US205XG-S08-R datasheet(4/5 Pages) UTC

4 / 5 page

US205

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

4 of 5

www.unisonic.com.tw

QW-R502-609.A

APPLICATION INFORMATION

The UTC US205 is an enable input single N-MOSFET high-side power switches, optimized for self-powered and

bus-powered Universal Serial Bus (USB) applications. A charge pump circuitry is contained to drive the internal

MOSFET switch, the switch on resistance is 100mΩ, meets USB voltage droop requirements.

Input and Output

VIN (Input) is both the power supply connection for the internal circuitry driving the switch and the input (Drain

connection) of the power MOSFET switch. VOUT (Output) is the Source connection of the MOSFET and supplies

power to the load. In a typical circuit, current flows from VIN to VOUT toward the load. Since the switch is bidirectional

when enabled, if VOUT is greater than VIN, current will flow through the switch from VOUT to VIN.

There is no parasitic body diode between drain and source of the MOSFET, prevents reverse current flow if VOUT

is externally forced to a higher voltage than VIN when the chip is disabled (VEN < 0.8V).

Normal MOSFET

UTC US205

Chip Enable Input

If the EN pin is in a logic low condition the UTC US205 switch will be disabled. During this case, MOSFET and the

internal circuitry will be turned off, and the supply current is reduced to 0.1uA typical. When the EN is floating,

unpredictable operation may be caused. EN goes negative with respect to GND should not be allowed. The EN pin

can be directly tied to VIN.

Soft Start for Hot Plug-In Applications

The UTC US205 “soft-start” feature eliminates the upstream voltage droop caused by the large inrush current

during hot-plug events, and effectively isolates the power source from extremely large capacitive load, meets the

USB voltage droop requirements.

Under-Voltage Lockout

The UTC US205 internal Under-voltage lockout (UVLO) circuit prevents the MOSFET switch from turning on until

the input voltage exceeds approximately 1.75V. The internal MOSFET switch will be turned off if input voltage drops

below approximately 1.7V. Under-voltage detection functions only when the chip is enabled.

Current Limiting and Short-Circuit Protection

The UTC US205 protects the power supply and the load from damage by the current limit circuitry, but can deliver

load current up to the current limit threshold (typically 2A). If an enabled switch encounters a heavy load or short

circuit case, a large transient current may flow until the current limit circuitry responds. Once this current limit

threshold level is exceeded, the device enters constant current mode until the fault is removed or thermal shutdown

occurs.

Supply Filter/Bypass Capacitor

To prevent the input voltage drooping during hot-plug events, a 1uF low-ESR ceramic capacitor from VIN to GND is

strongly recommended. But higher capacitor values will further reduce the voltage droop on the input. Furthermore,

without the bypass capacitor, an output short may cause sufficient ringing on the input (from source lead inductance)

to destroy the internal circuitry. The input voltage transient must not exceed the absolute maximum supply voltage

6V even for a short duration.

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