ISL6565A Datasheet, PDF (21/28 Pages) Intersil Corporation – Multi-Phase PWM Controller with Precision rDS(ON) or DCR Current Sensing for VR10.X Application

ISL6565A, ISL6565B
V_IN
ISL6605
PWM(n)
ISL6565B
IL
L
DCR
INDUCTOR
V_L(s)
V_C(s)
R₁
C
R₂
V_OUT
C_OUT
ISEN(n)
ICOMMON
R_ISEN
I_SEN
FIGURE 16. DCR SENSING CONFIGURATION
The time constant of this R-C network must match the time
constant of the inductor L/DCR. Follow the steps below to
choose the component values for this R-C network.
1. Choose an arbitrary value for C. The recommended value
is 0.01µF.
2. Plug the Inductor L and DCR component values, and the
values for C chosen in steps 1, into Equation 28 to
calculate your value for R₁. Do not populate R₂.
R₁
=
----------^L------------
DCR ⋅ C
(EQ. 28)
Due to errors in the inductance or DCR it may be necessary
to adjust the value of R₁ for each phase to match the time
constants correctly.
Once the R-C network components have been chosen, use
Equation 29 to calculate the value of R_ISEN. In Equation 29,
DCR is the DCR of the output inductor at room temperature,
I_FL is the full load operating current, and N is the number of
phases.
R_ISEN = ₇----_0D-----_×^C----₁-^R---₀---^â‹_–---^I₆--^F---_â‹^L---_N--
(EQ. 29)
Adjusting Phase Currents (ISL6565B Only)
Layout issues in the core-power regulator may cause the
currents in each phase to be slightly unbalanced. This
problem can be resolved without any changes to the layout or
any significant cost increase. The solution requires populating
R₂ in certain phases (as shown in Figure 16) to create a
resistor divider ratio, K, for each phase. The time constant of
each new resistor divider R-C sense network must match the
time constant of the old sense network. Follow the steps
below to choose the component values for the resistor
divider R-C network for each phase.
1. Load the regulator to full load and allow the board to heat
until the output voltage stabilizes (usually several
minutes).
2. Measure the current flowing through each phase,
labeling the highest phase current, I_HIGH, and the other,
lower phase currents I_LOW(1) and I_LOW(2).
3. Individually, plug the values for each low phase current,
I_LOW(n), the highest phase current, I_HIGH, the full load
current, I_LOAD, and the number of phases, N, into
Equation 30 to calculate the resistor divider ratio, K_LOW,
for each low phase. (NOTE: The phase with the highest
phase current is the reference phase and it will not use a
resistor divider network, keeping its resistor divider ratio
equal to 1.)
K_LOW(n)
=
1 + -^I-^L----^O----^W------⁽--ⁿ----⁾---–-----^I--^H----^I--^G----^H--
I_LOAD ⁄ N
(EQ. 30)
4. For each phase, calculate the values for the new R-C
network sense resistors, R_1,new and R_2,new, by plugging
in each phase’s new resistor divider ratio, K_LOW, and
each phase’s present sense resistor R₁, into Equations
31 and 32.
R_{1, new}(n)
=
-----^R-----¹---⁽---ⁿ---⁾------
K_LOW(n)
(EQ. 31)
R_{2, new}(n) = -₁----–-----_KR----_L1---_O-⁽--ⁿ--_W--⁾---₍---_n----₎
(EQ. 32)
After calculating the new resistor divider sense resistors, the
phases will be balanced. It may be necessary to adjust the
R_ISEN resistor slightly to correct for any changes in the
desired I_SEN current that results from adding the resistor
dividers.
The phase currents might also have to be adjusted if the
components of one or more phases are inhibited from
effectively dissipating their heat so that the affected phases
run hotter than desired. In this case it may be necessary to
adjust the resistor divider ratio of one or more of the R-C
networks. Doing so adjusts the current through affected
phases and can balance the temperatures of each phase.
Choose R_1,new and R_2,new in relation to the desired change
in temperature, as described in Equations 33 and 34, in order
to cause less current to flow in the hotter phase.
R_1,new = R₁ ^∆∆-----TT----²¹-
(EQ. 33)
R _{2 ,n e w}
=
----------------^R-----¹----^â‹---^R-----²-----------------
R₁
+
R₂
⋅

1

–
∆∆_{----TT----12- }
(EQ. 34)
In Equations 33 and 34, ∆T₂ is the desired temperature rise
above the ambient temperature, and ∆T₁ is the measured
temperature rise above the ambient temperature. It is
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