-2 421012f APPLICATIO S I FOR ATIO Hot Circuit Insertion When circuit boards are inserted into live backplanes, the supply bypass capacitors can draw large transient cur- rents from the backplane power bus as they charge. Such transient currents can cause permanent damage to con- nector pins, glitches on the system supply or reset other boards in the system. The LTC4210 is designed to turn a printed circuit board’s supply voltage ON and OFF in a controlled manner, allow- ing the circuit board to be safely inserted into or removed from a live backplane. The LTC4210 can reside either on the backplane or on the daughter board for hot circuit insertion applications. Overview The LTC4210 is designed to operate over a range of supplies from 2.7V to 16.5V. Upon insertion, an undervolt- age lockout circuit determines if sufficient supply voltage is present. When the ON pin goes high an initial timing cycle assures that the board is fully seated in the backplane before the MOSFET is turned on. A single timer capacitor sets the periods for all of the timer functions. After the initial timing cycle the LTC4210 can either start up in current limit or with a lower load current. Once the external MOSFET is fully enhanced and the supply has ramped up, the LTC4210 monitors the load current through an exter- nal sense resistor. Overcurrent faults are actively limited to 50mV/RSENSE for a specified circuit breaker timer limit. The LTC4210-1 will automatically retry after a current limit fault while the LTC4210-2 latches off. The LTC4210-1 timer function limits the retry duty cycle to 3.8% for MOSFET cooling. Undervoltage Lockout An internal undervoltage lockout (UVLO) circuit resets the LTC4210 if the VCC supply is too low for normal operation. The UVLO has a low-to-high threshold of 2.5V, a 100mV hysteresis and a high-to-low glitch filter of 30 µs. Above 2.5V supply voltage, the LTC4210 will start if the ON pin conditions are met. A short supply dip below 2.4V for less than 30 µs is ignored to allow for bus supply transients. ON Function The ON pin is the input to a comparator which has a low- to-high threshold of 1.3V, an 80mV hysteresis and a high- to-low glitch filter of 30 µs. A low input on the ON pin resets the LTC4210 TIMER status and turns off the external MOSFET by pulling the GATE pin to ground. A low-to-high transition on the ON pin starts an initial cycle followed by a start-up cycle. A 10k pull-up resistor connecting the ON pin to the supply is recommended. The 10k resistor shunts any potential static charge on the backplane and reduces the overvoltage stress at the ON pin during live insertion. Alternatively, an external resistor divider at the ON pin can be used to program an undervoltage lockout value higher than the internal UVLO circuit. An RC filter can be added at the ON pin to increase the delay time at card insertion if the internal glitch filter delay is insufficient. GATE Function During hot insertion of the PCB, an abrupt application of supply voltage charges the external MOSFET drain/gate capacitance. This can cause an unwanted gate voltage spike. An internal proprietary circuit holds GATE low before the internal circuitry wakes up. This reduces the MOSFET current surges substantially at insertion. The GATE pin is held low in reset mode and during the initial timing cycle. In the start-up cycle the GATE pin is pulled up by a 10 µA current source. During an overcurrent fault condition, the error amplifier servoes the GATE pin to maintain a constant current to the load until the circuit breaker trips. When the circuit breaker trips, the GATE pin shuts down abruptly. |
Similar Part No. - LTC4210-1 |
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Similar Description - LTC4210-1 |
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