LT4250L/LT4250H
Negative 48V
Hot Swap Controller
U
FEATURES
DESCRIPTIO
TheLT®4250L/LT4250Hare8-pin,negative48VHotSwapTM
controllers that allow a board to be safely inserted and
removedfromalivebackplane. Inrushcurrentislimitedto
aprogrammablevaluebycontrollingthegatevoltageofan
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.
■
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 CompaUtible ON/OFF Threshold
APPLICATIO S
■
The LT4250L/LT4250H are available in 8-pin PDIP and SO
packages.
Central Office Switching
■
–48V Distributed Power Systems
■
, LTC and LT are registered trademarks of Linear Technology Corporation.
Negative Power Supply Control
Hot Swap is a trademark of Linear Technology Corporation.
U
TYPICAL APPLICATIO
–48V RTN
(SHORT PIN)
–48V RTN
R4†
Voltage Step On Input Supply
8
549k
1%
V
DD
3
2
UV =
UV
OV
R5†
6.49k
1%
38.5V
1
LT4250L
PWRGD
UV
RELEASE
AT 43V
R6†
10k
1%
OV =
71V
V
SENSE
5
GATE
6
DRAIN
7
EE
V
AND
EE
DRAIN
20V/DIV
4
R3†
1k, 5%
*
0.1µF
10V
C1†
470nF
25V
R2
10Ω
5%
C2†
15nF
100V
–48V
INPUT 1
R1†
0.02Ω
5%
I
(Q1)
D
5A/DIV
2
Q1
IRF530
ON/OFF
1
9
8
+
–
+
+
–48V
5V
V
V
V
500µs/DIV
IN
OUT
SENSE
INPUT 2
C3
0.1µF
100V
C4
+
C5
+
7
6
5
* DIODES INC. SMAT70A
100µF
TRIM
100µF
16V
† THESE COMPONENTS ARE APPLICATION
SPECIFIC AND MUST BE SELECTED BASED
UPON OPERATING CONDITIONS AND DESIRED
PERFORMANCE. SEE APPLICATIONS
INFORMATION.
100V
–
SENSE
4
–
V
IN
OUT
4250 TA01
LUCENT
JW050A1-E
4250lhf
1