US203(2011) データシートの表示（PDF） - Unisonic Technologies
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US203 Datasheet PDF : 7 Pages
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US203
Preliminary
CMOS IC
APPLICATION INFORMATION
Input and Output
VIN (input) is the power source connection to the internal circuitry and the drain of the MOSFET. VOUT (output) is
the source of the MOSFET. In a typical application, current flows through the switch from VIN to VOUT toward the load.
Because the MOSFET is bidirectional when on, if VOUT is greater than VIN, current will flow from VOUT to VIN
There is no a parasitic body diode of N-MOSFET between the drain and source compared to a normal MOSFET,.
The US203 can protect damage from reverse current flow if VOUT being externally forced to a higher voltage than VIN
when the output disabled (VEN > 2V).
Enable Input
The switch will be disabled when the EN pin is in a logic low/high condition. During this condition, the internal
circuitry and MOSFET are turned off, reducing the supply current to 0.1μA typical. Floating the EN may cause
unpredictable operation. EN should not be allowed to go negative with respect to GND. The EN pin may be directly
tied to VIN (GND) to keep the part on.
Soft Start for Hot Plug-In Applications
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.
Fault Flag
The fault flag is an open-drained output of an N-channel MOSFET. The flag drops low to indicate fault conditions:
current limit, thermal shutdown or VOUT < VIN − 1V. In order to reduce energy drain, a large pull-up resistor is required.
100kΩ pull-up resistor is recommended for most applications.
In the case of over current condition, the fault flag is active only if the flag response delay time (tD) has elapsed.
This ensures that FLG is asserted only upon valid over-current conditions and that erroneous error reporting is
eliminated. For example, false over-current conditions may occur during hot-plug events when extremely large
capacitive loads are connected and causes a high transient inrush current that exceeds the current limit threshold.
The FLG response delay time tD is typically 10ms.
Under-Voltage Lockout
UVLO (Under-voltage Lockout) turns off the MOSFET switch once the input voltage falls below 1.3V, and the FLG
is in active. If the input voltage exceeds approximately 1.7V, the switch will be turned on. Under-voltage detection
functions only when the switch is enabled.
Current Limiting and Short-Circuit Protection
The current limit circuit protects the MOSFET switch and the hub downstream port from damage. This circuit
can deliver load current up to the current limit threshold of typically 2.5A through the switch of US203AH/AL and 1A
for US203CH/CL. When an enabled switch applies a heavy load or short circuit, a large-desired transient current
occurs which can cause the current limit circuit response. If this current becomes higher than the current limit
threshold, the devices enter constant current mode until thermal shutdown occurs or the fault is removed.
Thermal Shutdown
The thermal shutdown circuit is used to prevent damage occurs when the die temperature becomes higher than
approximately 130°C. After 20°C of hysteresis, the switch will automatically restart if it enabled. When these devices
are disabled or the fault is removed, the output and FLG signal will continue to cycle on and off.
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