ACT6330

Rev0, 02-Apr-08

STEP-UP DC/DC CONVERTER (REG2)

Innovative Power

TM

- 12 -

www.active-semi.com

Copyright © 2008 Active-Semi, Inc.

ActivePMU

Inductor Selection

REG2 has been designed to provide excellent per-

formance across a wide range of applications, al-

lowing a design to be optimized for both a small

footprint as well as for achieving the highest possi-

ble efficiency.

Optimizing for Smallest Footprint

REG2 is capable of operating with very low inductor

values in order to achieve the smallest possible

footprint . When solution size is of primary concern,

best results are achieved when an inductance value

that ensures discontinuous conduction mode (DCM)

operation over the full load current range is used.

Optimizing for Highest Efficiency

REG2 achieves excellent efficiency in applications

that demand the longest possible battery life. When

efficiency is the primary design consideration, best

results are achieved when an inductance value that

both results in continuous conduction mode (CCM)

operation and achieves a very small inductor ripple

current is chosen. Table 1 provides recommended

inductance values.

Table 1:

Recommended Inductance Values

Output Capacitor Selection

REG2 is designed to operate with output capacitor

ranging from 1µF to 10µF. A 2.2µF output capacitor

is suitable for most applications, although lager out-

put capacitor may be used to minimize output rip-

ple, if need. Ceramic capacitors are recommended

for most applications.

Rectifier Selection

REG2 requires a Shottky diode to rectify the induc-

tor current. Select a low forward voltage drop Shot-

sufficient to support the maximum switch current

and a sufficient peak repetitive reverse voltage

PCB Layout Considerations

High switching frequencies and large peak currents

make PC board layout a very important part of the

design. Good design minimizes excessive EMI on

the feedback paths and voltage gradients in the

ground plane, both of which can result in instability

or regulation errors.

Step-up DC/DCs exhibit continuous input current,

so there is some amount of flexibility in placing vias

in the input capacitor circuit. The input capacitor

should be placed as close as possible to the input

pin for good input voltage filtering.

The inductor, input filter capacitor, rectifier, and out-

put filter capacitor should be connected as close

together as possible, with short, direct, and wide

traces. Avoid using vias in the high-current path. If

vias are unavoidable , use many vias in parallel to

reduce resistance and inductance.

Place all feedback voltage-divider resistor as close

as possible to their respective feedback pins. Con-

nect the ground nodes together in a star configura-

tion, with a direct connection to the exposed pad.

Route high-speed switching nodes away from the

sensitive analog areas. Finally, the exposed pad

should be directly connected to the backside

ground plane using multiple vias to achieve low

electrical and thermal resistance. Note that since

the LED string is a low, DC-current path, it does not

generally require special layout consideration.

Output Voltage (V)

L (µH)

9

10

12

15

18

22

FUNCTIONAL DESCRIPTION CONT’D