LT4250L/LT4250H
Negative 48V
Hot Swap Controller
FEATURES
s
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DESCRIPTIO
s
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Allows Safe Board Insertion and Removal
from a Live – 48V Backplane
Circuit Breaker Immunity to Voltage Steps and
Current Spikes
Programmable Inrush and
Short-Circuit Current Limits
Pin Compatible with LT1640L/LT1640H
Operates from –20V to – 80V
Programmable Overvoltage Protection
Programmable Undervoltage Lockout
Power Good Control Output
Bell-Core Compatible ON/OFF Threshold
APPLICATIO S
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The LT
®
4250L/LT4250H are 8-pin, negative 48V Hot Swap
TM
controllers that allow a board to be safely inserted and
removed from a live backplane. Inrush current is limited to
a programmable value by controlling the gate voltage of an
external N-channel pass transistor. The pass transistor is
turned off if the input voltage is less than the program-
mable undervoltage threshold or greater than the over-
voltage threshold. A programmable current limit protects
the system against shorts. After a 500µs timeout the
current limit activates the electronic circuit breaker. The
PWRGD (LT4250L) or PWRGD (LT4250H) signal can be
used to directly enable a power module. The LT4250L is
designed for modules with a low enable input and the
LT4250H for modules with a high enable input.
The LT4250L/LT4250H are available in 8-pin PDIP and SO
packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Hot Swap is a trademark of Linear Technology Corporation.
Central Office Switching
– 48V Distributed Power Systems
Negative Power Supply Control
TYPICAL APPLICATIO
–48V RTN
(SHORT PIN)
–48V RTN
R4
†
549k
1%
3
R5
†
6.49k
1%
R6
†
10k
1%
UV
8
V
DD
1
UV =
38.5V
UV
RELEASE
AT 43V
OV =
71V
LT4250L
2
OV
V
EE
4
SENSE
5
GATE
6
R3
†
1k, 5%
PWRGD
DRAIN
7
V
EE
AND
DRAIN
20V/DIV
*
–48V
INPUT 1
0.1µF
10V
R1
0.02Ω
5%
†
C1
†
470nF
25V
R2
10Ω
5%
C2
†
15nF
100V
2
ON/OFF
9
V
OUT+
8
SENSE
+
7
TRIM
6
SENSE
–
4
5
V
OUT–
V
IN–
1
V
IN+
LUCENT
JW050A1-E
I
D
(Q1)
5A/DIV
Q1
IRF530
–48V
INPUT 2
* DIODES INC. SMAT70A
†
THESE COMPONENTS ARE APPLICATION
SPECIFIC AND MUST BE SELECTED BASED
UPON OPERATING CONDITIONS AND DESIRED
PERFORMANCE. SEE APPLICATIONS
INFORMATION.
C3
0.1µF
100V
5V
+
C4
100µF
100V
+
C5
100µF
16V
4250 TA01
U
Voltage Step On Input Supply
500µs/DIV
4250lhf
U
U
1
LINER [ LINEAR TECHNOLOGY ]
