LTC4251B_15 Datasheet, PDF (1/24 Pages) Linear Technology – Negative Voltage Hot Swap Controllers in SOT-23

LTC4251B/LTC4251B-1/
LTC4251B-2
Negative Voltage
Hot Swap Controllers in SOT-23
FEATURES
n _{Allows Safe Board Insertion and Removal from a}
Live –48V Backplane
n _{Floating Topology Permits Very High Voltage}
Operation
n _{Programmable Analog Current Limit with Circuit}
Breaker Timer
n _{Fast Response Time Limits Peak Fault Current}
n _{Improved Ruggedness Shunt Regulator}
n _{Programmable Timer}
n _{Programmable Undervoltage/Overvoltage Protection}
n _{Low Profile 6-Lead SOT-23 (ThinSOT™) Package}
APPLICATIONS
n _{Hot Board Insertion}
n _{Electronic Circuit Breaker}
n _{–48V Distributed Power Systems}
n _{Negative Power Supply Control}
n _{Central Office Switching}
n _{Programmable Current Limiting Circuit}
n _{High Availability Servers}
n _{Disk Arrays}
DESCRIPTION
The LTC^®4251B/LTC4251B-1/LTC4251B-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 breaker’s response time.
The LTC4251B UV/OV thresholds are designed to match
the standard telecom operating range of – 43V to –75V. The
LTC4251B-1 UV/OV thresholds extend the operating range
to encompass –36V to –72V. The LTC4251B-2 implements
a UV threshold of –43V only. The LTC4251B improves the
ruggedness of the LTC4251 shunt regulator.
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.
TYPICAL APPLICATION
–48V, 2.5A Hot Swap Controller
–48RTN
–48RTN
(SHORT PIN)
R1
402k
1%
R2
32.4k
1%
C1
10nF
R_IN*
10k
500mW
D_IN†
DDZ13B**
V_IN
UV/OV GATE
LTC4251B
TIMER SENSE
V_EE
C_T
150nF
– 48V
*TWO 0.25W RESISTORS IN SERIES FOR
R_IN ON THE PCB ARE RECOMMENDED.
**DIODES, INC.
†RECOMMENDED FOR HARSH ENVIRONMENTS
C_L ⁺
100μF
C_IN
1μF
LOAD
V_OUT
Q1
IRF530S
R_C
10Ω
C_C
18nF
3
1
R_S
0.02Ω
2
4 _{4251b12 TA01a}
GATE
5V/DIV
SENSE
2.5A/DIV
V_OUT
20V/DIV
Start-Up Behavior
1ms/DIV
4251b12 TA01b
4251b12f
1