Datasheet

LTC4253B
12
4253bf
operaTion
Hot Circuit Insertion
When circuit boards are inserted into a live backplane,
the supply bypass capacitors can draw huge transient
currents from the power bus as they charge. The flow
of current damages the connector pins and glitches the
power bus, causing other boards in the system to reset.
The LTC4253B is designed to turn on a circuit board sup-
ply in a controlled manner, allowing insertion or removal
without glitches or connector damage.
Initial Start-Up
The LTC4253B resides on a removable circuit board and
control the path between the connector and load or power
conversion circuitry with an external MOSFET switch (see
Figure 1). Both inrush control and short-circuit protection
are provided by the MOSFET.
A detailed schematic is shown in Figure 2. –48V and
–48RTN receive power through the longest connector pins
and are the first to connect when the board is inserted. The
GATE pin holds the MOSFET off during this time. UV/OV
determines whether or not the MOSFET should be turned
on based upon internal high accuracy thresholds and an
external divider. UV/OV does double duty by also moni-
toring whether or not the connector is seated. The top of
the divider detects –48RTN
by way of a short connector
pin that is the last to mate during the insertion sequence.
Figure 2. –48V/2.5A Application with a Wider Operating Range
Figure 1. Basic LTC4253B Hot Swap Topology
LTC4253B
–48RTN
4253b F01
PLUG-IN BOARD
–48V
BACKPLANE
+
C
LOAD
ISOLATED
DC/DC
CONVERTER
MODULE
LOW
VOLTAGE
CIRCUITRY
+
–
+
–
R5
5.6k
R4
5.6k
R6
5.6k
PWRGD1
V
IN
V
EE
LTC4253B
POWER
MODULE 1
PWRGD2
PWRGD3
EN3
EN2
UV
OV
RESET
DRAINSS
GATESQTIMER
SENSETIMER
EN
POWER
MODULE 2
EN
POWER
MODULE 3
EN
R
IN
2.5k
15k(1/4W)/6
PUSH
RESET
EN3
4253b F02
EN2
R
C
10Ω
R
D
1M
R
S
0.02Ω
Q1
IRF530S
V
IN
C
C
18nF
C
T
0.33µF
C1
10nF
–48RTN
(LONG PIN)
–48RTN
(SHORT PIN)
–48V
(LONG PIN)
C
SQ
0.1µF
C
SS
68nF
R7
POWER
MODULE 1
OUTPUT
POWER
MODULE 2
OUTPUT
V
IN
R8
+
C
L
100µF
C
IN
1µF
D
IN
††
DDZ13B*
R1
38.3k
1%
R3
432k
1%
R9
47k
R2
4.75k
1%
† † †
†
†
*DIODES, INC.
†
MOC207
††
RECOMMENDED FOR HARSH ENVIRONMENTS.
V
IN