AS1310 datasheet(12/30 Pages) AMSCO

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[v1-11] 2015-Jan-28

AS1310 − Detailed Description

Hysteretic Boost Converter

Hysteretic boost converters are so called because comparators

are the active elements used to determine ON-OFF timing via

current and voltage measurements. There is no continuously

operating fixed oscillator, providing an independent timing

reference. As a result, a hysteretic or comparator based

converter has a very low quiescent current. In addition, because

there is no fixed timing reference, the operating frequency is

determined by external component (inductor and capacitors)

and also the loading on the output.

Ripple at the output is an essential operating component. A

power cycle is initiated when the output regulated voltage

drops below the nominal value of VOUT (0.99 x VOUT).

Inductor current is monitored by the control loop, ensuring that

operation is always dis-continuous.

The application circuit shown in Figure 2 will support many

requirements. However, further optimization may be useful,

and the following is offered as a guide to changing the passive

components to more closely match the end requirement.

Input Loop Timing

The input loop consists of the source DC supply, the input

capacitor, the main inductor, and the N-channel power switch.

The ON timing of the N-channel switch is determined by a peak

current measurement or a maximum ON time. In the AS1310,

peak current is 400mA (typ) and maximum ON time is 4.2μs

(typ). Peak current measurement ensures that the ON time

varies as the input voltage varies. This imparts line regulation

to the converter.

The fixed ON-time measurement is something of a safety

feature to ensure that the power switch is never permanently

ON. The fixed on-time is independent of input voltage changes.

As a result, no line regulation exists.

Detailed Description

AS1310 데이터시트(PDF) 12 Page - ams AG