US1528_15 Datasheet, PDF (5/8 Pages) Unisonic Technologies – USB HIGH-SIDE POWER SWITCH ADVANCE INFORMATION

US1528
Preliminary
CMOS IC
„ FUNCTIONAL DESCRIPTION
The UTC US1528 is high-side single channel power switch; it has an enable input in active low. Fault
conditions turn off or inhibit turn-on of the output transistors.
Input and Output
IN pin (input) is the power supply connection to the logic circuitry and the source of the output MOSFET. OUT
pin (output) is the output MOSFET’s drain. Current flows through the switch from IN pin to OUT pin toward the load
in many applications. All OUT pins must be connected together to the load.
The output MOSFET and driving circuit are also designed to allow the MOSFET drain to be externally forced to
a higher voltage than the source (V_OUT > V_IN) when the switch is off. This avoids undesirable drain-to-body diode
current flow by connecting the body to the most positive voltage. If V_OUT >V_IN when switch is enabled, current will
flow from V_OUT to V_IN.
Thermal Shutdown
Thermal shutdown is designed to prevent this device from being damaged due to excessive power dissipation.
It is used to turn off the output MOSFET if the temperature is higher than135°C, 10°C of hysteresis prevents the
switch from turning on until the die temperature drops to 125°C. Thermal shutdown circuit functions only when the
switch is enabled.
Undervoltage Lockout
UVLO (Undervoltage Lockout) turns off the MOSFET switch once the input voltage falls below 2.3V (TYP) and
if the input voltage exceeds 2.5V (TYP), the switch will be turned on. UVLO detection functions only when the switch
is enabled.
Current Sensing and Limiting
The current limit threshold is fixed internally, allowing a 0.5A minimum current to flow through the output
MOSFET. However, the current limit threshold can prevent the output MOSFET and external load from being
damage. A current sense circuit protects the MOSFET switch’s output current. If output current becomes higher than
the current limit threshold, the output MOSFET switch is turned off. The reaction to an overcurrent is measured with
the following scenarios:
Switch Enabled into Heavy Load
If the switch is powered on or enabled into a heavy load or short-circuit, the switch enters a constant-current
mode immediately, reducing the output voltage.
Heavy Load Applied to Enabled Switch
When a heavy load is applied, a large-undesired transient current occurs which may damage the switch. Then
the current limit circuit may turn off the switch, folding back into constant-current mode.
Fault Flag
Fault flag is an open-drained output of an N-channel MOSFET. It drops low to indicate error conditions as
follows: current limiting, UVLO, or thermal shutdown. The flag output MOSFET is capable of sinking a 10mA load to
typically 100mV above ground.
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
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