L1913L-XX-AF5-R datasheet(7/9 Pages) UTC

7 / 9 page

L1913

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

7 of 9

www.unisonic.com.tw

QW-R502-439.b

APPLICATION INFORMATION (Cont.)

Over Current Protection

To monitor the output current, the UTC L1913 applies a current mirror. A portion of the PMOS output transistor’s

current is mirrored to a resistor such that the voltage across this resistor is proportional to the output current. Once

the output current exceeds limit threshold, UTC L1913 would be protected with a limited output current. Further more,

when the output is short to ground, the output current would be folded-back to a less limit.

Note: the input bypass capacitor of 1µF must be placed in the circuit in order to filter out the input voltage spike

caused by the surge current due to the inductive effect of the package pin and the printed circuit board’s routing wire.

Otherwise, the actual voltage at the IN pin may exceed the absolute maximum rating.

Over Temperature Protection

Over-temperature protection circuit is designed to prevent this device from being damaged due to abnormal

temperature during operation. It is used to turn off the output MOSFET if the temperature is higher than 150°C, the

switch does not turn on until the temperature drops to 135°C.

Shutdown Mode

The UTC L1913 enters shutdown mode if the SHDN pin is applied to a logic low voltage. Under the shutdown

state, all the analog circuits are turned off completely, which reduces the current consumption to only the leakage

current. The UTC L1913 output pass transistor would get into high impedance level. There is an internal discharge

path to help to shorten discharge delay time..

Operating Region and Power Dissipation

The UTC L1913 is a linear regulator, so the power dissipation can be expressed by: P = IOUT (VIN – VOUT). And the

maximum power dissipation is calculated by:

PD(MAX) = (TJ–TA)/θJA,=(150°C -25°C)/240°C/W= 520mW

(Where (TJ–TA) is the temperature difference the die and the ambient air; θJA, is the thermal resistance of the

chosen package to the ambient air.)

For surface mount device, heat sinking is accomplished by using the heat spreading capabilities of the PC board

and its copper traces. The die attachment area of the UTC L1913’s lead frame is connected to pin 2, which is the

GND pin. Therefore, the GND pin of UTC L1913 can carry away the heat of the UTC L1913 die very effectively.

Connecting the GND pin to ground using a large ground plane near the GND pin can improve the power

consumption.

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