LTC3523/LTC3523-2
10
3523fb
frequency ferrite core inductor materials reduce frequency
dependent power losses compared to cheaper powdered
iron types, improving effi ciency. The inductor should have
low ESR (series resistance of the windings) to reduce the
I
2
R power losses, and must be able to handle the peak
inductor current without saturating. Molded chokes and
some chip inductors usually do not have enough core to
support the peak inductor currents of 1000mA seen on
the LTC3523/LTC3523-2. To minimize radiated noise, use
a toroid, pot core or shielded bobbin inductor. See Table
1 for suggested inductors and suppliers.
Step-Up: For the step-up converter a minimum inductance
value of 3.3μH is recommended for 3.6V and lower output
voltage applications, and a 4.7μH for output voltages
greater than 3.6V. Larger values of inductance will allow
greater output current capability by reducing the inductor
ripple current. Increasing the inductance above 10μH will
increase size while providing little improvement in output
current capability.
Step-Down: For most applications, the value of the inductor
will fall in the range of 3.3μH to 10μH, depending upon
the amount of current ripple desired. A reasonable point
to start is to set the current ripple at 30% of the output
current.
Note that larger values of inductance will allow greater
output current capability by reducing the inductor ripple
current. Increasing the inductance above 10μH will increase
size while providing little improvement in output current
capability. A 4.7μH inductor will work well for most Li-Ion
or 2-cell alkaline/NiMH cell applications
Output and Input Capacitor Selection
Low ESR (equivalent series resistance) capacitors should
be used to minimize the output voltage ripple. Multilayer
ceramic capacitors are an excellent choice as they have
extremely low ESR and are available in small footprints.
Step-Up: A 2.2μF to 10μF output capacitor is suffi cient for
most applications. Larger values up to 22μF may be used
to obtain extremely low output voltage ripple and improve
transient response. An additional phase lead capacitor con-
nected between V
OUT
and FB1 may be required with output
capacitors larger than 10μF to maintain acceptable phase
margin. X5R and X7R dielectric materials are preferred
for their ability to maintain capacitance over wide voltage
and temperature ranges.
Step-Down: Low ESR input capacitors reduce input
switching noise and reduce the peak current drawn from
the battery. It follows that ceramic capacitors are also a
good choice for input decoupling and should be located
as close as possible to the device. Table 2 shows the
range of acceptable capacitors for a given programmed
output voltage. Minimum capacitance values in the table
APPLICATIONS INFORMATION
Table 1. Recommended Inductors
PART L (μH)
MAXIMUM CURRENT
(mA) DCR (Ω)
DIMENSIONS (mm)
(L × W × H) MANUFACTURER
ME3220 4.7 to 15 1200 to 700 0.19 to 0.52
3.2 × 2.5 × 2.0
Coil Craft
www.coilcraft.com
LPS3010 4.7 to 10 720 to 510 0.3 to 0.54
3.0 × 3.0 × 1.0
DO2010 4.7 to 15 800 to 510 0.8 to 1.84
2.0 × 2.0 × 1.0
SD3112 4.7 to 15 740 to 405 0.25 to 0.65
3.1 × 3.1 × 1.2
Cooper
www.cooperet.com
MIP3226D 4.7 to 10 600 to 200 0.1 to 0.16
3.2 × 2.6 × 1.0
FDK
www.fdk.com
LQH32CN 4.7 to 15 650 to 300 0.15 to 0.58
3.2 × 2.5 × 1.5
Murata
www.murata.com
LQH2MC 4.7 to 15 300 to 200 0.8 to 1.6
2 × 1.6 × 0.9
CDRH3D16 4.7 to 15 900 to 450 0.11 to 0.29
3.8 × 3.8 × 1.8
Sumida
www.sumida.com
CDRH2D14 4.7 to 12 680 to 420 0.12 to 0.32
3.2 × 3.2 × 1.5
NR3010 4.7 to 15 750 to 400 0.19 to 0.74
3.0 × 3.0 × 1.0
Taiyo Yuden
www.t-yuden.com
NR3015 4.7 to 15 1000 to 560 0.12 to 0.36
3.0 × 3.0 × 1.5
