NCP374 データシートの表示（PDF） - ON Semiconductor

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NCP374

Overvoltage Up to +30 V and Down to -30 V with Load Switch Function

ON Semiconductor 

NCP374

TYPICAL OPERATING CHARACTERISTICS

Operation

The NCP374 acts as an over−voltage in charge mode,

when wall adapter or Vbus cable is connected to Vbus pin

of the device. The downstream system (transceiver, CCCV

charger..) are protected up to +30 V if charging voltage

exceeds OVLO threshold (5.77 V). Due to a back to back

architecture, the Vbus pin is also protected against reverse

polarity connection, coming from wrong USB cables. This

negative protection acts down to −30 V.

In disable mode (EN = 1, DIR = 1), there is no current

consumption on IN pin and MSOFETs are turned off (Vbus

cable disconnected)

The NCP374 provides over−current from IN to Vbus by

selecting Vbus mode.

To active Vbus mode (USB port on), the EN pin must be

tied low. In this case, MOSFET are turned on and current is

measure in the branch. If the sinking current on the Vbus pin

is above the programmed current on Ilim pin (can be

programmed up to TBD), the Vbus current is regulated

around Iocp during treg time. If the overload is present at the

end of this timer, the Mosfet are turned off and automatic

rearming cycle is activated. With Treg/Trrd cycle until

overload is present.

Over−voltage Lockout (OVLO)

To protect the connected system on IN pins, from external

over−voltage coming from USB connector or Wall Adapter,

through Vbus pin , the device has a built−in over−voltage

lock out (OVLO) circuit. During over−voltage condition,

the output remains disabled until the input voltage exceeds

OVLO (Vbus pin).

The OVLO comparator is available in all modes.

Additional OVLO thresholds ranging from OVLO can be

manufactured. Please contact your ON Semiconductor

representative for further information.

FLAG output is tied to low until Vin is higher than OVLO.

This circuit has a built−in hysteresis to provide noise

immunity to transient conditions.

Over−Current Protection (OCP)

This device integrates over current protection function,

from IN to Vbus port.

That means the current across the internal NMOS is

regulated when the value, set by external Rlim resistor,

exceeds Ilimit during an internal timer.

An internal resistor is placed in series with the pin

allowing to have a maximum OCP value when I lim pin is

directly connected to GND.

By adding external resistors in series with I lim and GND,

the OCP value is decreased. The Rlim tolerance is important

to keep a good accuracy. So a value between 0.1% and 1%

won’t have an impact on the OCP accuracy. Nevertheless,

the higher Rlim value, the lower Over current protection

accuracy.

Indeed, the current is measured by a voltage comparator

on a serial resistance. If this voltage drop comes very small,

the offset of the internal comparator will have an impact on

the accuracy. So a division by more than three times with

Rlim will degrade drastically the overcurrent accuracy.

The current limit calculation formula for the

NCP374MU075TXG is:

Rlim(W) + 22150ńIocp * 29035

During over current event, NMOSes are opened and

FLAG output is tied to low, allowing the mController to take

into account the fault event and then disable reverse charge

path.

VBus Mode

To access to the Vbus mode, DIR pin must be tied to high

(>1.2) and EN must be tied from high to low (< 0.4 V).

In that case, the core of the NCP374 will be supplied by

the IN, with a 2.5 V minimum voltage and 5.5V maximum

voltage.

In this state, OCP, OVLO and thermal modes are

available.

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