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ACT4523AYH-T

Wide-Input Sensorless CC/CV Step-Down DC/DC Converter

Active-Semi, Inc 

FUNCTIONAL BLOCK DIAGRAM

ACT4523A

Rev 0, 25-Jul-13

FUNCTIONAL DESCRIPTION

CV/CC Loop Regulation

As seen in Functional Block Diagram, the

ACT4523A 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.

regulating output voltage to regulating output

current, and the output voltage will drop with

increasing load.

The Oscillator normally switches at 250kHz.

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

switching frequency decreases until it reaches a

typical value of 36kHz at VFB = 0.15V.

Over Voltage Protection

The ACT4523A has an OVP pin. If the voltage at this

pin exceeds 0.8V, the IC shuts down high side switch.

Thermal Shutdown

The ACT4523A disables switching when its junction

temperature exceeds 155°C and resumes when the

temperature has dropped by 25°C.

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

pin is charged to VSW + 5V when the Low-Side

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

Innovative PowerTM

-5-

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