NCP380, NCV380
http://onsemi.com
16
FUNCTIONAL DESCRIPTION
Overview
The NCP380 is a high side P channel MOSFET power
distribution switch designed to protect the input supply
voltage in case of heavy capacitive loads, short circuit or
over current. In addition, the high side MOSFET is turned
off during under voltage, thermal shutdown or reverse
voltage condition. Adjustable version allows the user to
program the current limit threshold using an external
resistor. Thanks to the soft start circuitry, NCP380 is able to
limit large current and voltage surges.
Overcurrent Protection
NCP380 switches into a constant current regulation mode
when the output current is above the IOCP threshold.
Depending on the load, the output voltage is decreased
accordingly.
−In case of hot plug with heavy capacitive load, the
output voltage is brought down to the capacitor voltage.
The NCP380 will limit the current to the IOCP threshold
value until the charge of the capacitor is completed.
VOUT
IOCP
IOUT
Drop due to
capacitor charge
Figure 22. Heavy capacitive load
−In case of overload, the current is limited to the IOCP
value and the voltage value is reduced according to the
load by the following relation:
VOUT +RLOAD IOCP (eq. 1)
VOUT
IOCP
IOUT
IOCP x RLOAD
Figure 23. Overload
−In case of short circuit or huge load, the current is
limited to the IOCP value within TDET time until the
short condition is removed. If the output remains
shorted or tied to a very low voltage, the junction
temperature of the chip exceeds TSDOCP value and the
device enters in thermal shutdown (MOSFET is
turned−off).
VOUT
IOCP
IOUT
Thermal
Regulation
Threshold
Timer
Regulation
Mode
TREGTOCP
Figure 24. Short circuit
Then, the device enters in timer regulation mode, described
in 2 phases:
−Off−phase: Power MOSFET is off during TOCP to allow
the die temperature to drop.
−On−phase: regulation current mode during TREG. The
current is regulated to the IOCP level.
The timer regulation mode allows the device to handle
high thermal dissipation (in case of short circuit for
example) within temperature operating condition.
NCP380 stays in on−phase/off−phase loop until the over
current condition is removed or enable pin is toggled.
Remark: Other regulation modes can be available for
different applications. Please contact our On Semiconductor
representative for availability.
FLAG Indicator
The FLAG pin is an open−drain MOSFET asserted low
during over current, reverse−voltage or over temperature
conditions. When an over current or a reverse voltage fault
is detected on the power path, FLAG pin is asserted low at
the end of the associate deglitch time (see electrical
characteristics). Thanks to this feature, the FLAG pin is not
tied low during the charge of a heavy capacitive load or a
voltage transient on output. Deglitch time is TFOCP for over
current fault and TREV for reverse voltage. The FLAG pin
remains low until the fault is removed. Then, the FLAG pin
goes high at the end of TFGL.
Undervoltage Lock−out
Thanks to a built−in under voltage lockout (UVLO)
circuitry, the output remains disconnected from input until
VIN voltage is below VUVLO. When VIN voltage is above
VUVLO, the system try to reconnect the output after a
rearming time. TRUVLO. This circuit has a VHYST hysteresis
witch provides noise immunity to transient.
Thermal Sense
Thermal shutdown turns off the power MOSFET if the die
temperature exceeds TSD. A Hysteresis prevents the part
from turning on until the die temperature cools at TRSD.