LTC4253ACGN#PBF Linear Technology, LTC4253ACGN#PBF Datasheet - Page 14

• Manufacturer Part Number: LTC4253ACGN#PBF
• Description: IC HOT SWAP CONTRLR -48V 16-SSOP
• Manufacturer: Linear Technology
• Type: Hot-Swap Controllerr

Specifications of LTC4253ACGN#PBF

• Applications: General Purpose
• Internal Switch(s): No
• Voltage - Supply: 8.2 V ~ 14.5 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP (0.150", 3.90mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

operaTion
LTC4253/LTC4253A
Higher overloads are handled by an analog current limit
loop. If the drop across R
limiting loop servos the MOSFET gate and maintains a
constant output current of V
V
and this increases MOSFET heating. If V
connecting an external resistor, R
DRAIN allows the fault timing cycle to be shortened by
accelerating the charging of the TIMER capacitor. The
TIMER pull-up current is increased by 8 • I
because SENSE > 50mV, TIMER charges C
time, and the LTC4253/LTC4253A eventually shut down.
Low impedance failures on the load side of the LTC4253/
LTC4253A, coupled with 48V or more driving potential,
can produce current slew rates well in excess of 50A/µs.
Under these conditions, overshoot is inevitable. A fast
SENSE comparator with a threshold of 200mV detects
overshoot and pulls GATE low much harder and hence
much faster than the weaker current limit loop. The V
R
rent as previously described. As before, TIMER runs and
shuts down the LTC4253/LTC4253A when C
applicaTions inForMaTion
SHUNT REGULATOR
A fast responding shunt regulator clamps the V
13V (V
current limiting resistor, R
C
at start-up.
To meet creepage requirements R
or more series connected units. This introduces a wider
total spacing than is possible with a single component
while at the same time ballasting the potential across the
gap under each resistor. The LTC4253 is fundamentally a
low voltage device that operates with –48V as its reference
ground. To further protect against arc discharge into its
14
OUT
IN
S
current limit loop then takes over and servos the cur-
filters supply transients and contributes a short delay
(MOSFET drain-source voltage drop) typically rises
Z
). Power is derived from –48RTN by an external
IN
ACL
S
. A 1µF decoupling capacitor,
reaches V
/R
S
IN
. In current limit mode,
D
may be split into two
between V
ACL
OUT
DRN
, the current
T
T
reaches 4V.
during this
. Note that
> V
IN
OUT
DRNCL
pin to
ACL
and
,
/
If C
5µA pull-up current source. The LTC4253/LTC4253A circuit
breaker latch is reset by either pulling the RESET pin active
high until TIMER goes low, pulling UV momentarily low,
dropping the input voltage V
threshold or pulsing TIMER momentarily low with a switch.
Although short-circuits are the most obvious fault type,
several operating conditions may invoke overcurrent
protection. Noise spikes from the backplane or load, input
steps caused by the connection of a second, higher voltage
supply, transient currents caused by faults on adjacent
circuit boards sharing the same power bus or the insertion
of non-hot swappable products could cause higher than
anticipated input current and temporary detection of an
overcurrent condition. The action of TIMER and C
these events allowing the LTC4253/LTC4253A to “ride out”
temporary overloads and disturbances that could trip a
simple current comparator and, in some cases, blow a fuse.
pins, the area in and around the LTC4253 and all associ-
ated components should be free of any other planes such
as chassis ground, return, or secondary-side power and
ground planes.
V
accomodate external loading such as the PWRGD opto-
couplers shown in Figure 2. As an alternative to running
higher current, simply buffer V
as shown in Figure 3. A method that cascodes the PWRGD
outputs as shown in Figure 17.
V
the package, and is tested to survive a 100µs, 100mA
IN
IN
T
may be biased with additional current up to 30mA, to
is rated to handle 30mA within the thermal limits of
reaches 4V, the LTC4253/LTC4253A latch off with a
IN
IN
below the internal UVLO
with an emitter follower
T
rejects
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