FAN5018BMTCX Fairchild Semiconductor, FAN5018BMTCX Datasheet - Page 20

• Manufacturer Part Number: FAN5018BMTCX
• Description: IC CTRLR DC-DC MULTIPH 28TSSOP
• Manufacturer: Fairchild Semiconductor

Specifications of FAN5018BMTCX

• Applications: Controller, High-Current, Implementing Low-Voltage CPU Core Power Circuits
• Voltage - Input: 12V
• Number Of Outputs: 1
• Voltage - Output: 0.5 ~ 3.5 V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-TSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

FAN5018B
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
• Coiltronics
• Sumida Electric Company
• Vishay Intertechnology
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 then passing the signal
through a low-pass filter. This summer-filter is the CS
amplifier configured with resistors R
R
set by the following equations, where R
output inductors:
One has the flexibility of choosing either R
It is best to select R
R
Next, use Equation 7 to solve for C
20
C
C
R
R
R
CS
PH(X)
CS
O
PH
PH
CS
[phone]
www.coilcraft.com
[phone]
www.coiltronics.com
[phone]
www.sumida.com
[phone]
www.vishay.com
=
(
(
and C
=
=
X
X
)
)
R
1
R
=
by rearranging Equation 6.
=
6 .
R
PH
L
1
1
CS
R
R
m
×
(
CS
6 .
3 .
L
O
650
X
L
Ω
R
m
m
)
×
(filter). The output resistance of the regulator is
CS
×
Ω
Ω
×
R
nH
100
R
CS
×
L
100
k
CS
O
Ω
k
).
Ω
equal to 100k
=
=
. 4
123
06
nF
k
Ω
CS
Ω
PH(X)
:
, and then solve for
L
is the DCR of the
(summers), and
CS
or R
PH(X)
.
(6)
(7)
It is best to have a dual location for C
dard values can be used in parallel to get as close to the value
desired. For this example, choosing C
good choice. For best accuracy, C
NPO capacitor. A close standard 1% value for R
100k
Inductor DCR Temperature Correction
With the inductor’s DCR being used as the sense element,
and copper wire being the source of the DCR, one needs to
compensate for temperature changes of the inductor’s wind-
ing. Fortunately, copper has a well-known temperature coef-
ficient (TC) of 0.39%/°C.
If R
change in resistance to that of the wire, it will cancel the
temperature variation of the inductor’s DCR. Due to the non-
linear nature of NTC thermistors, resistors R
are needed (see Figure 5) to linearize the NTC and produce
the desired temperature tracking.
The following procedure and expressions will yield values to
use for R
for a given R
1.
2.
3.
To V
sense
CS
OUT
Select an NTC to be used based on type and value. Since
we do not have a value yet, start with a thermistor with a
value close to R
tolerance of better than 5%.
Based on the type of NTC, find its relative resistance
value at two temperatures. The temperatures to use that
work well are 50°C and 90°C. We will call these resis-
tance values A (R
R
1 at 25°C.
Next, find the relative value of R
these temperatures. This is based on the percentage
change needed, which we will initially make 0.39%/°C.
We will call these r
R
Ω
r
r
PH3
and well away from
1
TH(25°C)
2
Switch Node lines
.
Keep this path as
Figure 5. Temperature Compensation Circuit
short as possible
is designed to have an opposite and equal percentage
=
=
To Switch Nodes
CS1
(
(
1
1
R
+
PH2
+
, R
TC
CS
TC
). Note that the NTC’s relative value is always
CS2
R
value.
×
×
PH1
1
1
(
(
T
, and R
T
1
2
CS
−
−
TH(50°C)
R
. The NTC should also have an initial
25
25
1
CS2
and r
)
)
TH
)
)
R
(the thermistor value at 25°C)
R
1.8nF
CS1
)/R
TH
2
C
TC = 0.0039
T
T
where:
CS
1
2
TH(25°C)
CS
= 50°C
= 90°C
PRODUCT SPECIFICATION
inductor or low-side
possible to nearest
Place as close as
should be a 5% or 10%
CS
CS
CS
MOSFET
in the layout so stan-
REV. 1.0.0 Jul/15/05
required for each of
18
17
16
to be 4.7nF is a
) and B (R
CSCOMP
CSSUM
CSREF
CS1
PH(X)
and R
TH(90°C)
CSA
is
CS2
/