Datasheet

ADP2125
Rev. A | Page 12 of 16
APPLICATIONS INFORMATION
The ADP2125 is designed to be compatible with chip inductors
and multilayer ceramic capacitors that are ideal for their small
footprint and low height. The recommended components for
this application may change as this technology advances. Table 5,
Table 6, and Table 7 list compatible inductors and capacitors.
This section describes the selection of external components.
The component value ranges are limited to optimize efficiency
and transient performance while maintaining stability over the
full operating range.
INDUCTOR SELECTION
The high switching frequency of the ADP2125 allows for minimal
output voltage ripple, even with small inductors. Inductor sizing
is a trade-off between efficiency and transient response. A small
value inductor leads to a larger inductor current ripple that
provides excellent transient response, but degrades efficiency. A
small footprint and low height chip inductor can be used for an
overall smaller solution size but has a higher dc resistance (DCR)
value and lower current rating that can degrade performance.
Shielded ferrite core inductors are recommended for their low
core losses and low electromagnetic interference (EMI). The
recommended inductor for the ADP2125 is 1.5 µH.
The inductor peak-to-peak current ripple, I
L
, can be calculated as
follows:
(
)
SW
IN
OUT
IN
OUT
L
fLV
VVV
I
××
−×
=Δ
(2)
It is important that the inductor be capable of handling the
maximum peak inductor current, I
PK
, determined by the
following equation:
I
PK
= I
LOAD(MAX)
+ I
L
/2 (3)
The dc current rating of the inductor should be greater than the
calculated I
PK
to prevent core saturation.
INPUT CAPACITOR SELECTION
The input capacitor must be rated to support the maximum
input operating voltage. Higher value input capacitors reduce
the input voltage ripple caused by the switch currents on the
VIN pin. Maximum rms input current for the application can
be calculated using the following equation:
()
IN
OUT
IN
OUT
MAXLOADCINMAXRMS
V
VVV
II
−×
×=
)()(_
(4)
Place the input capacitor as close as possible to the VIN pin to
minimize supply noise.
In principle, different types of capacitors can be considered, but
for battery-powered applications, the best choice is the multi-
layer ceramic capacitor, due to its small size, low equivalent
series resistance (ESR), and low equivalent series inductance (ESL).
It is recommended that the VIN pin be bypassed with a 2.2 µF
input capacitor. The input capacitor can be increased without any
limit for better input voltage filtering. X5R or X7R dielectrics with
a voltage rating of 6.3 V or higher are recommended.
Table 5. Inductor Selection
Manufacturer Series Inductance (µH) DCR (mΩ) (typ) Current Rating (mA) Size (L × W × H) (mm) Package
Murata LQM18PN1R8NC0L 1.80 240 700 1.60 × 0.80 × 0.55 0603
LQM18PN1R5NB0L 1.50 350 600 1.60 × 0.80 × 0.40 0603
Taiyo Yuden CKP1608L1R5M 1.50 220 700 1.60 × 0.80 × 0.55 0603
Table 6. Input Capacitor Selection
Manufacturer Part Number Capacitance (F) Voltage Rating (V)
Temperature
Coefficient
Size (L × W × H) (mm) Package
Murata GRM155R60J225ME95 2.2 6.3 X5R 1.0 × 0.5 × 0.5 0402
Taiyo Yuden JMK105BJ225MV-F 2.2 6.3 X5R 1.0 × 0.5 × 0.5 0402
TDK C1005X5R0J225M 2.2 6.3 X5R 1.0 × 0.5 × 0.5 0402
Table 7. Output Capacitor Selection
Manufacturer Part Numbers Capacitance (F) Voltage Rating (V)
Temperature
Coefficient Size (L × W × H) (mm) Package
Murata GRM155R60J475ME87 4.7 6.3 X5R 1.0 × 0.5 × 0.5 0402
GRM155R60G475ME47 4.7 4 X5R 1.0 × 0.5 × 0.5 0402
Taiyo Yuden AMK105BJ475MV-F 4.7 4 X5R 1.0 × 0.5 × 0.5 0402
TDK C1005X5R0J475M 4.7 6.3 X5R 1.0 × 0.5 × 0.5 0402