US1528

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

5 of 8

www.unisonic.com.tw

QW-R502-457.b

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

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.