ADP3168JRUZ-REEL AD [Analog Devices], ADP3168JRUZ-REEL Datasheet - Page 15

• Manufacturer Part Number: ADP3168JRUZ-REEL
• Description: 6-Bit, Programmable 2-, 3-, 4-Phase Synchronous Buck Controller
• Manufacturer: AD [Analog Devices]

DESIGNING AN INDUCTOR
Once the inductance and DCR are known, the next step is to
either design an inductor or find a standard inductor that
comes as close as possible to meeting the overall design goals.
It is also important to have the inductance and DCR tolerance
specified to control the accuracy of the system. 15% inductance
and 8% DCR (at room temperature) are reasonable tolerances
that most manufacturers can meet.
The first decision in designing the inductor is to choose the
core material. There are several possibilities for providing low
core loss at high frequencies. Two examples are the powder
cores (e.g., Kool-Mµ® from Magnetics, Inc. or Micrometals)
and the gapped soft ferrite cores (e.g., 3F3 or 3F4 from Philips).
Low frequency powdered iron cores should be avoided due to
their high core loss, especially when the inductor value is
relatively low and the ripple current is high.
The best choice for a core geometry is a closed-loop type such
as a pot core, PQ, U, or E core or toroid. A good compromise
between price and performance is a core with a toroidal shape.
There are many useful references for quickly designing a power
inductor, such as the following:
SELECTING A STANDARD INDUCTOR
The companies listed below can provide design consultation
and deliver power inductors optimized for high power
applications upon request.
Power Inductor Manufacturers
•
•
•
•
•
•
Coilcraft
[phone]
www.coilcraft.com
Coiltronics
[phone]
www.coiltronics.com
Sumida Electric Company
[phone]
www.sumida.com
Vishay Intertechnology
[phone]
www.vishay.com
Magnetic Designer Software
Intusoft (www.intusoft.com)
Designing Magnetic Components for High-Frequency
DC-DC Converters, by William T. McLyman, Kg
Magnetics, Inc., ISBN 1883107008
Rev. B | Page 15 of 24
OUTPUT DROOP RESISTANCE
The design requires that the regulator output voltage measured
at the CPU pins drops when the output current increases. The
specified voltage drop corresponds to a dc output resistance (R
The output current is measured by summing together the
voltage across each inductor and passing the signal through a
low-pass filter. This summer filter is the CS amplifier config-
ured with resistors R
The output resistance of the regulator is set by the following
equations, where R
One has the flexibility of choosing either R
to select R
rearranging Equation 6.
Next, use Equation 6 to solve for C
It is best to have a dual location for C
values can be used in parallel to get as close to the value desired.
For this example, choosing C
parallel is a good choice. For best accuracy, C
or 10% NPO capacitor. The closest standard 1% value for R
is 124 kΩ.
C
C
R
R
R
O
CS
PH
PH
CS
=
=
( )
( )
=
x
CS
R
x
R
R
PH
1
=
L
equal to 100 kΩ, and then solve for R
CS
=
6 .
×
( )
1
1
L
x
R
R
R
6 .
3 .
m
O
×
CS
600
L
Ω
m
m
R
L
×
Ω
Ω
L
×
is the DCR of the output inductors:
PH(X)
R
nH
100
CS
×
100
(summers), and R
k
Ω
k
CS
Ω
=
to be 1.5 nF and 2.2 nF in
. 3
=
75
123
CS
.
nF
CS
k
in the layout so standard
Ω
CS
CS
or R
and C
CS
should be a 5%
PH(X)
PH(X)
ADP3168
CS
(filter).
. It is best
by
(6)
(7)
PH(X)
O
).