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ACT6305
(Rev.:2006)

Low Input High Efficiency Synchronous Step-Up DC-DC Converter

Active-Semi, Inc 

ACT6305

Figure 2. Functional Block Diagram

FUNCTIONAL DESCRIPTION

The ACT6305 comprises a reference,

feedback select error comparator, control logic

and timers, internal power MOSFETs and current

comparators. The Functional Block Diagram is

shown in Figure 2.

MAIN CONTROL LOOP

The ACT6305 control architecture utilizes a

series of one-shot and current sense circuits to

regulate the output voltage with very low

quiescent supply current of just 17µA. An ON

cycle begins when FB falls below the ACT6305's

internal reference voltage. 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 until either the 5µs maximum ON

time is exceeded or the 1A current limit is

reached. When either or these conditions occur,

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 START UP

The ACT6305 uses proprietary start-up

circuitry that allows it to achieve very low voltage

startup down to 0.95V. The ACT6305 remains in

low-voltage startup mode until VOUT exceeds

1.85V. The ACT6305 cannot support it's full rated

load current when operating 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 disabled, 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.

Active-Semi, Inc.

-4-

www.active-semi.com

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