ADP3168JRUZ-REEL AD [Analog Devices], ADP3168JRUZ-REEL Datasheet - Page 16

• Manufacturer Part Number: ADP3168JRUZ-REEL
• Description: 6-Bit, Programmable 2-, 3-, 4-Phase Synchronous Buck Controller
• Manufacturer: AD [Analog Devices]

ADP3168
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 com-
pensate for temperature changes of the inductor’s winding.
Fortunately, copper has a well-known temperature coefficient
(TC) of 0.39%/°C.
If R
change in resistance to that of the wire, it cancels the temper-
ature variation of the inductor’s DCR. Due to the nonlinear
nature of NTC thermistors, resistors R
(see Figure 12) to linearize the NTC and produce the desired
temperature tracking.
The following procedure and expressions yield values to use for
R
value.
1.
2.
3.
CS1
CS
, R
Select an NTC based on type and value. Because there is no
value yet, start with a thermistor with a value close to R
The NTC should also have an initial tolerance of better
than 5%.
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. We will call these resistance values
A (R
the NTC’s relative value is always 1 at 25°C.
Find the relative value of R
temperatures. This is based on the percentage change
needed, which in this example is initially 0.39%/°C.
These are called r
(1/(1 + TC × (T
and T
ADP3168
is designed to have an opposite and equal percentage
CS2
PLACE AS CLOSE AS POSSIBLE
CSCOMP
, and R
TH(50°C
CSSUM
TO NEAREST INDUCTOR
CSREF
Figure 12. Temperature Compensation Circuit Values
OR LOW-SIDE MOSFET
2
= 90°C.
)/R
TH
18
17
16
TH(25°C)
(the thermistor value at 25°C) for a given R
2
− 25))), where TC = 0.0039, T
1.8nF
1
C
(1/(1 + TC × (T
CS
) and B (R
R
R
CS1
TH
CS
required for each of these
R
TH(90°C
CS2
CS1
1
)/R
R
AS SHORT AS POSSIBLE
− 25))) and r
AND WELL AWAY FROM
and R
PH1
SWITCH NODE LINES
TH(25°C)
SWITCH
KEEP THIS PATH
NODES
TO
CS2
R
PH2
). Note that
are needed
1
= 50°C,
2
R
PH3
SENSE
V
TO
OUT
CS
Rev. B | Page 16 of 24
.
CS
4.
5.
6.
For this example, R
with a thermistor value of 100 kΩ. Looking through available
0603 size thermistors, we find a Vishay NTHS0603N01N1003JR
NTC thermistor with A = 0.3602 and B = 0.09174. From these
we compute R
Solving for R
k = 0.9302. Finally, we find R
73.9 kΩ. Choosing the closest 1% resistor values yields a choice
of 35.7 kΩ and 73.2 kΩ.
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
and flowing through R
Equation 11:
The closest standard 1% resistor value is 1.33 kΩ.
Compute the relative values for R
Calculate R
thermistor available. Also compute a scaling factor k based
on the ratio of the actual thermistor value used relative to
the computed one:
Finally, calculate values for R
R
k =
R
R
R
R
R
R
CS
CS
TH
CS1
CS2
B
B
2
1
R
=
=
=
=
=
TH
=
=
R
V
1
1
(
TH
1
VID
5 .
(
R
A
R
CALCULATED
−
TH
−
CS
CS
CS1
(
−
V
R
1
ACTUAL
I
−
1
yields 107.51 kΩ, so we choose 100 kΩ, making
15
CS
R
FB
B
TH
A
×
×
−
= 0.3796, R
CS2
V
)
(
2
1
×
×
. 1
k
(
ONL
µA
= R
−
CS
−
1
(
1
(
γ
×
480
1
−
1
A
)
γ
−
has been chosen to be 100 kΩ , so we start
−
1
γ
×
TH
)
B
)
R
k
−
B
CS
. The value of R
γ
A
1
CS1
) (
V
2
)
R
× R
1
×
+
×
CS
=
γ
−
2
CS2
1
CS
k
CS1
. 1
A
−
, then select the closest value of
×
33
= 0.7195, and R
×
B
and R
γ
(
×
1
CS1
CS
k
(
−
1
Ω
2
and R
B
−
)
CS2
)
CS1
)
A
×
B
)
, R
can be found using
γ
to be 35.3 kΩ and
×
2
CS2
γ
CS2
+
2
B
−
using Equation 10:
, and R
×
(
TH
A
(11)
(
1
−
= 1.0751.
−
B
A
)
TH
)
×
using:
γ
1
(8)
(9)
(10)
FB
)