ISL6323A Datasheet, PDF (28/35 Pages) Intersil Corporation – Monolithic Dual PWM Hybrid Controller Powering AMD SVI Split-Plane and PVI Uniplane Processors

ISL6323A
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
r
e
(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
=
--------------^L----^N----^B---------------
DCR_NB ⋅ C_NB
(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
=
-----------------^L---^C----^o----^r--^e-----------------
DCR_Core ⋅ C_Core
(EQ. 45)
6. Calculate the value for the R_SET resistor using Equation 46:
R_SET
=
4_----0_---0_--
3
⋅
-^D----^C-----^R-₁---₀-^C--₀--^O--_μ--^R--_A---^E-----^â‹---^K--
⋅
⎛
⎝⎜ ^{IO C PC} O R E
+
2^----V-⋅^---IL^--N--_C^---–-_O^----V-_R^---C-_E^---O--⋅^---Rf^--_S^--E--_W^---
⋅
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
⋅
⎝⎛ ₄^----₀₃^---₀^--
⋅
R_S
⎞
E T⎠
+
----^V----^I--^N-----–-----^V----^N----^B-----
2 ⋅ L_NB ⋅ f_SW
⋅
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.
Inductor DCR Current Sensing Component Fine
Tuning
MOSFET
DRIVER
V_IN
UGATE(n)
LGATE(n)
IL_n
L
DCR
INDUCTOR
V_L(s)
V_C(s)
R₁
C
V_OUT
C_OUT
ISL6323A INTERNAL CIRCUIT
R₂
I_n
K_I
KI
=
-⁴----⁰---^k----^Ω----
RSET
SAMPLE
+
-
I_SEN
V_C(s)
R_ISEN
2.4kΩ
ISENn-
ISENn+
RSET
R_SET
VCC
FIGURE 20. DCR SENSING CONFIGURATION
Due to errors in the inductance and/or DCR it may be
necessary to adjust the value of R₁ and R₂ to match the time
constants correctly. The effects of time constant mismatch
can be seen in the form of droop overshoot or undershoot
during the initial load transient spike, as shown in Figure 21.
Follow the steps below to ensure the R-C and inductor
L/DCR time constants are matched accurately.
1. If the regulator is not utilizing droop, modify the circuit by
placing the frequency set resistor between FS and
Ground for the duration of this procedure.
28
FN6878.0