NCP1546
The worse case of the diode average current occurs during
The DC current through the inductor is equal to the load
current. The worse case occurs during maximum load
current. Check the vendor’s spec to adjust the inductor value
under current loading. Inductors can lose over 50% of
inductance when it nears saturation.
maximum load current and maximum input voltage. For the
diode to survive the short circuit condition, the current rating
of the diode should be equal to the Foldback Current Limit.
See Table 1 for Schottky diodes from ON Semiconductor
which are suggested for use with the NCP1546 regulator.
The core materials have a significant effect on inductor
performance. The ferrite core has benefits of small physical
size, and very low power dissipation. But be careful not to
operate these inductors too far beyond their maximum
ratings for peak current, as this will saturate the core.
Powered Iron cores are low cost and have a more gradual
saturation curve. The cores with an open magnetic path, such
as rod or barrel, tend to generate high magnetic field
radiation. However, they are usually cheap and small. The
cores providing a close magnetic loop, such as pot−core and
toroid, generate low electro−magnetic interference (EMI).
There are many magnetic component vendors providing
standard product lines suitable for the NCP1546. Table 2
lists three vendors, their products and contact information.
Inductor Selection
When choosing inductors, one might have to consider
maximum load current, core and copper losses, component
height, output ripple, EMI, saturation and cost. Lower
inductor values are chosen to reduce the physical size of the
inductor. Higher value cuts down the ripple current, core
losses and allows more output current. For most
applications, the inductor value falls in the range between
2.2 mH and 22 mH. The saturation current ratings of the
inductor shall not exceed the I , calculated according to
L(PK)
V (V * V )
O
IN
O
)
I
+ I
)
O
L(PK)
2(f )(L)(V
S
IN
Table 1.
Part Number
1N5817
V
(V)
I
(A)
V
(V) @ I
AVERAGE
Package
Axial Lead
Axial Lead
Axial Lead
SOD−123
SOD−123
SOD−123
SMB
BREAKDOWN
AVERAGE
(F)
20
1.0
0.45
0.55
0.6
1N5818
30
40
20
30
40
20
30
40
1.0
1.0
0.5
0.5
0.5
1.0
1.0
1.0
1N5819
MBR0520
MBR0530
MBR0540
MBRS120
MBRS130
MBRS140
0.385
0.43
0.53
0.55
0.395
0.6
SMB
SMB
Table 2.
Vendor
Product Family
UNI−Pac1/2: SMT, barrel
Web Site
Telephone
Coiltronics
www.coiltronics.com
(516) 241−7876
THIN−PAC: SMT, toroid, low profile
CTX: Leaded, toroid
Coilcraft
DO1608: SMT, barrel
DS/DT 1608: SMT, barrel, magnetically shielded
DO3316: SMT, barrel
DS/DT 3316: SMT, barrel, magnetically shielded
DO3308: SMT, barrel, low profile
www.coilcraft.com
(800) 322−2645
(619) 674−8100
Pulse
−
www.pulseeng.com
ORDERING INFORMATION
Device
†
Package
Shipping
NCP1546MNR2G
DFN18
(Pb−Free)
2500 Units / Tape & Reel
†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
http://onsemi.com
12
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