LTC4251B/LTC4251B-1/
LTC4251B-2
Negative Voltage
Hot Swap Controllers in SOT-23
FEATURES
DESCRIPTION
TheLTC®4251B/LTC4251B-1/LTC4251B-2negativevoltage
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, activecurrentlimitingandafastfeedforwardpath
that limits peak current under worst-case catastrophic
fault conditions.
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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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Improved Ruggedness Shunt Regulator
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 breaker’s response time.
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Programmable Timer
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Programmable Undervoltage/Overvoltage Protection
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Low Profile 6-Lead SOT-23 (ThinSOT™) Package
APPLICATIONS
The LTC4251B UV/OV thresholds are designed to match
thestandardtelecomoperatingrangeof–43Vto–75V.The
LTC4251B-1UV/OVthresholdsextendtheoperatingrange
toencompass–36Vto–72V. TheLTC4251B-2implements
a UV threshold of –43V only. The LTC4251B improves the
ruggedness of the LTC4251 shunt regulator.
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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
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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High Availability Servers
Disk Arrays
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TYPICAL APPLICATION
–48V, 2.5A Hot Swap Controller
Start-Up Behavior
–48RTN
R
*
IN
+
–48RTN
(SHORT PIN)
10k
GATE
5V/DIV
C
L
LOAD
500mW
100μF
R1
402k
1%
V
OUT
†
C
D
IN
IN
V
IN
1μF
DDZ13B**
Q1
IRF530S
SENSE
2.5A/DIV
UV/OV GATE
LTC4251B
C1
10nF
3
4
TIMER SENSE
1
R2
32.4k
1%
R
10Ω
C
R
V
V
S
EE
OUT
0.02Ω
20V/DIV
C
C
C
T
2
18nF
150nF
4251b12 TA01a
–48V
4251b12 TA01b
1ms/DIV
*TWO 0.25W RESISTORS IN SERIES FOR
R
ON THE PCB ARE RECOMMENDED.
IN
**DIODES, INC.
†RECOMMENDED FOR HARSH ENVIRONMENTS
4251b12f
1