US2175

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

7 of 10

www.unisonic.com.tw

QW-R502-403.B

APPLICATION INFORMATION

Fault Flag

The fault flag mainly protects the system from damage caused by such status as thermal shutdown, overcurrent.

Current Limit

The current limit function prevents both excessive in-rush current caused by the plug-in events and the

short-circuit status for MOSFET switches. The current limit threshold is fixed internally, allowing a 1A minimum

current to flow through the MOSFET switches.

Thermal Shutdown

Both thermal shutdown circuits turn both MOSFET switches off if the temperature rises approximately 135°C, at

the same time FLG pin becomes active. 10°C of hysteresis ensures the MOSFETs will not turn on again until the chip

temperature is reduced to 125°C.

Under overcurrent fault conditions, the thermal shutdown will turn off the MOSFET switch which is in this status

due to temperature rise, the other keeps its state.

Supply Filtering

In order to control supply transients, a bypass capacitor placed between IN pin and GND pin is suggested. 0.1μF

to 1μF is suitable. Without a bypass capacitor, an output short may cause sufficient ringing on the input (from supply

lead inductance) to damage internal control circuitry.

Transient Requirements

Ferrite beads are recommended in series with all power and ground connector pins to prevent EMI and

excessive in-rush current generated from input capacitance of down stream during a hot plug-in event. The USB

devices support dynamic attachment (hot plug-in) of peripherals.

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Short Circuit Transient

A 33μF/16V tantalum or a 100μF/10V electrolytic capacitor located closely to downstream connector for each

port is recommended to provide transient protection and a bulk capacitance provides the short-term transient current

needed during a hot-attachment event.

Printed Circuit Layout

To meet the requirements for power circuitry of USB printed circuit boards, maximum thermal consumption and

minimum voltage drop and EMI is required.