ACT4528

Innovative Power

TM

- 6 -

www.active-semi.com

Copyright

©

2

0

1

5

-2017 Active-Semi, Inc.

Rev 2, 06-Jan-2016

FUNCTIONAL BLOCK DIAGRAM

FUNCTIONAL DESCRIPTION

Output Current Sensing and Regulation

Sense resistor is connected to CSP and CSN. The

sensed differential voltage is compared with interval

reference to regulate current. CC loop and CV loop

are in parallel. The current loop response is allowed

to have slower response compared to voltage loop.

However, during current transient response, the

inductor current overshoot/undershoot should be

controlled

within

+/-25%

to

avoid

inductor

saturation.

Cycle-by-Cycle Current Control

The conventional cycle-by-cycle peak current mode

is implemented with high-side FET current sense.

Input Over Voltage Protection

The converter is disabled if the input voltage is

above 42V (+/-2V). Device resumes operation

automatically 40ms after OVP is cleared.

Output Over Voltage Protection

Device stops switching when output over-voltage is

sensed, and resumes operation automatically when

output voltage drops to OVP- hysteresis.

Output Over Voltage Discharge

Discharge circuit starts to discharge output through

CSP pins when output over voltage is detected.

Discharge circuit brings 12V down to 5V in less

than 100ms.

Output Under-Voltage Protection /

Hiccup Mode

There

is

a

under

voltage

protection

(UVP)

threshold. If the UVP threshold is hit for 10us, an

over current or short circuit is assumed, and the

converter goes into hiccup mode by disabling the

converter and restarts after hiccup waiting period.

Cord Compensation

In

some

applications,

the

output

voltage

is

increased with output current to compensate the

potential voltage drop across output cable. The

compensation is based on the high side feedback

resistance.

The compensation voltage is derived as:

Ä

Where K=3.03

This voltage difference could be added on the

sink current at FB pin to pull Vout higher than

programmed voltage.

The cord compensation loop should be very slow to

avoid potential disturbance to the voltage loop. The

voltage loop should be sufficiently stable on various

cord compensation setting.

Thermal Shutdown

°

C

,

A

C

T

4

5

2

8

g

o

e

s

drops by 30

°

C

.

PWM

Controller

Driver

Current Sense

and Control

70m

Ω

4.7

Ω

OVP

CSP

CSN

GND

SW

HSB

UVLO

VIN

DP

DM

QC2.0

Detect

USB

Auto

Detect