FAN53168MTC FAIRCHILD [Fairchild Semiconductor], FAN53168MTC Datasheet - Page 19

• Manufacturer Part Number: FAN53168MTC
• Description: 6-Bit VID Controlled 2-4 Phase DC-DC Controller
• Manufacturer: FAIRCHILD [Fairchild Semiconductor]

PRODUCT SPECIFICATION
5. Calculate R
6. Finally, calculate values for R
Output Offset
Intel’s specification requires that at no load the nominal
output voltage of the regulator be offset to a lower value than
the nominal voltage corresponding to the VID code. The
offset is set by a constant current source flowing out of the
FB pin (I
found using Equation 11:
C
The required output decoupling for the regulator is typically
recommended by Intel for various processors and platforms.
One can also use some simple design guidelines to determine
what is required. These guidelines are based on having both
bulk and ceramic capacitors in the system.
The first thing is to select the total amount of ceramic capac-
itance. This is based on the number and type of capacitor to
be used. The best location for ceramics is inside the socket,
with 12 to 18 of size 1206 being the physical limit. Others
can be placed along the outer edge of the socket as well.
REV. 1.0.0 6/9/03
R
R
B
OUT
B
=
=
R
of thermistor available. Also compute a scaling factor k
based on the ratio of the actual thermistor value used
relative to the computed one:
following:
k
R
Ω.
CS2
CS1
V
-------------------------------- -
1.5V 1.480V
------------------------------------- -
Selection
=
VID
FB
------------------------------------------------ -
R
=
TH CALCULATED
15µA
=
I
) and flowing through R
R
–
FB
–
R
V
TH ACTUAL
(
R
CS
ONL
CS
Ω
TH
(
×
×
= r
(
k
(
Ω
1 k
×
TH
=
–
r
CS1
1.33kΩ
)
x R
)
)
+
CS
(
k
, then select the closest value
×
µ
Ω
r
CS1
CS2
B
. The value of R
Ω
and R
)
)
CS2
Ω.
using the
Ω
Ω
B
can be
Ω
K
where
To meet the conditions of these expressions and transient
response, the ESR of the bulk capacitor bank (R
less than two times the droop resistance, R
is larger than C
the-fly specification and may require the use of a smaller
inductor or more phases (and may have to increase the
switching frequency to keep the output ripple the same).
For our example, 22 10µF 1206 MLC capacitors
(C
is 250mV in 150µs with a setting error of 2.5mV. Solving
for the bulk capacitance yields:


where K = 4.6
frequency transient spike. This can be tested using:
L
In this example, L
tors, which satisfies this limitation. If the L
bulk capacitor bank is too large, the number of MLC
C
C
C
C
L
X
X
X MAX
X MAX
X MIN
X MIN
1
=
Z
(
(
(
≤
(
+
≤
= 220µF) were used. The VID on-the-fly step change


1n
220µF
C
150µs 1.5V
------------------------------------------------------------------------------------ -
Z
)
)


)
)
≥
×
≥
V
----------------- -
≤
≤
∆
VERR
R




------------------ -
nK
V
----------------------------------------------------------------------- - ×
3 4.6
---------------------------------------------- - 200µF
3 1.3mΩ
------------------------------------ C
n R
O
×
V
×
2
×
250mV 650nH
×
×
2
L
650nH 60A
(
R
L ∆I
1.3mΩ
X(MAX)


650nH 250mV
O
×
O
2
2
X
×
×
×
×
----------- -
V
is 375pH for the eight A1-Poly capaci-
V
O
V
(
×
×
3
VID
1.3mΩ
)
VID
V
, the system will not meet the VID on-
×
2
×
×
1.5V
4.6
=
×
–



372pH
×
)
Z
1
–
2


1.3mΩ
+
×


1.5V
t
V
V
----------- -
V


VID


V
2
1 –
=
 220µF

×
–
O
6.45mF
nKR
--------------- -
X
. If the C
Ω
of the chosen
L
O
X


) should be
2
=
FAN53168
–
23.9mF
1
X(MIN)



Ω
–
C
19
Z