LTC4280
15
4280f
APPLICATIONS INFORMATION
it to INTV
CC
, the part is allowed to turn on again after an
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
DD
pin rises above its
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
CC
crosses its 2.64V undervoltage lockout threshold,
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.
Figure 3. Short-Circuit Waveforms
V
GATE
10V/DIV
V
SOURCE
10V/DIV
V
DD
10V/DIV
I
LOAD
10A/DIV
5µs/DIV
4280 F03
R
S
= 5mΩ
C
L
= 0
R
SHORT
= 1Ω
R6 = 30k
C1 = 0.1µF
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
T
. If the TIMER pin is bypassed by tying
