ACT6330
Rev0, 02-Apr-08
STEP-UP DC/DC CONVERTER (REG2)
FUNCTIONAL DESCRIPTION CONT’D
Inductor Selection
Rectifier 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.
REG2 requires a Shottky diode to rectify the induc-
tor current. Select a low forward voltage drop Shot-
tky diode with a forward current (IF) rating that is
sufficient to support the maximum switch current
and a sufficient peak repetitive reverse voltage
(VRRM) to support the output voltage.
Optimizing for Smallest Footprint
PCB Layout Considerations
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.
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.
Optimizing for Highest Efficiency
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.
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.
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.
Table 1:
Recommended Inductance Values
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)
10
9
12
18
15
22
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.
Innovative PowerTM
ActivePMUTM is a trademark of Active-Semi.
- 12 -
www.active-semi.com
Copyright © 2008 Active-Semi, Inc.
ACTIVE-SEMI [ ACTIVE-SEMI, INC ]
