ADP3193AJCPZ-RL View Datasheet(PDF) - Analog Devices
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ADP3193AJCPZ-RL Datasheet PDF : 32 Pages
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INDUCTOR DCR TEMPERATURE CORRECTION
When the inductor DCR is used as the sense element and
copper wire is used as the source of the DCR, the user needs to
compensate for temperature changes of the inductor’s winding.
Fortunately, copper has a well-known temperature coefficient (TC)
of 0.39%/°C.
If RCS is designed to have an opposite and equal percentage of
change in resistance to that of the wire, it cancels the tempera-
ture variation of the inductor DCR. Due to the nonlinear nature of
negative temperature coefficient (NTC) thermistors, Resistors RCS1
and RCS2 are needed. See Figure 11 to linearize the NTC and
produce the desired temperature tracking.
PLACE AS CLOSE AS POSSIBLE
TO NEAREST INDUCTOR
OR LOW-SIDE MOSFET
RTH
TO
SWITCH
NODES
TO
VOUT
SENSE
ADP3193A
CSCOMP
13
CCS1
CSSUM
12
CSREF
11
RPH1
RPH2
RPH3
RCS1
RCS2
CCS2
KEEP THIS PATH
AS SHORT AS POSSIBLE
AND WELL AWAY FROM
SWITCH NODE LINES
Figure 11. Temperature-Compensation Circuit Values
The following procedure and equations yield values to use for
RCS1, RCS2, and RTH (the thermistor value at 25°C) for a given
RCS value.
1. Select an NTC based on type and value. Because the value
is unknown, use a thermistor with a value close to RCS. The
NTC should also have an initial tolerance of better than 5%.
2. Based on the type of NTC, find its relative resistance
value at two temperatures. The temperatures that work
well are 50°C and 90°C. These resistance values are called
A (RTH(50°C))/RTH(25°C)) and B (RTH(90°C))/RTH(25°C)). The relative
value of the NTC is always 1 at 25°C.
3. Find the relative value of RCS required for each of these
temperatures. This is based on the percentage of change
needed, which in this example is initially 0.39%/°C. These
temperatures are called r1 (1/(1 + TC × (T1 − 25°C)))
and r2 (1/(1 + TC × (T2 − 25°C))), where TC = 0.0039 for
copper, T1 = 50°C, and T2 = 90°C. From this, r1 = 0.9112 and
r2 = 0.7978.
ADP3193A
4. Compute the relative values for RCS1, RCS2, and RTH using
rCS2
=
(A
− B) × r1 × r2 − A × (1 − B) × r2 + B × (1 − A) ×
A × (1 − B) × r1 − B × (1 − A) × r2 − (A − B)
r1
(8)
rCS1 =
(1− A)
1−A
(9)
1 − rCS2 r1 − rCS2
rTH =
1
1 −1
(10)
1 − rCS2 rCS1
Calculate RTH = rTH × RCS, and then select the closest value
thermistor 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)
RTH (CALCULATED)
(11)
5. Calculate values for RCS1 and RCS2 using Equation 12 and
Equation 13.
RCS1 = RCS × k × rCS1
(12)
( ( )) RCS2 = RCS × (1− k) + k × rCS2
(13)
In this example, RCS is calculated to be 114 kΩ. Look for an
available 100 kΩ, 0603-size thermistor. One such thermistor
is the Vishay NTHS0603N01N1003JR NTC thermistor with
A = 0.3602 and B = 0.09174. From these values, rCS1 = 0.3795,
rCS2 = 0.7195, and rTH = 1.075.
Solving for RTH yields 122.55 kΩ; therefore, 100 kΩ is chosen,
making k = 0.816. Next, find RCS1 and RCS2 to be 35.3 kΩ and
87.9 kΩ. Finally, choose the closest 1% resistor values, which
yields a choice of 35.7 kΩ and 88.7 kΩ.
OUTPUT OFFSET
The Intel specification requires that with no load the nominal
output voltage of the regulator be offset to a value lower than the
nominal voltage corresponding to the VID code. The offset is
set by a constant current source flowing out of the FB pin (IFB)
and flowing through RB.B The value of RBB can be found using
Equation 14.
RB
= VVID −VONL
I FB
(14)
1.4 V− 1.381 V
RB =
15 μA
= 1.27 kΩ
The closest standard 1% resistor value is 1.27 kΩ.
Rev. 0 | Page 21 of 32
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