ML3440 datasheet(7/13 Pages) ETC1

7 / 13 page

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Rev. B, Sep 2005

Operation (3)

Low Noise Fixed Frequency Operation

Burst Mode Operation (2)

Figure 4

Inductor Discharge Cycle During Burst Mode Operation

Burst Mode Operation to Fixed Frequency

Transient Response

When transitioning from Burst Mode operation to fixed

frequency, the system exhibits a transient since the modes

of operation have changed. For most systems this transient

is acceptable, but the application may have stringent input

current and/or output voltage requirements that dictate a

broad-band voltage loop to minimize the transient.

Lowering the DC gain of the loop will facilitate the task (10M

FB to Vc) at the expense of DC load regulation.

SOFT-START

The soft-start function is combined with shutdown. When

the SHDN/SS pin is brought above typically 1V, the IC is

enabled but the EA duty cycle is clamped from the Vc pin.

A detailed diagram of this function is shown in Figure 5.

The components Rss and Css provide a slow ramping

voltage on the SHDN/SS pin to provide a soft-start

function.

Figure 5 Soft-Start Circuitry

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