ACT4533C
Rev 1, 14-Nov-14
FUNCTIONAL BLOCK DIAGRAM FOR ACT4533C
FUNCTIONAL DESCRIPTION
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.
CV/CC Loop Regulation
As seen in Functional Block Diagram, the
ACT4533C is a peak current mode pulse width
modulation (PWM) converter with CC and CV
control. The converter operates as follows:
The Oscillator normally switches at 125kHz.
However, if FB voltage is less than 0.6V, then the
switching frequency decreases until it reaches a
typical value of 18kHz at VFB = 0.15V.
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.
Over Voltage Protection
The ACT4533C has an OVP pin. If the voltage at
this pin exceeds 0.8V, the IC shuts down high-side
switch.
Thermal Shutdown
The ACT4533C 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
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