ACT4533A datasheet(6/18 Pages) ACTIVE-SEMI

6 / 18 page

ACT4533A/B

Rev 0, 14-Aug-13

Innovative Power

- 6 -

www.active-semi.com

FUNCTIONAL DESCRIPTION

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

regulating output voltage to regulating output

current, and the output voltage will drop with

increasing load.

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.

Over Voltage Protection (ACT4533A)

The ACT4533A has an OVP pin. If the voltage at

this pin exceeds 0.8V, the IC shuts down high-side

switch. There is a 4µA pull-up current at this pin.

EN/OVP Pin (ACT4533B)

The ACT4533B has an enable input and OVP input

for turning the IC on and off.

If the voltage at this pin rises above 0.65V, the IC is

enabled. The EN contains a 60mV hysteresis and

4µA pull-up current source.

If the voltage at this pin is between 0.65V and

2.26V, the IC operates normally; if the voltage at

this pin exceeds 2.26V, the IC shuts down high-side

switch. The OVP contains a 500mV hysteresis and

4µA pull-up current source.

Thermal Shutdown

The ACT4533A/B disables switching when its

junction temperature exceeds 155°C and resumes

when the temperature has dropped by 25°C.

ACT4533A Datasheet(PDF) 6 Page - Active-Semi, Inc