Innovative Power

TM

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www.active-semi.com

Copyright © 2012 Active-Semi, Inc.

ACT4065A

Rev 0, 23-Apr-12

®

FUNCTIONAL BLOCK DIAGRAM

FUNCTIONAL DESCRIPTION

As seen in, Functional Block Diagram, the AC-

T4065A is a current mode pulse width modulation

(PWM) converter. The converter operates as fol-

lows:

A switching cycle starts when the rising edge of the

Oscillator clock output causes the High-Side Power

Switch to turn on and the Low-Side Power Switch to

turn off. With the SW side of the inductor now con-

nected to IN, the inductor current ramps up to store

energy in its magnetic field. The inductor current

level is measured by the Current Sense Amplifier

and added to the Oscillator ramp signal. If the re-

sulting summation is higher than the COMP volt-

age, the output of the PWM Comparator goes high.

When this happens or when Oscillator clock output

goes low, the High-Side Power Switch turns off and

the Low-Side Power Switch turns on. At this point,

the SW side of the inductor swings to a diode volt-

age below ground, causing the inductor current to

decrease and magnetic energy to be transferred to

the output. This state continues until the cycle starts

again.

The High-Side Power Switch is driven by logic us-

ing the BS bootstrap pin as the positive rail. This pin

Switch turns on.

The COMP voltage is the integration of the error

between the FB input and the internal 0.808V refer-

ence. If FB is lower than the reference voltage,

COMP tends to go higher to increase current to the

output. Current limit happens when COMP reaches

its maximum clamp value of 2.0V.

The Oscillator normally switches at 210kHz. How-

ever, if the FB voltage is less than 0.6V, then the

switching frequency decreases until it reaches a

Shutdown Control

The ACT4065A has an enable input EN for turning

the IC on or off. When EN is less than 0.7V, the IC

is in 8μA low current shutdown mode . When EN is

higher than 0.8V, the IC is in normal operation

mode. EN is internally pulled up with a 4μA current

source and can be left unconnected for always-on

operation. EN should never be directly connected to

IN.

Thermal Shutdown

The ACT4065A automatically turns off when its

junction temperature exceeds 155°C.