ISL6323B Datasheet, PDF (27/35 Pages) Intersil Corporation – Monolithic Dual PWM Hybrid Controller Powering AMD SVI Split-Plane and PVI Uniplane Processors

ISL6323B
6. Calculate the values for R₁ and R₂ for Core.
Equations 35 and 36 will allow for their computation.
K
=
--------------^R----²----^C----^o---^r--^e---------------
R_1Core + R_2Core
(EQ. 35)
------^L---^C-----^o---^r--^e-------
DCR_Core
=
-^R-----¹---^C----^o----^r--^e----^â‹---^R-----²---^C----^o---^r---^e--
R_1Core + R_2Core
⋅
C_Co
re
(EQ. 36)
CASE 2
I_NBM
A
X
⋅
D
C
R_NB
>
I_{--C-----o---r--e---M-----A----X--}
N
⋅
D
C
R_C
o
r
e
(EQ. 37)
In Case 2, the DC voltage across the North Bridge inductor
at full load is greater than the DC voltage across a single
phase of the Core regulator while at full load. Here, the DC
voltage across the North Bridge inductor must be scaled
down to match the DC voltage across the Core inductors,
which will be impressed across the ISEN pins without any
gain. So, the R₂ resistor for the Core inductor RC filters is
left unpopulated and K = 1.
1. Choose a capacitor value for the Core RC filter. A 0.1µF
capacitor is a recommended starting point.
2. Calculate the value for resistor R₁:
R_1Core
=
-----------------^L---^C----^o----^r--^e-----------------
DCR_Core ⋅ C_Core
(EQ. 38)
3. Calculate the value for the R_SET resistor using Equation 39
(Derived from Equation 20).
R_SET
=
4_----0_---0_--
3
⋅
D_-----C_-----R_{-----C----O----R-----E-----}⋅_---K_--
100 μ A
⋅
⎛
⎜
⎝
I_O
C
PC
O
R
E
+
----^V----^I--^N-----–-----^V----^C----^O-----^R----^E-----
2 ⋅ L_CORE ⋅ f_SW
⋅
V_{-----C-V---O-I--N-R-----E--⎠⎟⎞}
Where: K = 1
(EQ. 39)
4. Using Equation 40 (also derived from Equation 20),
calculate the value of K for the North bridge regulator.
K
=
----³-----
400
⋅
R_SET
⋅
----------¹-----------
DCR_NB
⋅
-------------------------------¹---⁰----⁰----^μ----^A---------------------------------
I_OCPNB
+
----^V----^I--^N-----–-----^V----^N----^B-----
2 ⋅ L_NB ⋅ f_SW
⋅
V_{-----N----B--}
V_IN
(EQ. 40)
5. Choose a capacitor value for the North Bridge RC filter. A
0.1µF capacitor is a recommended starting point.
6. Calculate the values for R₁ and R₂ for North Bridge.
Equations 41 and 42 will allow for their computation.
K
=
-----------^R-----²---^N----^B-------------
R_1NB + R_2NB
(EQ. 41)
------^L---^N-----^B-------
DCR_NB
=
-^R-----¹---^N----^B-----^â‹---^R-----²---^N----^B---
R_1NB + R_2NB
⋅
C_N
B
(EQ. 42)
CASE 3
I_NBMAX ⋅ DCR_NB
=
I_{--C-----o---r--e---M-----A----X--}
N
⋅
D
CR_C
o
re
(EQ. 43)
In Case 3, the DC voltage across the North Bridge inductor
at full load is equal to the DC voltage across a single phase
of the Core regulator while at full load. Here, the full scale
DC inductor voltages for both North Bridge and Core will be
impressed across the ISEN pins without any gain. So, the R₂
resistors for the Core and North Bridge inductor RC filters
are left unpopulated and K = 1 for both regulators.
For this Case, it is recommended that the overcurrent trip
point for the North Bridge regulator be equal to the
overcurrent trip point for the Core regulator divided by the
number of core phases.
1. Choose a capacitor value for the North Bridge RC filter. A
0.1µF capacitor is a recommended starting point.
2. Calculate the value for the North Bridge resistor R₁:
R_1NB = _D-----_C-----_R----^L-_N---^N-_B---^B--_â‹---_C----_N-----_B-
(EQ. 44)
3. Choose a capacitor value for the Core RC filter. A 0.1µF
capacitor is a recommended starting point.
5. Calculate the value for the Core resistor R₁:
R_1Core = -_D----_C-----_R-----_C--^L--_o-^C--_r--_eo----^r-_â‹-^e--_C----_C----_o----_r--_e-
(EQ. 45)
6. Calculate the value for the R_SET resistor using Equation 46:
R_SET
=
4_----0_---0_--
3
⋅
-^D----^C-----^R-----^C----^O----^R-----^E-----^â‹---^K--
100 μ A
⋅
⎛
⎝⎜ ^{IO C PC} O R E
+
----^V----^I--^N-----–-----^V----^C----^O-----^R----^E-----
2 ⋅ L_CORE ⋅ f_SW
⋅
V_{-----C-V---O-I--N-R-----E- ⎠⎟⎞}
Where: K = 1
(EQ. 46)
7. Calculate the OCP trip point for the North Bridge regulator
using Equation 47. If the OCP trip point is higher than
desired, then the component values must be recalculated
utilizing Case 1. If the OCP trip point is lower than desired,
then the component values must be recalculated utilized
Case 2.
I_OCPNB
=
100 μ A
⋅
----------¹-----------
DCR_NB
⋅
⎛
⎝
----³-----
400
⋅
R_S
⎞
E T⎠
+
2^----V-⋅^---IL^--N--_N^---–-_B^----V-⋅^---Nf^--_S^--B--_W^---
⋅
-^V----^N----^B--
V_IN
(EQ. 47)
NOTE: The values of R_SET must be greater than 20kΩ and
less than 80kΩ. For all of the 3 cases, if the calculated value
of R_SET is less than 20kΩ, then either the OCP trip point
needs to be increased or the inductor must be changed to an
inductor with higher DCR. If the R_SET resistor is greater than
80kΩ, then a value of R_SET that is less than 80kΩ must be
chosen and a resistor divider across both North Bridge and
Core inductors must be set up with proper gain. This gain
will represent the variable “K” in all equations. It is also very
important that the R_SET resistor be tied between the RSET
pin and the VCC pin of the ISL6323.
27
FN6879.0
March 23, 2009