LT4250L/LT4250H
Negative 48V
Hot Swap Controller
FEATURES
DESCRIPTION
Allows Safe Board Insertion and Removal from a
TheLT®4250L/LT4250Hare8-pin,negative48VHotSwap™
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 tran-
sistor is turned off if the input voltage is less than the
programmable undervoltage threshold or greater than
the overvoltage 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.
n
Live –48V Backplane
n
Circuit Breaker Immunity to Voltage Steps and
Current Spikes
n
Programmable Inrush and Short-Circuit Current
Limits
n
Pin Compatible With LT1640L/LT1640H
n
Operates from –18V to –80V
n
Programmable Overvoltage Protection
n
Programmable Undervoltage Lockout
n
Power Good Control Output
n
Bell-Core Compatible ON/OFF Threshold
APPLICATIONS
The LT4250L/LT4250H are available in 8-pin PDIP and
SO packages
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Hot Swap is a
trademark of Linear Technology Corporation.
n
Central Office Switching
n
–48V Distributed Power Systems
n
Negative Power Supply Control
TYPICAL APPLICATION
Voltage Step on Input Supply
–48V RTN
(SHORT PIN)
–48V RTN
R4†
8
549k
1%
V
DD
3
2
V
AND
UV =
EE
DRAIN
20V/DIV
UV
OV
R5†
6.49k
1%
38.5V
1
LT4250L
PWRGD
UV
RELEASE
AT 43V
R6†
10k
1%
OV =
71V
V
SENSE
5
GATE
DRAIN
7
EE
I
D
(Q1)
5A/DIV
4
6
R3†
1k, 5%
*
0.1μF
10V
C1†
470nF
25V
R2
10Ω
5%
4250 TA01b
C2†
15nF
100V
–48V
INPUT 1
500μs/DIV
R1†
0.02Ω
5%
2
Q1
IRF530
ON/OFF
1
9
8
+
–
+
+
–48V
5V
V
V
V
IN
OUT
SENSE
INPUT 2
C3
0.1μF
100V
+
C4
100μF
100V
+
C5
7
6
5
* DIODES INC. SMAT70A
TRIM
100μF
16V
† THESE COMPONENTS ARE APPLICATION
SPECIFIC AND MUST BE SELECTED BASED
UPON OPERATING CONDITIONS AND DESIRED
PERFORMANCE. SEE APPLICATIONS
INFORMATION.
–
SENSE
4
–
V
IN
OUT
4250 TA01a
LUCENT
JW050A1-E
4250lhfa
1