ACT6390(2007) Ver la hoja de datos (PDF) - Active-Semi, Inc
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ACT6390 Datasheet PDF : 11 Pages
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FUNCTIONAL BLOCK DIAGRAM
ACT6390/ACT6391
Rev PrA, 01-Sep-07
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-
grammed by connecting a capacitor (CSS) between
SS and G. Operation of the soft-start function is as
follows: when the IC is disabled, SS is actively dis-
charged to G. Upon enabling the IC, CSS is charged
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:
t SS 2.2 10 5 C SS
(1)
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:
R1
R
2
VOUT
VFB
1
(2)
Where VFB is 1.24V.
Innovative Products. Active Solutions.
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www.active-semi.com
Copyright © 2007 Active-Semi, Inc.
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