AS1383 datasheet(8/22 Pages) AMSCO

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[v1-01] 2015-May-22

AS1383 − Detailed Descriptions

Low-Noise Fixed-Frequency Operation

Oscillator

The AS1383 switching frequency is internally fixed at 3.5MHz

allowing the use of very small external components.

Current Sensing

A signal representing the internal NMOS-switch current is

summed with the slope compensator. The summed signal is

compared to the error amplifier output to provide a peak

current control command for the PWM. Peak switch current is

limited to approximately 650mA independent of VIN or VOUT.

Zero Current Comparator

The zero current comparator monitors the inductor current to

the output and shuts off the PMOS synchronous rectifier once

this current drops to 20mA (approx.). This prevents the inductor

current from reversing polarity and results in improved

converter efficiency at light loads.

Anti-Ringing Control

Anti-ringing control circuitry prevents high-frequency ringing

on pin SW as the inductor current approaches zero. This is

accomplished by damping the resonant circuit formed by the

inductor and the capacitance on pin SW (CSW).

Powersave Operation

In light load conditions, the integrated powersave feature

removes power from all circuitry not required to monitor VOUT.

When VOUT has dropped approximately 1% from nominal, the

device powers up and begins normal PWM operation.

C2 recharges, causing the AS1383 to re-enter powersave mode

as long as the output load remains below the powersave

threshold. The frequency of this intermittent PWM is

proportional to load current; i.e., as the load current drops

further below the powersave threshold, the AS1383 turns on

less frequently. When the load current increases above the

powersave threshold, the AS1383 will resume continuous,

seamless PWM operation.

Shutdown

When pin EN is low the AS1383 is switched off and <1μA current

is drawn from the battery; when pin EN is high the device is

switched on. If EN is driven from a logic-level output, the logic

high-level (on) should be referenced to VOUT to avoid

intermittently switching the device on. In shutdown the battery

input is disconnected from the output.

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