US2076

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

5 of 8

www.unisonic.com.tw

QW-R502-446.b

FUNCTIONAL DESCRIPTION

The UTC US2076 is dual high-side switch with active-low enable inputs. Fault conditions turn off or inhibit

turn-on one or both of the output transistors, controlling by the type of fault, and the FLG pin is pulled to ground by

being activated the open-drain error flag transistors.

Input and Output

IN (input) is the power supply connection to the logic circuitry and the source of the output MOSFET.

OUT(output) is the drain of the output A or B MOSFET.

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 driver circuit are also designed to allow the MOSFET drain to be externally forced to

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 and signals the fault flag pin 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 and a fault flag is pulled low. The reaction to an

overcurrent is measured with the following scenarios:

Switch Enable into Heavy Load

If a switch is powered-on or enabled into a heavy load or short-circuit, the switch immediately goes into a

constant-current mode, reducing output voltage. The fault flag goes low until the load is reduced or thermal

shutdown occurs.

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. The fault flag drops low until thermal shutdown occurs or the load is

reduced.

Heavy Load Applied Suddenly 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. In that case, the fault flag

falls until the load is reduced.

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. Both flag pins may be "wire-NORed" to a common pull-up resistor.