Datasheet

Data Sheet ADP2503/ADP2504
Rev. C | Page 13 of 16
APPLICATIONS INFORMATION
ADIsimPower DESIGN TOOL
The ADP2503/ADP2504 is supported by ADIsimPower design
tool set. ADIsimPower is a collection of tools that produce
complete power designs optimized for a specific design goal.
The tools enable the user to generate a full schematic, bill of
materials, and calculate performance in minutes. ADIsimPower
can optimize designs for cost, area, efficiency, and parts count
while taking into consideration the operating conditions and
limitations of the IC and all real external components. For
more information about ADIsimPower design tools, refer to
www.analog.com/ADIsimPower. The tool set is available from
this website, and users can also request an unpopulated board
through the tool.
INDUCTOR SELECTION
The high 2.5 MHz switching frequency of the ADP2503/
ADP2504 allows for minimal output voltage ripple, while
minimizing inductor size and cost. Careful inductor selection
also optimizes efficiency and reduces electromagnetic interfe-
rence (EMI). The selection of the inductor value determines
the inductor current ripple and loop dynamics.
LfV
VVV
BuckpeakI
OSC
IN
OUT
IN
OUT
L
××
−×
=∆
)(
)(,
Lf
V
V
VV
BoostpeakI
OSC
IN
OUT
IN
OUT
L
×
×
−
=∆
)(
)(,
where:
f
OSC
is the switching frequency (typically 2.5 MHz).
L is the inductor value in henries.
A larger inductor value reduces the current ripple (and, therefore,
the peak inductor current), but is physically larger in size with
increased dc resistance. Inductor values between 1 µH and
1.5 µH are suggested. The maximum inductor value to ensure
stability is 2.0 µH. For increased efficiency with the ADP2504,
it is suggested that a 1.5 µH inductor be used.
The inductor peak current is at the maximum in boost mode.
To determine the actual maximum inductor current in boost
mode, the input dc current should be estimated.
ηV
V
II
IN
OUT
MAXLOADMAXIN
1
)()(
×








×=
where η is efficiency (assume η ≈ 0.85 to 0.90).
The saturation current rating of the inductor must be at least
I
IN(MAX)
+ ΔI
LOAD
/2.
Ceramic multilayer inductors can be used with lower current
designs for a reduced overall solution size and dc resistance
(DCR). These are available in low profile packages. Care must
be taken because these derate quickly as the inductor value is
increased, especially at higher operating temperatures.
Ferrite core inductors have good core loss characteristics as well as
reasonable dc resistance. A shielded ferrite inductor reduces the
EMI generated by the inductor.
Table 5. Sample of Recommended Inductors
Vendor
Value
(µH) Part No.
DCR
(mΩ)
I
SAT
(A)
Dimensions
L × W × H
(mm)
Toko 1.2 DE2810C 55 1.7 2.8 × 2.8 × 1.0
Toko 1.5 DE2810C 60 1.5 2.8 × 2.8 × 1.0
Toko
1
MDT2520-CN
100
1.8
2.5 × 2 × 1.2
Murata 1 LQM2HP-G0 55 1.6 2.5 × 2 × 1
Murata 1.5 LQM2HP-G0 70 1.5 2.5 × 2 × 1
TDK 1.0 CPL2512T 90 1.5 2.5 × 1.5 × 1.2
TDK 1.5 CPL2512T 120 1.2 2.5 × 1.5 × 1.2
Coilcraft 1.0 LPS3010 85 1.7 3.0 × 3.0 × 0.9
Coilcraft 1.5 LPS3010 120 1.3 3.0 × 3.0 × 0.9
Taiyo
Yuden
1.5 NR3015T1 40 1.5 3.0 × 3.0 × 1.5
Output Capacitor Selection
The output capacitor selection determines the output voltage
ripple, transient response, and the loop dynamics of the
ADP2503/ADP2504. The output voltage ripple for a given
output capacitor is as follows:
( )
OUT
OSC
IN
OUT
IN
OUT
OUT
CfLV
VVV
BuckpeakV
××××
−×
=∆
2
8
)(
)(,
OSC
OUTOUT
IN
OUT
LOAD
OUT
fVC
VVI
BoostpeakV
××
−×
=∆
)(
)(,
If the ADP2503/ADP2504 are operating in buck mode, the
worst-case voltage ripple occurs for the highest input voltage,
V
IN
. If the ADP2503/ADP2504 are operating in boost mode, the
worst-case voltage ripple occurs for the lowest input voltage, V
IN
.
The maximum voltage overshoot, or undershoot, is inversely
proportional to the value of the output capacitor. To ensure
stability and excellent transient response, it is recommended
to use a minimum of 22 µF X5R 6.3 V or 2 × 10 µF X5R 6.3 V
capacitors at the output. The effective capacitance (includes
temperature and dc bias effects) needed for stability is 14 µF.