Datasheet
ADP2302/ADP2303 Data Sheet
Rev. A | Page 18 of 28
response and efficiency. Therefore, the inductor value is calculated
using the following equation:
DIN
D
OUT
sw
LOAD
OUT
IN
VV
VV
fI
VV
L
(max)
3.0
where I
LOAD(max)
is the maximum load current.
The inductor peak current is calculated using the following
equation:
2
(max)
RIPPLE
LOAD
PEAK
I
II
The minimum current rating of the inductor must be greater
than the inductor peak current. For ferrite core inductors with a
quick saturation characteristic, the inductor saturation current
rating should be higher than the switch current limit threshold
to prevent the inductor from reaching its saturation point. Be
sure to validate the worst-case condition, in which there is a
shorted output, over the intended temperature range.
Inductor conduction loss is caused by the flow of current
through internal dc resistance (DCR). Larger sized inductors
have smaller DCR of the inductor and, therefore, may reduce
inductor conduction losses. Inductor core loss is related to the
core material and the ac flux swing, which are affected by the
peak-to-peak inductor ripple current. Because the ADP2302/
ADP2303 are high frequency switching regulators, shielded fer-
rite core materials are recommended for their low core losses
and low EMI. Some recommended inductors are shown in
Table 8.
CATCH DIODE
The catch diode conducts the inductor current during the off
time of the internal MOSFET. The average current of the diode
in normal operation is, therefore, dependent on the duty cycle
of the regulator as well as the output load current.
(max))(
1
LOAD
DIN
D
OUT
AVGDIODE
I
VV
VV
I
where V
D
is the diode forward drop.
The only reason to select a diode with a higher current rating
than necessary in normal operation is for the worst-case condi-
tion, in which there is a shorted output. In this case, the diode
current increases up to the typical peak current limit threshold.
Be sure to consult the diode data sheet to ensure that the diode
can operate well within the thermal and electrical limits.
The reverse breakdown voltage rating of the diode must be higher
than the highest input voltage and allow an appropriate margin
for the ringing that may be present on the SW node. A Schottky
diode is recommended for the best efficiency because it has a
low forward voltage drop and fast switching speed. Table 7
provides a list of recommended Schottky diodes.
Table 7. Recommended Schottky Diodes
Vendor Part No. V
RRM
(V) I
AVG
(A)
Vishay SSB43L 30 4
SSA33L 30 3
ON Semiconductor MBRS330T3 30 3
Diodes Inc. B330B 30 3
Table 8. Recommended Inductors
Vendor Value (μH) Part No. DCR (mΩ) I
SAT
(A) Dimensions L × W × H (mm)
Sumida 2.5 CDRH104RNP-2R5N 7.8 7.5 10.5 × 10.3 × 3.8
3.8 CDRH104RNP-3R8N 9.6 6 10.5 × 10.3 × 3.8
5.2 CDRH104RNP-5R2N 16 5.5 10.5 × 10.3 × 3.8
7 CDRH104RNP-7R0N 20 4.8 10.5 × 10.3 × 3.8
10 CDRH104RNP-100N 26 4.4 10.5 × 10.3 × 3.8
Coilcraft 2.5 MSS1038-252NL 10 7.62 10 × 10.2 × 3.8
3.8 MSS1038-382NL 13 6.5 10 × 10.2 × 3.8
5.2 MSS1038-522NL 22 5.28 10 × 10.2 × 3.8
7 MSS1038-702NL 27 4.74 10 × 10.2 × 3.8
10 MSS1038103NL 35 3.9 10 × 10.2 × 3.8
Toko 2.8 #919AS-2R8M 10.7 8.3 10.3 × 10.3 × 4.5
3.7 #919AS-3R7M 14.2 7 10.3 × 10.3 × 4.5
4.7 #919AS-4R7M 16.2 6.1 10.3 × 10.3 × 4.5
6.4 #919AS-6R4M 22.9 5.2 10.3 × 10.3 × 4.5
10 #919AS-100M 26.5 4.3 10.3 × 10.3 × 4.5
TDK 2.2 VLF10040T-2R2N7R1 7.9 8.2 10 × 9.7 × 4.0
3.3 VLF10040T-3R3N6R2 10.5 6.7 10 × 9.7 × 4.0
4.7 VLF10040T-4R7N5R4 12.7 5.4 10 × 9.7 × 4.0
6.8 VLF10040T-6R8N4R5 19.8 4.6 10 × 9.7 × 4.0
10 VLF10040T-100M3R8 28 3.8 10 × 9.7 × 4.0