Classification | PRIVATE

Data Sheet Rev. B, January 2025 | Subject to change without notice

5 of 19

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ACT4533A/B

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

FUNCTIONAL BLOCK DIAGRAM FOR ACT4533A

FUNCTIONAL BLOCK DIAGRAM FOR ACT4533B

FUNCTIONAL DESCRIPTION

CV/CC Loop Regulation

As seen in Functional Block Diagram, the ACT4533A/B

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 pin is charged

to VSW +5 V when the Low-Side Power Switch turns on.

The COMP voltage is the integration of the error be-

tween

FB

input

and

the

internal

0.808

V

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