ADP3208CJCPZ-RL View Datasheet(PDF) - ON Semiconductor
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Description
Manufacturer
ADP3208CJCPZ-RL
ON Semiconductor
ADP3208CJCPZ-RL Datasheet PDF : 41 Pages
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ADP3208C
Figure 36. Temperature-Compensation Circuit Values
The following procedure and expressions yield values for
RCS1, RCS2, and RTH (the thermistor value at 25°C) for a given
RCS value.
1. Select an NTC to be used based on its type and value.
Because the value needed is not yet determined, start with
a thermistor with a value close to RCS and an NTC with an
initial tolerance of better than 5%.
2. Find the relative resistance value of the NTC at two
temperatures. The appropriate temperatures will depend
on the type of NTC, but 50°C and 90°C have been shown
to work well for most types of NTCs. The resistance values
are called A (A is RTH(50°C)/RTH(25°C)) and B (B is
RTH(90°C)/RTH(25°C)). Note that the relative value of the
NTC is always 1 at 25°C.
3. Find the relative value of RCS required for each of the two
temperatures. The relative value of RCS is based on the
percentage of change needed, which is initially assumed to
be 0.39%/°C in this example.
The relative values are called r1 (r1 is 1/(1+ TC × (T1 − 25)))
and r2 (r2 is 1/(1 + TC × (T2 − 25))), where TC is 0.0039,
T1 is 50°C, and T2 is 90°C.
4. Compute the relative values for rCS1, rCS2, and rTH by using
the following equations:
rCS2
=
(A − B) × r1 × r2 − A × (1 − B) × r2 + B × (1 − A) × r1
A × (1 − B) × r1 − B × (1 − A) × r2 − (A − B)
(7)
rCS1 =
(1 − A)
1− A
1 − rCS2 r1 − rCS2
rTH =
1
1 −1
1 − rCS2 rCS1
5. Calculate RTH = rTH × RCS, and then select a thermistor of
the closest value available. In addition, compute a scaling
factor k based on the ratio of the actual thermistor value
used relative to the computed one:
k = RTH (ACTUAL)
(8)
RTH (CALCULATED)
6. Calculate values for RCS1 and RCS2 by using the following
equations:
RCS1 = RCS × k × rCS1
(9)
RCS2 = RCS ×((1 − k) + (k × rCS2 ))
For example, if a thermistor value of 100 kΩ is selected in Step 1,
an available 0603-size thermistor with a value close to RCS is the
Vishay NTHS0603N04 NTC thermistor, which has resistance
values of A = 0.3359 and B = 0.0771. Using the equations in
Step 4, rCS1 is 0.359, rCS2 is 0.729, and rTH is 1.094. Solving for rTH
yields 241 kΩ, so a thermistor of 220 kΩ would be a reasonable
selection, making k equal to 0.913. Finally, RCS1 and RCS2 are found
to be 72.1 kΩ and 166 kΩ. Choosing the closest 1% resistor for
RCS2 yields 165 kΩ. To correct for this approximation, 73.3 kΩ
is used for RCS1.
COUT Selection
The required output decoupling for processors and platforms is
typically recommended by Intel. For systems containing both
bulk and ceramic capacitors, however, the following guidelines
can be a helpful supplement.
Select the number of ceramics and determine the total ceramic
capacitance (CZ). This is based on the number and type of
capacitors used. Keep in mind that the best location to place
ceramic capacitors is inside the socket; however, the physical
limit is twenty 0805-size pieces inside the socket. Additional
ceramic capacitors can be placed along the outer edge of the
socket. A combined ceramic capacitor value of 200 μF to 300 μF
is recommended and is usually composed of multiple 10 μF or
22 μF capacitors.
Ensure that the total amount of bulk capacitance (CX) is within
its limits. The upper limit is dependent on the VID on-the-fly
output voltage stepping (voltage step, VV, in time, tV, with error
of VERR); the lower limit is based on meeting the critical capacitance
for load release at a given maximum load step, ΔIO. The current
version of the IMVP-6+ specification allows a maximum VCORE
overshoot (VOSMAX) of 10 mV more than the VID voltage for a
step-off load current.
⎜⎛
⎟⎞
C X (MIN )
⎜
≥⎜
⎜
⎜
⎝
n
×
⎜⎜⎝⎛
RO
L × ΔIO
+ VOSMAX
ΔI O
⎟⎟⎠⎞ × VVID
−CZ
⎟
⎟
⎟
⎟
⎠
(10)
C X ( MAX )
≤
L
n × k2 × RO2
×
VV
VVID
×
⎜⎛
⎜⎜⎝
1
+
⎜⎜⎝⎛
t
v
VVID
VV
×
n × k × RO
L
⎟⎟⎠⎞2
−1⎟⎟⎟⎠⎞ − CZ
where
k
=
−ln
⎜⎜⎝⎛
VERR
VV
⎟⎟⎠⎞
(11)
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