ACT6390/ACT6391

Rev 1, 22-Aug-13

- 5 -

www.active-semi.com

Copyright © 2013 Active-Semi, Inc.

FUNCTIONAL BLOCK DIAGRAM

FUNCTIONAL DESCRIPTION

The ACT6390 and ACT6391 are highly efficient

step-up DC/DC converters that employ a current-

mode, fixed frequency pulse-width modulation

(PWM) architecture with excellent line and load

regulation.

The ACT6390 and ACT6391 operate at constant

switching frequency under medium to high load cur-

rent conditions. At light loads, these devices oper-

ate in a pulse-skipping mode in order to improve

light-load efficiency.

Soft-Start

The ACT6390 and ACT6391 both offer a program-

mable soft-start function which minimizes inrush

current during startup. The soft-start period is pro-

SS and G. Operation of the soft-start function is as

follows: when the IC is disabled, SS is actively dis-

with a 4.5µA current so that the voltage at SS in-

creases in a controlled manner. The peak inductor

current is limited by the voltage at SS, so that the

input current is limited until the soft-start period ex-

pires, and the regulator can achieve its full output

current rating.

The soft-start period can be calculated as a simple

function of the soft-start capacitor using the equa-

tion:

Frequency Selection

The ACT6390 and ACT6391 include a pin-

selectable operating frequency drive FREQ to a

logic high for 1.3MHz operation, drive FREQ to a

logic low for 700kHz operation.

Selectable operating frequency, in combination with

the external compensation network, allows a wide

range of flexibility in optimizing total solution size

and cost.

FREQ is internally pulled down by 5.5µA, this pin

may be left unconnected to achieve a 700kHz oper-

ating frequency.

Setting the Output Voltage

The ACT6390 and ACT6391 both feature external

adjustable output voltages of up to 12V. To program

the output voltage, simply connect a resistive volt-

age divider between the output, FB, and G, with

resistors set according to the following equation:

SS

5

SS

C

10

2

.

2

t

×

×

=

⎥

⎦

⎤

⎢

⎣

⎡

−

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

×

=

1

V

V

2

R

1

R

FB

OUT

5.5µA

4.5µA

-

+

IN

SS

SW

G

FREQ

FB

COMP

EN

OSCILLATOR

SLOPE

COMPENSATION

CONTROL

AND

DRIVE

LOGIC

SOFT

START

ERROR

COMPARATOR

CLOCK

CURRENT SENSE

AMPLIFIER

+

ERROR

AMPLIFIER

1.24V

(1)

(2)