ltc4215-1 Linear Technology Corporation, ltc4215-1 Datasheet - Page 13

• Manufacturer Part Number: ltc4215-1
• Description: Hot Swap Controller With Adc And I2c Compatible Monitoring
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
Overcurrent Fault
The LTC4215-1 features an adjustable current limit that
protects against short circuits or excessive load current.
An overcurrent fault occurs when the circuit breaker 25mV
threshold has been exceeded for longer than the 20μs
time-out delay. Current limiting begins immediately when
the current sense voltage between the V
pins reaches 75mV. The GATE pin is then brought down
and regulated in order to limit the current sense voltage to
75mV. When the 20μs circuit breaker time out has expired,
the external MOSFET is turned off and the overcurrent fault
bit D2 is set.
After the MOSFET is turned off, the TIMER capacitor
begins discharging with a 2μA pull-down current. When
the TIMER pin reaches its 0.2V threshold the MOSFET is
allowed to turn on again if the overcurrent fault has been
cleared. However, if the overcurrent auto-retry bit, A2 has
been set then the MOSFET turns on again automatically
without resetting the overcurrent fault. Use a minimum
value of 10nF for C
it to INTV
internal 5 second timer has expired, in the same manner
as the TIMER pin passing its 0.2V threshold.
Overvoltage Fault
An overvoltage fault occurs when either the OV pin rises
above its 1.235V threshold, or the V
15.6V threshold, for more than 2μs. This shuts off the GATE
with a 1mA current to ground and sets the overvoltage
V
10V/DIV
10V/DIV
10V/DIV
10A/DIV
SOURCE
V
I
LOAD
GATE
V
DD
CC
R
C
R
R6 = 30k
C1 = 0.1μF
S
L
SHORT
, the part is allowed to turn on again after an
= 0
= 5mΩ
Figure 3. Short-Circuit Waveforms
= 1Ω
T
. If the TIMER pin is bypassed by tying
5μs/DIV
DD
pin rises above its
DD
4215 F03
and SENSE
present bit C0 and the overvoltage fault bit D0. If the pin
subsequently falls back below the threshold for 100ms,
the GATE is allowed to turn on again unless overvoltage
auto-retry has been disabled by clearing bit A0.
Undervoltage Fault
An undervoltage fault occurs when the UV pin falls below
its 1.235V threshold for more than 2μs. This turns off the
GATE with a 1mA current to ground and sets undervoltage
present bit C1 and undervoltage fault bit D1. If the UV pin
subsequently rises above the threshold for 100ms, the
GATE is turned on again unless undervoltage auto-retry
has been disabled by clearing bit A1. When power is ap-
plied to the device, if UV is below its 1.235V threshold after
INTV
an undervoltage fault is logged in the fault register.
Board Present Change of State
Whenever the EN pin toggles, bit D4 is set to indicate a
change of state. When the EN pin goes high, indicating
board removal, the GATE turns off immediately (with a 1mA
current to ground) and clears the board present bit, C4. If
the EN pin is pulled low, indicating a board insertion, all
fault bits except D4 are cleared and enable bit, C4, is set.
If the EN pin remains low for 100ms the state of the ON
pin is captured in ‘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 EN 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 LTC4215-1 and the switch
reside on a backplane or midplane and the load resides on
a plug-in card, the EN pin detects when the plug-in card is
removed. Figure 4 shows an example where the EN pin is
used to detect insertion. 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 starts up again.
If a connection sense on the plug-in card is driving the EN
pin, insertion or removal of the card may cause the pin
voltage to bounce. This results in clearing the fault register
when the card is removed. The pin may be debounced
CC
crosses its 2.64V undervoltage lockout threshold,
LTC4215-1
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