NCP382
www.onsemi.com
7
FUNCTIONAL DESCRIPTION
Overview
The NCP382 is a dual high side power distribution
switches designed to protect the input supply voltage in case
of heavy capacitive loads, short circuit or over current. In
addition, the high side MOSFETs are turned off during
undervoltage or thermal shutdown condition. Thanks to the
soft start circuitry, NCP382 is able to limit large current and
voltage surges.
Overcurrent Protection
NCP382 switches into a constant current regulation mode
when the output current is above the I
OCP
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 NCP382 will limit the current to the I
OCP
threshold
value until the charge of the capacitor is completed.
VOUTX
IOCP
IOUTX
Drop due to
capacitor charge
Figure 6. Heavy Capacitive Load
− In case of overload, the current is limited to the I
OCP
value and the voltage value is reduced according to the
load by the following relation:
V
OUTX
+ R
LOAD2
I
OCP
(eq. 1)
VOUTX
IOCP
IOUTX
IOCP x RLOAD
Figure 7. Overload
− In case of short circuit or huge load, the current is
limited to the I
OCP
value within T
DET
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 T
SDOCP
value and the
device enters in thermal shutdown (MOSFET is
turned−off).
VOUTX
IOCP
IOUTX
Thermal
Regulation
Threshold
Timer
Regulation
Mode
TREGTOCP
Figure 8. Short−Circuit
Then, the device enters in timer regulation mode, described
in 2 phases:
− Off−phase: Power MOSFET is off during T
OCP
to allow
the die temperature to drop.
− On−phase: regulation current mode during T
REG.
The
current is regulated to the I
OCP
level.
The timer regulation mode allows the device to handle
high thermal dissipation (in case of short circuit for
example) within temperature operating condition.
NCP382 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 overcurrent or overtemperature conditions. When an
overcurrent fault is detected on the power path, FLAG
pin
is asserted low at the end of the associate deglitch time
(TFOCP). 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. The FLAG
pin remains low until the
fault is removed. Then, the FLAG
pin goes high at the end
of T
FGL
Undervoltage Lock−out
Thanks to a built−in under voltage lockout (UVLO)
circuitry, the output remains disconnected from input until
V
IN
voltage is above V
UVLO
. This circuit has a V
HYST
hysteresis witch provides noise immunity to transient
condition.
Thermal Sense
Thermal shutdown turns off the power MOSFET if the die
temperature exceeds T
SD
. A built-in hysteresis prevents the
part from turning on until the die temperature cools at
TRSD.
