Datasheet

ADP2126/ADP2127 Data Sheet
Rev. B | Page 14 of 20
APPLICATIONS INFORMATION
The low-profile ADP2126/ADP2127 are compatible with chip
inductors and multilayer ceramic capacitors that are ideal for
use in portable applications due to their small footprint and low
height. The recommended components for low-profile applications
may change as this technology advances. Table 5 and Table 6 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 ADP2126/ADP2127 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,
which 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 advantageous for their low core
losses and low electromagnetic interference (EMI). For optimal
performance and stability, use inductor values between 1.5 µH
and 0.5 µH. Recommended inductors are shown in Table 5.
The inductor peak-to-peak current ripple, I
L
, is calculated from
(
)
SW
IN
OUT
IN
OUT
L
fLV
VVV
I
××
−×
=Δ
(2)
where:
f
SW
is the switching frequency.
L is the inductor value.
It is important that the minimum dc current rating of the inductor
be greater than the peak inductor current (I
PK
) in the application.
I
PK
is calculated from
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 is calculated using
()
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 multilayer
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 at least a
2.2 µF input capacitor. For a 0.22 mm height solution using the
ADP2127, at least 2 × 1.0 µF capacitors will be necessary on the
input. 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 LQM18PN1R0-A52 1.0 520 500 1.6 × 0.8 × 0.33 0603
Taiyo Yuden CKP1608S1R5M 1.5 420 500 1.6 × 0.8 × 0.33 0603
Table 6. Input/Output Capacitor Selection
Manufacturer Part Number Capacitance (μF) Voltage Rating (V)
Temperature
Coefficient Size (L × W × H) (mm) Package
Murata GRM153R60J225ME95 2.2 ± 20% 6.3 X5R 1.0 × 0.5 × 0.33 0402
GRM153R60G225M 2.2 ± 20% 4 X5R 1.0 × 0.5 × 0.33 0402
Taiyo Yuden JMK105BJ225MP 2.2 ± 20% 6.3 X5R 1.0 × 0.5 × 0.33 0402
AMK105BJ225MP 2.2 ± 20% 4 X5R 1.0 × 0.5 × 0.33 0402
AMK105BJ105MC 1.0 ± 20% 4 X5R 1.0 × 0.5 × 0.22 0402
ADC105BJ105ME 1.0 ± 20% 4 X5R 1.0 × 0.5 × 0.20 0402
JMK105BJ474KC 0.47 ± 10% 6.3 X5R 1.0 × 0.5 × 0.22 0402
JMK105BJ474MC 0.47 ± 20% 6.3 X5R 1.0 × 0.5 × 0.22 0402
TDK CGB2A3X5R0J105K 1.0 ± 10% 6.3 X5R 1.0 × 0.5 × 0.33 0402
CGB2A3X5R0J105M 1.0 ± 20% 6.3 X5R 1.0 × 0.5 × 0.33 0402