ACT6305 datasheet(8/10 Pages) ACTIVE-SEMI

8 / 10 page

ACT6305

Rev 3, 15-Nov-12

Innovative Power

- 8 -

www.active-semi.com

APPLICATIONS INFORMATION

Output Voltage Selection

The ACT6305 provides fixed output voltage options

of 3.3V or 5V, or the output voltage may be ad-

justed over a 2V to 5V range by connecting an

external resistive voltage divider. When Output Volt-

age is set by external resistive voltage divider, add

a 47pF to 150pFcapacitor as feedforward capacitor

(CFF) as shown in Figure 1.

Table 1:

Output Voltage Programming

Figure 1:

Output Voltage Setting

Output Capacitor Selection

A minimum value of output capacitance is required

to maintain loop stability and normal operation of

the IC. The output capacitor value should be in the

range of 22µF to 100µF. To obtain small output rip-

ple, use a large capacitor with low ESR. Ceramic

capacitors should be used for highest performance.

If a tantalum capacitor is used, choose only low

ESR types and a smaller low ESR capacitor of

about 1µF can be connected in parallel to filter high

frequency noise.

Inductor Selection

For most applications, the inductor value should be

in the range of 4.7µH to 22µH. Smaller inductors

provide faster load transient response and have a

smaller physical size, but they also result in higher

ripple current and reduce the maximum available

output current. Choose inductors with low series

resistance to obtain the highest efficiency.

Board Layout

To reduce noise and increase efficiency, high cur-

rent traces should be wide and direct, and an ex-

tended ground plane should be used. Switching

current paths should be laid out as tightly as possi-

ble, with the inductor and input and output capaci-

tors located close to the IC in order to reduce elec-

tromagnetic radiation.

If an external resistor divider is used, place the re-

sistors very close to the FB and G pins, and keep

them away from the high switching current paths.

FB = OUT

VOUT = 3.3V

FB = G

VOUT = 5V

FB connect to resistive

divider

VOUT = 1.18V (1 + RFB1/RFB2)

ACT6305

VOUT

RFB1

RFB2

OUT

CFF

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