AS1324 datasheet(9/20 Pages) AMSCO

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AS1324

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

Powersave Operation

The AS1324 uses an automatic powersave mode where the peak inductor current (IPK) is set to approximately 200mA

while independent of the output load. In powersave mode, load current is supplied solely from the output capacitor. As

the output voltage drops, the error amplifier output rises above the powersave threshold signaling to switch into PWM

fixed frequency mode and turn the PMOS on. This process repeats at a rate determined by the load demand.

Each burst event can last from a few cycles at light loads to almost continuous cycling (with short sleep intervals) at

moderate loads. In between bursts, the power MOSFETs are turned off, as is any unneeded circuitry, reducing quies-

cent current to 30µA.

Short-Circuit Protection

In cases where the AS1324 output is shorted to ground, the oscillator frequency (fOSC) is reduced to 1/13 the nominal

frequency (

≅ 115kHz). This frequency reduction ensures that the inductor current has more time to decay, thus pre-

venting runaway conditions. fOSC will progressively increase to 1.5MHz when VFB/VOUT > 0V.

Shutdown

Connecting EN to GND or logic low places the AS1324 in shutdown mode and reduces the supply current to 0.1µA. In

shutdown the control circuitry and the internal NMOS and PMOS turn off and SW becomes high impedance discon-

necting the input from the output. The output capacitance and load current determine the voltage decay rate. For nor-

mal operation connect EN to VIN or logic high.

Note:

Pin EN should not be left floating.

AS1324 Datasheet(PDF) 9 Page - ams AG