Negative Voltage Hot Swap Controllers

The LTC4252 negative voltage Hot Swap™ controller allows a board to be safely inserted and removed from a live backplane. Output current is controlled by three stages of current limiting: a timed circuit breaker, active current limiting and a fast feedforward path that limits peak current under worst-case catastrophic fault conditions.

Adjustable undervoltage and overvoltage detectors disconnect the load whenever the input supply exceeds the desired operating range. The LTC4252’s supply input is shunt regulated, allowing safe operation with very high supply voltages. A multifunction timer delays initial startup and controls the circuit breaker’s response time. The circuit breaker’s response time is accelerated by sensing excessive MOSFET drain voltage, keeping the MOSFET within its safe operating area (SOA). An adjustable softstart circuit controls MOSFET inrush current at start-up.

The LTC4252-1/LTC4252A-1 latch off after a circuit breaker fault times out. The LTC4252-2/LTC4252A-2 provide automatic retry after a fault. The LTC4252A-1/LTC4252A-2 feature tight ±1% undervoltage/overvoltage threshold accuracy. The LTC4252 is available in either an 8-pin or 10-pin MSOP, while the LTC4252A is available in the 10-pin MSOP.

UV/OV %

Latch Off/Retry

Package

LTC4252-1

4.6%

Latch off

MS-8, MS-10

LTC4252-2

4.8%

Retry

MS-8, MS-10

LTC4252A-1

1%

Latch off

MS-10

LTC4252A-2

1%

Retry

MS-10

LTC4252B-1

4.6%

Latch off

MS-8, MS-10

LTC4252B-2

4.6%

Retry

MS-8, MS-10

LTC4252C-1

1%

Latch off

MS-10

LTC4252C-2

1%

Retry

MS-10

Applications

* Hot Board Insertion

* Electronic Circuit Breaker

* –48V Distributed Power Systems

* Negative Power Supply Control

* Central Office Switching

* High Availability Servers

* ATCA

* Allows Safe Board Insertion and Removal from a Live –48V Backplane

* Floating Topology Permits Very High Voltage Operation

* Current Limit With Circuit Breaker Timer

* Fast Response Time Limits Peak Fault Current

* Programmable Soft-Start Current Limit

* Programmable Timer with Drain Voltage Accelerated Response