ISL6334B Datasheet, PDF (26/30 Pages) Intersil Corporation – VR11.1, 4-Phase PWM Controller with Phase Dropping, Droop Disabled and Load Current Monitoring Features

ISL6334B, ISL6334C
to be 1.2x the maximum load current of the specific
application.
With integrated temperature compensation, the sensed
current signal is independent on the operational temperature
of the power stage, i.e. the temperature effect on the current
sense element R_X is cancelled by the integrated
temperature compensation function. R_X in Equation 29
should be the resistance of the current sense element at the
room temperature.
When the integrated temperature compensation function is
disabled by pulling the TCOMP pin to GND, the sensed
current will be dependent on the operational temperature of
the power stage, since the DC resistance of the current
sense element may be changed according to the operational
temperature. R_X in Equation 29 should be the maximum DC
resistance of the current sense element at the all operational
temperature.
In certain circumstances, it may be necessary to adjust the
value of one or more ISEN resistors. When the components
of one or more channels are inhibited from effectively
dissipating their heat so that the affected channels run hotter
than desired, choose new, smaller values of RISEN for the
affected phases (see the section entitled “Channel-Current
Balance” on page 15). Choose R_ISEN,2 in proportion to the
desired decrease in temperature rise in order to cause
proportionally less current to flow in the hotter phase, as
shown in Equation 30:
R_ISEN,2 = R_ISEN ^ΔΔ-----TT----²¹-
(EQ. 30)
In Equation 30, make sure that ΔT₂ is the desired temperature
rise above the ambient temperature, and ΔT₁ is the measured
temperature rise above the ambient temperature. While a
single adjustment according to Equation 30 is usually
sufficient, it may occasionally be necessary to adjust R_ISEN
two or more times to achieve optimal thermal balance
between all channels.
Load-Line Regulation Resistor
The load-line regulation resistor is labelled R_FB in Figure 6.
Its value depends on the desired loadline requirement of the
application.
The desired loadline can be calculated using Equation 31:
R_LL
=
V-----_{D----R----O-----O----P--}
I_FL
(EQ. 31)
where I_FL is the full load current of the specific application,
and VR_DROOP is the desired voltage droop under the full
load condition.
Based on the desired loadline R_LL, the loadline regulation
resistor can be calculated using Equation 32:
R_FB
=
N-----R-----_{I--S----E----N----R----L----L-}
R_X
(EQ. 32)
where N is the active channel number, R_ISEN is the sense
resistor connected to the ISEN+ pin, and R_X is the
resistance of the current sense element, either the DCR of
the inductor or R_SENSE depending on the sensing method.
If one or more of the current sense resistors are adjusted for
thermal balance (as in Equation 30), the load-line regulation
resistor should be selected based on the average value of
the current sensing resistors, as given in Equation 33:
∑ ^R_FB
=
R-----_L---L--
R_X
R_ISEN(n)
n
(EQ. 33)
where R_ISEN(n) is the current sensing resistor connected to
the n^th ISEN+ pin.
Compensation
The two opposing goals of compensating the voltage
regulator are stability and speed. Depending on whether the
regulator employs the optional load-line regulation as
described in Load-Line Regulation, there are two distinct
methods for achieving these goals.
COMPENSATING LOAD-LINE REGULATED
CONVERTER
The load-line regulated converter behaves in a similar
manner to a peak-current mode controller because the two
poles at the output-filter L-C resonant frequency split with
the introduction of current information into the control loop.
The final location of these poles is determined by the system
function, the gain of the current signal, and the value of the
compensation components, R_C and C_C.
Since the system poles and zero are affected by the values
of the components that are meant to compensate them, the
solution to the system equation becomes fairly complicated.
Fortunately there is a simple approximation that comes very
close to an optimal solution. Treating the system as though it
were a voltage-mode regulator by compensating the L-C
poles and the ESR zero of the voltage-mode approximation
yields a solution that is always stable with very close to ideal
transient performance.
C₂ (OPTIONAL)
R_C ^CC
COMP
R_FB
+
V_DROOP
-
FB
VDIFF
FIGURE 17. COMPENSATION CONFIGURATION FOR
LOAD-LINE REGULATED ISL6334B, ISL6334C
CIRCUIT
26
FN6689.2
August 31, 2010