LTC4280IUFD#TR Linear Technology, LTC4280IUFD#TR Datasheet - Page 15

• Manufacturer Part Number: LTC4280IUFD#TR
• Manufacturer: Linear Technology

Specifications of LTC4280IUFD#TR

• Lead Free Status / Rohs Status: Supplier Unconfirmed

APPLICATIONS INFORMATION
Overcurrent Fault
The LTC4280 features an adjustable current limit that
protects against short-circuits or excessive load current
until an overcurrent fault is generated. An overcurrent
fault can occur in two different manners. First, at the end of
start-up when the TIMER pin reaches its 1.235V threshold
or the internal 100ms start-up timer expires, if the part is
in current limit an overcurrent fault is generated. Second,
after start-up the FILTER pin ramps up with 10μA if the sense
voltage exceeds the 25mV circuit breaker threshold or the
current limit circuit regulates the sense voltage. When the
FILTER pin passes its 1.235V threshold the overcurrent
present bit C2 is set and an overcurrent fault is generated.
In both cases the external MOSFET is turned off and the
overcurrent fault bit is set.
After the MOSFET is turned off, the TIMER and FILTER
capacitors begins discharging with 2μA pulldown currents.
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
V
10V/DIV
10V/DIV
10V/DIV
10A/DIV
SOURCE
V
I
LOAD
GATE
V
DD
R
C
R
R6 = 30k
C1 = 0.1μF
Figure 3. Short-Circuit Waveforms
L
S
SHORT
= 0
= 5mΩ
T
= 1Ω
. If the TIMER pin is bypassed by tying
5μs/DIV
4280 F03
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
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 applied
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.
CC
crosses its 2.64V undervoltage lockout threshold,
CC
, the part is allowed to turn on again after an
DD
pin rises above its
LTC4280
15
4280f