LTC4260 Linear Technology, LTC4260 Datasheet - Page 13

• Manufacturer Part Number: LTC4260
• Description: Positive High Voltage Hot Swap Controller
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
During a short circuit, if the current limit sense voltage
exceeds 150mV, the active current limit enters a high
current protection mode that immediately turns off the
output transistor by pulling the GATE-to-SOURCE voltage
to zero. Current in the output transistor drops from tens of
amps to zero in a few hundred nanoseconds. The input
voltage will drop during the high current and then spike
upwards due to parasitic inductances when the FET shuts
off (see Supply Transients). Following this event, the part
may turn on again after a delay (typically the 100ms
normal turn-on delay if the input voltage drops below the
UVLO threshold) and enters active current limit before
shutting off.
Overvoltage Fault
An overvoltage fault occurs when the OV pin rises above
its 3.5V threshold. This shuts off the switch immediately
(with a 1mA current from GATE to ground) and sets the
overvoltage present bit, C0, and the overvoltage fault bit
D0. If the OV pin subsequently falls back below the
threshold for 100ms, the switch will be allowed to turn on
again unless the overvoltage autoretry has been disabled
by clearing bit A0.
Undervoltage Fault
An undervoltage fault occurs when the UV pin falls below
its 3.12V threshold. This turns off the switch immediately
(with a 1mA current from GATE to ground) and sets the
undervoltage present bit, C1, and the undervoltage fault bit
D1. If the UV pin subsequently rises above the threshold
for 100ms, the switch will turn on again unless the
50V/DIV
10V/DIV
∆V
5A/DIV
2V/DIV
TIMER
V
GATE
I
OUT
OUT
Figure 3. Short-Circuit Waveforms
U
100µs/DIV
U
W
4260 F03
U
undervoltage autoretry has been disabled by clearing bit
A1. When power is applied to the device, if UV is below its
3.12V threshold after INTV
age lockout threshold, an undervoltage fault will be logged
in the fault register.
Board Present Change of State
Whenever the BD_PRST pin toggles, bit D4 is set to
indicate a change of state. When the BD_PRST pin goes
high, indicating board removal, the switch turns off imme-
diately (with a 1mA current from GATE to ground) and
clears the board present bit, C4. If the BD_PRST pin is
pulled low, indicating a board insertion, all fault bits except
D4 will be cleared and the board present bit, C4, is set. If
the BD_PRST pin remains low for 100ms the state of the
ON pin will be captured in the FET On Control bit A3. This
turns the switch on if the ON pin is tied high. There is an
internal 10µA pull-up current source on the BD_PRST pin.
If the system shuts down due to a fault, it may be desirable
to restart the system simply by removing and reinserting
a load card. In cases where the LTC4260 and the switch
reside on a backplane or midplane and the load resides on
a plug-in card, the BD_PRST pin can be used to detect
when the plug-in card is removed (see Figure 4). Once the
plug-in card is reinserted the fault register is cleared
(except for D4). After 100ms the state of the ON pin is
latched into bit A3 of the control register. At this point the
system will start up again.
If a connection sense on the plug-in card is driving the
BD_PRST pin, the insertion or removal of the card may
cause the pin voltage to bounce. This will result in
clearing the fault register when the card is removed. The
pin can be debounced using a filter capacitor, C
on the BD_PRST pin as shown in Figure 4. The filter time
is given by:
FET Short Fault
A FET short fault will be reported if the data converter
measures a current sense voltage greater than or equal to
2mV while the FET is turned off. This condition sets the FET
short present bit, C5, and the FET short fault bit D5.
t
FILTER
= C
BD_PRST
• 123 [ms/µF]
CC
crosses its 4.5V undervolt-
LTC4260
BD_PRST
13
4260f
,