ISL6327 Intersil Corporation, ISL6327 Datasheet - Page 13

• Manufacturer Part Number: ISL6327
• Description: Enhanced 6-Phase PWM Controller
• Manufacturer: Intersil Corporation

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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
serve as the current sense element (see Figure 4). 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
to 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 ISL6327 should be
utilized. The integrated temperature compensation function
is described in the Temperature Compensation section.
Channel-Current Balance
The sensed current I
together and divided by the number of active channels. The
resulting average current I
I
I
SEN
SEN
FIGURE 4. SENSE RESISTOR IN SERIES WITH INDUCTORS
=
=
ISL6327 INTERNAL CIRCUIT
I
I
L
L
CURRENT
SENSE
⋅
⋅
SENSE
I
----------------- -
R
R
-----------------------
SEN
DCR
R
ISEN
SENSE
I
n
ISEN
=
SEN
SEN
SENSE
in series with each output inductor can
I
L
R
------------------------- -
.
n
is driven by the value of the sense
R
SENSE
T
from each active channel are summed
ISEN
.
is needed to match the time delay
+
-
AVG
ISEN
13
provides a measure of the
ISEN-(n)
ISEN+(n)
L
and C
ISEN
T
R
I
SENSE
, or the integrated
L
(R
ISEN
R
C
ISEN(n)
T
C
V
OUT
OUT
x C
T
) close
(EQ. 6)
(EQ. 7)
T
to
ISL6327
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 5 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 ISL6327 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 circuitries which
control the voltage regulation are illustrated in Figure 5.
The ISL6327 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
resulting in a more accurate means of sensing output
voltage. Connect the microprocessor sense pins to the non-
inverting input, VSEN, and inverting input, RGND, of the
remote-sense amplifier. The remote-sense output, V
connected to the inverting input of the error amplifier through
an external resistor.
A digital-to-analog converter (DAC) generates a reference
voltage based on the state of logic signals at pins VID7
through VID0. The DAC decodes the 8-bit logic signal (VID)
into one of the discrete voltages shown in Table 1. Each VID
input offers a 45µA pull-up to an internal 2.5V source for use
with open-drain outputs. The pull-up current diminishes to
zero above the logic threshold to protect voltage-sensitive
output devices. External pull-up resistors can augment the
pull-up current sources in case the leakage into the driving
device is greater than 45µA.
COMP
, is compared to the
June 5, 2006
DIFF
FN9276.1
, is