ISL6334 INTERSIL [Intersil Corporation], ISL6334 Datasheet - Page 15

• Manufacturer Part Number: ISL6334
• Description: VR11.1, 4-Phase PWM Controller with Light Load Efficiency Enhancement and Load Current Monitoring
• Manufacturer: INTERSIL [Intersil Corporation]

The voltage on the capacitor V
proportional to the channel current I
If the R-C network components are selected such that the
RC time constant (= R*C) matches the inductor time
constant (= L/DCR), the voltage across the capacitor V
equal to the voltage drop across the DCR, i.e., proportional
to the channel current.
With the internal low-offset current amplifier, the capacitor
voltage V
Therefore, the current out of ISEN+ pin, I
to the inductor current.
Because of the internal filter at ISEN- pin, one capacitor, C
is needed to match the time delay between the ISEN- and
ISEN+ signals. Select the proper C
constant of R
Equation 6 shows that the ratio of the channel current to the
sensed current, I
resistor and the DCR of the inductor.
RESISTIVE SENSING
For accurate current sense, a dedicated current-sense resistor
R
current sense element (see Figure 5). This technique is more
accurate, but reduces overall converter efficiency due to the
additional power loss on the current sense element R
The same capacitor C
between ISEN- and ISEN+ signals. Select the proper C
keep the time constant of R
27ns.
Equation 7 shows the ratio of the channel current to the
sensed current I
The inductor DCR value will increase as the temperature
increases. Therefore, the sensed current will increase as the
temperature of the current sense element increases. In order
to compensate the temperature effect on the sensed current
signal, a Positive Temperature Coefficient (PTC) resistor can
be selected for the sense resistor R
temperature compensation function of ISL6334, ISL6334A
should be utilized. The integrated temperature compensation
function is described in “External Temperature Compensation”
on page 24.
V
I
I
SEN
SEN
SENSE
C
s ( )
=
=
=
I
I
L
L
in series with each output inductor can serve as the
⎛
⎝
-------------------------------------------------------------------- -
C
s
⋅
⋅
R
-----------------------
⋅
----------------- -
R
is replicated across the sense resistor R
DCR
R
-------------
DCR
SENSE
ISEN
ISEN
ISEN
L
(
SEN
s RC
SEN
+
⋅
and C
1
⎞
⎠
.
, is driven by the value of the sense
T
⋅
+
(
is needed to match the time delay
DCR I
1
T
)
(R
ISEN
15
⋅
ISEN
L
C
and C
)
, can be shown to be
x C
ISEN
T
L
. See Equation 5.
to keep the time
T
T
) close to 27ns.
(R
, or the integrated
SEN
ISEN
, is proportional
x C
T
SENSE
) close to
ISL6334, ISL6334A
ISEN
(EQ. 5)
(EQ. 6)
(EQ. 7)
T
C
to
.
is
.
T
,
Channel-Current Balance
The sensed current I
together and divided by the number of active channels. The
resulting average current I
total load current. Channel current balance is achieved by
comparing the sensed current of each channel to the
average current to make an appropriate adjustment to the
PWM duty cycle of each channel with Intersil’s patented
current-balance method.
Channel current balance is essential in achieving the
thermal advantage of multiphase operation. With good
current balance, the power loss is equally dissipated over
multiple devices and a greater area.
Voltage Regulation
The compensation network shown in Figure 6 assures that
the steady-state error in the output voltage is limited only to
the error in the reference voltage (output of the DAC) and
offset errors in the OFS current source, remote-sense and
error amplifiers. Intersil specifies the guaranteed tolerance of
the ISL6334, ISL6334A to include the combined tolerances
of each of these elements.
The sensed average current I
This current will develop voltage drop across the resistor
between FB and VDIFF pins for droop control. ISL6334,
ISL6334A can not be used for non-droop applications.
The output of the error amplifier, V
sawtooth waveforms to generate the PWM signals. The
PWM signals control the timing of the Intersil MOSFET
drivers and regulate the converter output to the specified
reference voltage. The internal and external circuitry, which
control voltage regulation, are illustrated in Figure 6.
ISL6334, ISL6334A INTERNAL CIRCUIT
FIGURE 5. SENSE RESISTOR IN SERIES WITH INDUCTORS
CURRENT
SENSE
I
SEN
I
n
=
I
L
R
------------------------- -
n
R
SENSE
ISEN
from each active channel is summed
+
-
AVG
AVG
provides a measure of the
ISEN-(n)
ISEN+(n)
L
is tied to FB internally.
COMP
R
I
SENSE
, is compared to
L
R
C
ISEN(n)
T
C
V
February 26, 2008
OUT
OUT
FN6482.0