ACT4523

Rev 7, 01-Aug-13

Innovative Power

TM

- 5 -

www.active-semi.com

Copyright © 2013 Active-Semi, Inc.

FUNCTIONAL BLOCK DIAGRAM

FUNCTIONAL DESCRIPTION

CV/CC Loop Regulation

As seen in Functional Block Diagram, the ACT4523

is a peak current mode pulse width modulation

(PWM) converter with CC and CV control. The

converter operates as follows:

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

connected to IN, the inductor current ramps up to

store energy in the magnetic field. The inductor

current level is measured by the Current Sense

Amplifier and added to the Oscillator ramp signal. If

the resulting summation is higher than the COMP

voltage, 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.

At this point, the SW side of the inductor swings to

a diode voltage below ground, causing the inductor

current to decrease and magnetic energy to be

transferred to output. This state continues until the

cycle starts again. The High-Side Power Switch is

driven by logic using HSB as the positive rail. This

Power Switch turns on. The COMP voltage is the

integration of the error between FB input and the

internal 0.808V reference. If FB is lower than the

reference voltage, COMP tends to go higher to

increase current to the output. Output current will

increase until it reaches the CC limit set by the ISET

resistor. At this point, the device will transition from

regulating output voltage to regulating output

current, and the output voltage will drop with

increasing load.

The Oscillator normally switches at 225kHz.

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

switching frequency decreases until it reaches a

Enable Pin

The ACT4523 has an enable input EN for turning

the IC on or off. The EN pin contains a precision

1.6V comparator with 125mV hysteresis and a 4µA

pull-up current source. The comparator can be used

voltage higher than the normal UVLO value. It can

charging of a deeply discharged battery, or it can be

used with a resistor divider containing a thermistor

to

provide

a

temperature-dependent

shutoff

protection for over temperature battery. The

thermistor should be thermally coupled to the

battery pack for this usage.

If left floating, the EN pin will be pulled up to roughly

5V by the internal 4µA current source. It can be

driven from standard logic signals greater than

1.6V, or driven with open-drain logic to provide

digital on/off control.

Thermal Shutdown

The ACT4523 disables switching when its junction

temperature exceeds 150°C and resumes when the

temperature has dropped by 20°C.

EN

FB

BANDGAP,

REGULATOR,

&

SHUTDOWN

CONTROL

+

-

OSCILLATOR

EMI

CONTROL

PWM

CONTROLLER

CC

CONTROL

SW

HSB

IN

AVIN

PVIN

Σ

COMP

ISET