Positive High Voltage
Hot Swap Controllers
■ Allows Safe Board Insertion and Removal from a
■ Controls Supply Voltage from 10.8V to 80V
■ Foldback Current Limiting
■ Overcurrent Fault Detection
■ Drives an External N-Channel MOSFET
■ Programmable Supply Voltage Power-Up Rate
■ Undervoltage Protection
■ Latch Off Operation Mode (LT4256-1)
■ Automatic Retry (LT4256-2)
■ Available in an 8-Pin SO Package
■ Hot Board Insertion
■ Electronic Circuit Breaker/Power Bussing
■ Industrial High Side Switch/Circuit Breaker
■ 24V/48V Industrial/Alarm Systems
■ Ideally Suited for 12V, 24V and 48V Distributed
■ 48V Telecom Systems
The LT®4256-1/LT4256-2 are high voltage Hot SwapTM
controllers that allow a board to be safely inserted and
removed from a live backplane. An internal driver drives an
external N-channel MOSFET switch to control supply
voltages ranging from 10.8V to 80V.
The LT4256-1/LT4256-2 features an adjustable analog
foldback current limit. If the supply remains in current limit
for more than a programmable time, the N-channel
MOSFET shuts off and the PWRGD output asserts low. The
LT4256-2 automatically restarts after a time-out delay.
The LT4256-1 latches off until the UV pin is cycled low.
The PWRGD output indicates when the output voltage
rises above a programmed level. An external resistor
string from VCC provides programmable undervoltage
The LT4256 can be used as an upgrade to LT1641 designs.
See Table 1 on page 14 for upgraded specifications.
The LT4256-1 and LT4256-2 are available in an 8-pin SO
package that is pin compatible with the LT1641.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Hot Swap is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
48V, 2A Hot Swap Controller
LT4256 Start-Up Behavior
UV = 36V
PWRGD CL = 225µF
PWRGD = 40V