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Hot Swap controller packs MOSFET, sense resistor

Posted: 06 Jul 2010 ?? ?Print Version ?Bookmark and Share

Keywords:Hot Swap controller? MOSFET? sense resistor?

Linear Technology Corp. is rolling out the LTC4219 5A Hot Swap controller for protecting low power boards with load supply voltages ranging from 2.9V to 15V.

The LTC4219 allows a board to be safely inserted and removed from a live backplane by limiting the amount of inrush current to the load supply during power up. Hot Swap controllers typically call for a number of supporting components. However, the LTC4219 integrates a power MOSFET and sense resistor in its power path to limit inrush current, reducing the number of external components required. The device's internal dV/dt circuit means there is no need for an external gate capacitor. An adjustable current limit allows users to vary the current limit threshold under different loading conditions, for example in disk drive spin-up to normal operation. This high level of integration, packaged in a tiny DFN, makes the LTC4219 a convenient Hot Swap solution in space-constrained applications.

The LTC4219 is suitable for a wide range of RAID, server, telecom and industrial applications, especially in compact boards utilizing technologies like Fiber Channel where power is typically limited to less than 25W due to their small size and inability to dissipate large amounts of heat. The LTC4219 was designed with these considerations in mind. During startup, inrush currents are controlled by limiting the gate ramp rate to a safe 0.3V/ms. Load current is monitored using the voltage sensed across the internal 7.5m? sense resistor and adjusting the internal 33m? MOSFET gate-to-source voltage accordingly. A separate ISET pin enables adjustment of the 10 percent accurate (5A) current limit threshold during startup and normal operation as needed. In addition, current foldback and power-good circuitry ensure that the switch is protected from excessive load current and indicate whether or not healthy power conditions are maintained. The LTC4219 also features current, temperature and fault outputs, as well as an adjustable current limit timer.

The LTC4219 is available as a dedicated 12V (LTC4219-12) or 5V (LTC4219-5) version, which contain preset 12V/5V-specific thresholds. Both devices are offered in commercial and industrial operating temperature grades. The LTC4219 is available in a small, RoHS-compliant, 16-pin 5mm x 3mm DFN package and priced starting at $3.35 each in 1,000-piece quantities.

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