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AS1341

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

Dropout Voltage

A buck converter’s minimum input-to-output voltage differential (dropout voltage) determines the lowest usable supply

voltage. In battery-powered systems, this limits the useful end-of-life battery voltage. To maximize battery life, the

AS1341 operates with duty cycles up to 100%, which minimizes the dropout voltage and eliminates switching losses

while in dropout. When the supply voltage approaches the output voltage, the P-channel MOSFET remains on contin-

uously to supply the load.

Note: Dropout voltage is defined as the difference between the input and output voltages when the input is low

enough for the output to drop out of regulation.

For a step-down converter with 100% duty cycle, dropout is related to the MOSFET drain-to-source on-resistance

Shutdown

A logic low on pin SHDNN shuts down the AS1341; a logic high on SHDNN powers on the device.

In shutdown mode the supply current drops to 0.8µA to maximize battery life, and the internal P-channel MOSFET

turns off to isolate the output from the input. The output capacitance and load current determine the output voltage

decay rate.

Note: Pin SHDNN should not be left floating. If the shutdown feature is not used, connect SHDNN to IN.

Power-OK Output

The AS1341 provides a Power OK output (POK) that goes high-impedance when the output reaches 92.5% of its reg-

ulation point. POK goes low when the output is below 92.5% of the regulation point and the AS1341 is turned on

(IN

≥ 4.5V and SHDNN ≥ 2.4V). A 12kΩ to 1MΩ pullup resistor between pin POK and pin IN or pin OUT or another volt-

age (

≤ IN) can provide a microprocessor logic control signal.

Note: Connect pin POK to GND when the Power-Ok feature is not used.

Thermal-Overload Protection

Integrated thermal-overload protection limits total power dissipation in the AS1341. During continuous thermal-over-

pass transistor, allowing the AS1341 to cool down. When the AS1341 junction temperature cools by 10ºC, the thermal

sensor turns the pass transistor on again resulting in a pulsed output.