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AS1367

Datasheet - D e t a i l e d D e s c r i p t i o n

Power-OK

The AS1367’s power-ok is built around an N-channel MOSFET. The circuitry monitors the voltage on pin SET and if the

voltage goes out of regulation (e.g. during dropout, current limit, or thermal shutdown) the pin POK goes low. If the pin

SET is connected to GND an internal resistive-divider is activated and connected to the output. Therefore, the Power-

OK functionality can be realised with no additional external components.

The Power-OK feature is not active during shutdown and provides a power-on-reset function that can operate down to

connect a pull-up resistor from pin POK to pin OUT. Larger values for this resistor will help to minimize current

consumption; a 100k

Ω resistor is perfect for most applications (see Figure 1 on page 1).

Current Limiting

The AS1367 include current limiting circuitry to protect against short-circuit conditions. The circuitry monitors and

controls the gate voltage of the P-channel MOSFET, typically limiting the output current to 180mA. The P-channel

MOSFET output can be shorted to ground for an indefinite period of time without damaging the device.

Thermal-Overload Protection

The devices are protected against thermal runaway conditions by the integrated thermal sensor circuitry. Thermal

shutdown is an effective tool to prevent die overheating since the power transistor is the principle heat source in the

device.

If the junction temperature exceeds 160ºC with 20ºC hysteresis, the thermal sensor starts the shutdown logic, at which

point the P-channel MOSFET is switched off. After the device temperature has dropped by approximately 20ºC, the

thermal sensor will turn the P-channel MOSFET on again. Note that this will be exhibited as a pulsed output under

continuous thermal-overload conditions.

Note: The absolute maximum junction-temperature of +150ºC should not be exceeding during continual operation.

Operating Region and Power Dissipation

Maximum power dissipation is determined by the thermal resistance of the package and circuit board, the temperature

difference between the die junction and the ambient air and the rate of the air flow. The power dissipation of the device

is calculated by:

Maximum power dissipation is calculated by:

Where:

Note: Pin GND is a multi-function pin providing a connection to the system ground and acting as a heat sink. This pin

should be connected to the system ground using a large pad or a ground plane.

(EQ 1)

PI

OUT

V

IN

V

OUT

–

()

×

=

(EQ 2)

P

MAX

T

J

T

AMB

–

θ

JA

-------------------------

=