US202

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

5 of 6

www.unisonic.com.tw

QW-R502-445.c

APPLICATION INFORMATION

Input and Output

the power source.

Thermal Shutdown

Thermal shutdown is used to turn off the output MOSFET when the if the temperature is higher than130°C, 20°C

of hysteresis prevents the switch turn on until the die temperature drops to 110°C.

Soft Start

When hot-plug events occur, the soft start is used to eliminate the upstream voltage droop due to the inrush

current. The soft-start protects power supplies from damage caused by highly capacitive loads.

Under-Voltage Lockout

UVLO (Under voltage Lockout) turn off the MOSFET switch once the input voltage falls below 1.8V (TYP.) and if

the input voltage exceeds 1.8V, the switch will be turned on.

Current Limiting and Short Protection

The current limit threshold is preset internally. The minimum value is 1.1A. The current limit circuit protects this

device from damage resulting from undesired excess inrush current, which is encountered during hot plug-in events.

The output current is limited to approximately 1.5A (TYP). When the output is short to ground, it will limit to a

constant current 1A until thermal shutdown or short condition removed.

GND

CE

On

Off

Figure 1. High Side Power Switch with Chip Enable Control

1µF

1µF

Filtering

During the hot-plug events, in order to limit the input voltage drop, a 1μF ceramic capacitor is recommended to

capacitor values will further reduce the voltage drop at the input.

is also necessary for meeting the USB specification during hot plug-in operation.

recommended and higher capacitor values are also preferred.

Choosing these capacitors properly is critical. A lower ESR on the capacitor can get a lower IR drop during the

operation, so the Effective Series Resistance (ESR) of the capacitors must be considered.

For ferrite beads, if they are in series with all power and ground lines, the EMI will be eliminated or reduced. The

DC resistance of the wire kept to a minimum to reduce the voltage drop should be considered in choosing ferrite

beads.

Reverse Current Preventing