ADP3207 ANALOG DEVICES, ADP3207 Datasheet - Page 21

• Manufacturer Part Number: ADP3207
• Description: 7-Bit Programmable Multiphase Mobile CPU Synchronous Buck Controller
• Manufacturer: ANALOG DEVICES

Solving Equation 6 for a 20 mV peak-to-peak output ripple
voltage yields
If the ripple voltage ends up being less than the initially selected
value, then the inductor can be changed to a smaller value until
the ripple value is met. This iteration allows optimal transient
response and minimum output decoupling.
The smallest possible inductor should be used to minimize the
number of output capacitors. For this example, choosing a
360 nH inductor is a good starting point, and gives a calculated
ripple current of 10.7 A. The inductor should not saturate at the
peak current of 27.4 A, and should be able to handle the sum of
the power dissipation caused by the average current of 16 A in
the winding and core loss.
Another important factor in the inductor design is the DCR,
which is used to measure phase currents. A large DCR causes
excessive power losses, though too small a value leads to
increased measurement error. This example uses an inductor
with a DCR of 0.89 mΩ.
Selecting a Standard Inductor
Once the inductance and DCR are known, the next step is to
either design an inductor or select 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 keep the accuracy of the system controlled; 20%
inductance and 15% DCR (at room temperature) are reasonable
assumptions that most manufacturers can meet.
Power Inductor Manufacturers
The following companies provide surface mount power
inductors optimized for high power applications upon request:
•
•
•
•
Vishay Dale Electronics, Inc.
http://www.vishay.com
Panasonic
http://www.panasonic.com
Sumida Corporation
http://www.sumida.com
NEC Tokin Corporation
http://www.nec-tokin.com
L
≥
. 1
150
V
×
2
1 .
m
280
Ω
×
kHz
(
1
−
×
(
2
20
×
. 0
mV
061
)
)
×
(
1
−
. 0
061
)
=
356
nH
Rev. 0 | Page 21 of 32
Output Droop Resistance
The inductor 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 the currents of the
resistors monitoring the voltage across each inductor and by
passing the signal through a low-pass filter. This summer-filter
is implemented by the CS amplifier that is configured with
resistors R
resistance of the regulator is set by the following equations,
where R
Users have the flexibility of choosing either R
the current drive ability of the CSCOMP pin, the R
should be larger than 100 kΩ. For example, users should
initially select R
solve for C
Because C
with two standard capacitors in parallel: 1.8 nF and 47 pF. For
the best accuracy, C
Next, solve R
The standard 1% resistor for R
Inductor DCR Temperature Correction
With the inductor DCR used as a sense element, and copper
wire being the source of the DCR, users need to compensate for
temperature changes in the inductor’s winding. Fortunately,
copper has a well-known temperature coefficient (TC) of
0.39%/°C.
If R
change in resistance, then it cancels the temperature variation of
the inductor DCR. Due to the nonlinear nature of NTC
thermistors, series resistors, R
needed to linearize the NTC and produce the desired
temperature coefficient tracking.
CS
C
C
R
R
is designed to have an opposite sign but equal percentage
CS
O
CS
PH
L
=
( X
=
=
is the DCR of the output inductors:
CS
)
PH(X)
R
CS
R
. 0
≥
R
PH
L
89
is not the standard capacitance, it is implemented
O
CS
PH(X)
×
. 0
(
).
L
2
X
m
R
(summer), and R
)
89
1 .
CS
360
CS
×
Ω
m
by rearranging Equation 7.
m
R
to be equal to 220 kΩ, then use Equation 8 to
×
Ω
nH
L
Ω
CS
220
should be a 5% NPO capacitor.
×
220
k
Ω
k
Ω
=
CS1
. 1
PH(X)
=
84
CS
93
and R
nF
and C
2 .
is 93.1 kΩ.
k
Ω
CS2
CS
www.DataSheet4U.com
(see Figure 11) are
(filter). The output
CS
or R
ADP3207
CS
PH(X)
resistance
. Due to
(7)
(8)