AS1353_04 datasheet(10/14 Pages) AMSCO

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AS1353/AS1356

Data Sheet - Deta iled Description

The power-OK feature is not active during shutdown and provides a power-on-reset (POR) function that can operate

down to VIN = 1V. A capacitor to GND may be added to generate a POR delay.

To obtain a logic-level output, connect a pull-up resistor from pin POK to pin OUT. Larger values for this resistor will

help minimize current consumption; a 100k

Ω resistor is perfect for most applications (see Figure 13).

Reverse-Battery Protection

The AS1353/AS1356 contain integrated reverse-battery protection circuitry which monitors the polarity of pins IN and

SHDNM and disconnects the internal circuitry and parasitic diodes if the battery is connected incorrectly. Reverse sup-

ply current is limited to 1mA if VIN = VSHDNM falls below ground. Load current is also limited when VIN or VSHDNM are

reverse biased with respect to ground.

Current Limiting

The AS1353/AS1356 include current limiting circuitry to protect against short-circuit conditions. The circuitry monitors

and controls the gate voltage of the P-channel MOSFET, limiting the output current to 380mA (typ). The P-channel

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

Noise Reduction

The AS1353 uses an external 0.01µF bypass capacitor (CBP) at pin BP to reduce output noise. An internal pre-charge

circuit is used to reduce start-up time.

The use of CBP > 0.01µF improves noise performances but increases start-up time.

Thermal-Overload Protection

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

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

device.

If the junction temperature exceeds 165ºC (typ, AS1356) or 150ºC (typ, AS1353), the thermal sensor starts the shut-

down 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 rating of +150ºC should not be exceeding during continual oper-

ation.

Operating Region and Power Dissipation

Maximum power dissipation is determined by the thermal resistance of the case and circuit board, the temperature dif-

ference between the die junction and ambient air, and the rate of air flow. The power dissipation of the device is calcu-

lated by:

P = IOUT (VIN - VOUT)(EQ 1)

Maximum power dissipation is calculated by:

PMAX = (TJ - TAMB) / (

ΘJB + ΘJA)(EQ 2)

Where:

TJ - TAMB is the temperature difference between the device die junction and the surrounding air.

ΘJB or ΘJC is the thermal resistance of the package.

ΘJA is the thermal resistance through the printed circuit board, copper traces, and other materials to the surrounding

air.

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 ground plane.

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