ACT6305

Rev 2, 22-Feb-11

Innovative Power

TM

- 7 -

www.active-semi.com

Copyright © 2011 Active-Semi, Inc.

FUNCTIONAL DESCRIPTION

As seen in the Functional Block Diagram, the

ACT6305 comprises a reference, low input startup

circuitry, feedback select, error comparator, control

logic and timers, internal power MOSFETs and cur-

rent comparators.

Main Control Loop

The ACT6305 control architecture utilizes a series

of one-shot and current sense circuits to regulate

the output voltage with a very low quiescent supply

current of just 17µA. An ON cycle begins when FB

falls below the ACT6305’s internal reference volt-

age. During an ON cycle, the N-channel power

switch is turned on to connect the LX node to

ground, transferring energy from input supply to the

inductor. The ON cycle persists or the 1A current

limit is reached. When either of these conditions

occurs, the N-channel power switch turns off and

the OFF cycle begins. During the OFF cycle, the

energy stored in the inductor is released into the

output capacitor and load through the synchronous

rectifier. Once the 1µs minimum OFF time expires,

another ON cycle begins when the FB voltage

drops below the reference voltage.

Light Load Operation

Under light load conditions, the IC automatically

enters a power-saving mode by extending the OFF

time. This reduces switching losses and allows the

ACT6305 to maintain high efficiency across a very

wide load range.

Low Voltage Startup

The ACT6305 uses proprietary start-up circuitry that

allows it to achieve very low voltage startup down to

1V. The ACT6305 remains in low voltage startup

not support its full rated load current when operat-

ing in low-voltage startup mode. Care should be

taken to minimize load current during startup.

Shutdown

In shutdown mode, all internal circuits including the

power switch and the synchronous rectifier are dis-

abled, reducing quiescent supply current to less

than 1µA. Note that in shutdown mode, a DC path

from the input supply to the output still exists due to

the body diode of the synchronous rectifier.

FUNCTIONAL BLOCK DIAGRAM

OUT

LX

G

REFERENCE

FEEDBACK

SELECT

DRIVER

ERROR

COMPARATOR

LOW INPUT

START UP

1µs

ONE -SHOT

5µs

ONE -SHOT

SET

LATCH Q

RESET

CURRENT LIMIT

COMPARATOR

EN

FB