isl6334d Intersil Corporation, isl6334d Datasheet - Page 13

• Manufacturer Part Number: isl6334d
• Description: Vr11.1, 4-phase Pwm Controller With Phase Dropping, Droop Disabled And Load Current Monitoring Features
• Manufacturer: Intersil Corporation

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 ISL6334D should be
utilized. The integrated temperature compensation function is
described in “External Temperature Compensation” on
page 21.
I
I
SEN
SEN
SENSE
FIGURE 5. SENSE RESISTOR IN SERIES WITH INDUCTORS
ISL6334D INTERNAL CIRCUIT
=
=
I
I
L
L
in series with each output inductor can serve as the
C
CURRENT
⋅
⋅
SENSE
I
R
-----------------------
----------------- -
R
is replicated across the sense resistor R
SEN
DCR
R
SENSE
ISEN
ISEN
I
ISEN
n
SEN
=
SEN
I
and C
L
.
R
------------------------- -
, is driven by the value of the sense
R
T
SENSE
ISEN
is needed to match the time delay
T
+
-
(R
ISEN
13
ISEN
ISEN-(n)
ISEN+(n)
and C
L
x C
ISEN
T
to keep the time
T
T
R
) close to 27ns.
(R
I
, or the integrated
SENSE
L
SEN
ISEN
R
C
, is proportional
ISEN(n)
T
C
V
x C
OUT
OUT
T
SENSE
) close to
ISEN
(EQ. 6)
(EQ. 7)
T
to
.
.
ISL6334D
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 ISL6334D to include the combined tolerances of each of
these elements.
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.
The ISL6334D incorporates an internal differential remote
sense amplifier in the feedback path. The amplifier removes
the voltage error encountered when measuring the output
voltage relative to the local controller ground reference point,
FIGURE 6. OUTPUT VOLTAGE REGULATION LOOP
R
FB
V
V
OUT
OUT
EXTERNAL CIRCUIT ISL6334D INTERNAL CIRCUIT
C
R
REF
+
-
C
R
C
REF
C
RGND
COMP
VDIFF
VSEN
n
DAC
REF
FB
from each active channel is summed
AVG
provides a measure of the
COMP
DIFFERENTIAL
REMOTE-SENSE
AMPLIFIER
ERROR AMPLIFIER
+
-
, is compared to
+
-
V
October 29, 2008
COMP
FN6802.0