1
425112fd
LTC4251/LTC4251-1/
LTC4251-2
For more information www.linear.com/4251
TYPICAL APPLICATION
FEATURES
DESCRIPTION
Negative Voltage
Hot Swap Controllers in SOT-23
APPLICATIONS
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
Hot Swap and ThinSOT are trademarks of Linear Technology Corporation. All other trademarks
are the property of their respective owners.
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Hot Board Insertion
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Electronic Circuit Breaker
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48V Distributed Power Systems
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Negative Power Supply Control
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Central Office Switching
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Programmable Current Limiting Circuit
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High Availability Servers
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Disk Arrays
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Allows Safe Board Insertion and Removal from a
Live 48V Backplane
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Floating Topology Permits Very High Voltage
Operation
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Programmable Analog Current Limit with Circuit
Breaker Timer
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Fast Response Time Limits Peak Fault Current
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Programmable Timer
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Programmable Undervoltage/Overvoltage Protection
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Low Profile (1mm) ThinSOT" Package
The LTC
?/DIV>
4251/LTC4251-1/LTC4251-2 negative voltage
Hot Swap" controllers allow a board to be safely inserted
and removed from a live backplane. Output current is con-
trolled 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.
Programmable undervoltage and overvoltage detectors
disconnect the load whenever the input supply exceeds
the desired operating range. The supply input is shunt
regulated, allowing safe operation with very high supply
voltages. A multifunction timer delays initial start-up and
controls the circuit breakers response time.
The LTC4251 UV/OV thresholds are designed to match the
standard telecom operating range of 43V to 75V . The
LTC4251-1 UV/OV thresholds extend the operating range
to encompass 36V to 72V . The LTC4251-2 implements
a UV threshold of 43V only.
All parts are available in the 6-Pin SOT-23 package.
48V, 2.5A Hot Swap Controller
Start-Up Behavior
GATE
5V/DIV
SENSE
2.5A/DIV
V
OUT
20V/DIV
425112 TA02
1ms/DIV
+
LTC4251
UV/OV
TIMER
GATE
SENSE
V
IN
V
EE
LOAD
48RTN
48RTN
(SHORT PIN)
D
IN
DDZ13B**
R1
402k
1%
R
C
10
R
S
0.02
R2
32.4k
1%
48V
C
T
150nF
C1
10nF
C
C
18nF
C
IN
1礔
C
L
100礔
R
IN
*
10k
500mW
V
OUT
Q1
IRF530S
425112 TA01
4
3
2
1
*TWO 0.25W RESISTORS IN SERIES FOR
R
IN
ON THE PCB ARE RECOMMENDED.
**DIODES, INC.
RECOMMENDED FOR HARSH ENVIRONMENTS