ISL6316 Datasheet, PDF (11/29 Pages) Intersil Corporation – Enhanced 4-Phase PWM Controller with 6-Bit VID Code Capable of Precision RDS(ON) or DCR Differential Current Sensing for VR10 Application

ISL6316
by the state of PWM3 and PWM4. Tie PWM3 to VCC to
configure for 2-phase operation. Tie PWM4 to VCC to
configure for 3-phase operation.
ISEN1+, ISEN1-; ISEN2+, ISEN2-; ISEN3+, ISEN3-;
ISEN4+, ISEN4- - The ISEN+ and ISEN- pins are current
sense inputs to individual differential amplifiers. The sensed
current is used for channel current balancing, over current
protection, and droop regulation. Inactive channels should
have their respective current sense inputs left open (for
example, open ISEN4+ and ISEN4- for 3-phase operation).
For DCR sensing, connect each ISEN- pin to the node
between the RC sense elements. Tie the ISEN+ pin to the
other end of the sense capacitor through a resistor, R_ISEN.
The voltage across the sense capacitor is proportional to the
inductor current. Therefore, the sense current is proportional
to the inductor current, and scaled by the DCR of the inductor
and R_ISEN.
When configured for R_DS(ON) current sensing, the ISEN1-,
ISEN2-, ISEN3-, and ISEN4- pins are grounded at the lower
MOSFET sources. The ISEN1+, ISEN2+, ISEN3+, and
ISEN4+ pins are then held at a virtual ground. Therefore, a
resistor, connected between these current sense pins and the
drain terminals of the associated lower MOSFET, will carry the
current proportional to the current flowing through that
channel. The sensed current is determined by the negative
voltage across the lower MOSFET when it is ON, which is the
channel current scaled by R_DS(ON) and R_ISEN.
PGOOD - PGOOD indicates that the soft-start is completed
and the output voltage is within the regulated range around
VID setting. It is an open-drain logic output. When OCP or
OVP occurs, PGOOD will be pulled to low. It will also be
pulled low if the output voltage is below the undervoltage
threshold.
OFS - The OFS pin provides a means to program a DC offset
current for generating a DC offset voltage at the REF input.
The offset current is generated via an external resistor and
precision internal voltage references. The polarity of the offset
is selected by connecting the resistor to GND or VCC. For no
offset, the OFS pin should be left unterminated.
TCOMP - Temperature compensation scaling input. The
voltage sensed on the TM pin is utilized as the temperature
input to adjust ldroop and the over current protection limit to
effectively compensate for the temperature coefficient of the
current sense element. To implement the integrated
temperature compensation, a resistor divider circuit is needed
with one resistor being connected from TCOMP to VCC of the
controller and another resistor being connected from TCOMP
to GND. Changing the ratio of the resistor values will set the
gain of the integrated thermal compensation. When integrated
temperature compensation function is not used, connect
TCOMP to GND.
IDROOP - IDROOP is the output pin of sensed average
channel current which is proportional to load current. In the
application which does not require loadline, leave this pin
open. In the application which requires load line, connect this
pin to FB so that the sensed average current will flow through
the resistor between FB and VDIFF to create a voltage drop
which is proportional to load current.
TM - TM is an input pin for VR temperature measurement.
Connect this pin through NTC themistor to GND and a resistor
to Vcc of the controller. The voltage at this pin is reverse
proportional to VR temperature. ISL6316 monitors the VR
temperature based on the voltage at TM pin and outputs
VR_HOT and VR_FAN signals.
VR_HOT - VR_HOT is used as an indication of high VR
temperature. It is an open-drain logic output. It will be open
when the measured VR temperature reaches certain level.
VR_FAN - VR_FAN is an output pin with open-drain logic
output. It will be open when the measured VR temperature
reaches certain level.
Operation
Multiphase Power Conversion
Microprocessor load current profiles have changed to the
point that the advantages of multiphase power conversion are
impossible to ignore. The technical challenges associated
with producing a single-phase converter which is both cost-
effective and thermally viable have forced a change to the
cost-saving approach of multiphase. The ISL6316 controller
helps reduce the complexity of implementation by integrating
vital functions and requiring minimal output components. The
block diagrams on pages 4, 5, 6 and 7 provide top level views
of multiphase power conversion using the ISL6316 controller.
Interleaving
The switching of each channel in a multiphase converter is
timed to be symmetrically out of phase with each of the other
channels. In a 3-phase converter, each channel switches 1/3
cycle after the previous channel and 1/3 cycle before the
following channel. As a result, the three-phase converter has
a combined ripple frequency three times greater than the
ripple frequency of any one phase. In addition, the peak-to-
peak amplitude of the combined inductor currents is reduced
in proportion to the number of phases (Equations 1 and 2).
Increased ripple frequency and lower ripple amplitude mean
that the designer can use less per-channel inductance and
lower total output capacitance for any performance
specification.
Figure 1 illustrates the multiplicative effect on output ripple
frequency. The three channel currents (IL1, IL2, and IL3)
combine to form the AC ripple current and the DC load
current. The ripple component has three times the ripple
frequency of each individual channel current. Each PWM
pulse is terminated 1/3 of a cycle after the PWM pulse of the
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FN9227.0
August 31, 2005