ISL6556BCBZ Intersil, ISL6556BCBZ Datasheet - Page 12

• Manufacturer Part Number: ISL6556BCBZ
• Description: IC CTRLR MULTIPHASE VRM10 28SOIC
• Manufacturer: Intersil

Specifications of ISL6556BCBZ

• Applications: Controller, Intel VR10X
• Voltage - Input: 3 ~ 12 V
• Number Of Outputs: 4
• Voltage - Output: 0.84 ~ 1.6 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 28-SOIC (7.5mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

pulse width which corrects for any unbalance and drives the
error current toward zero. Figure 4 illustrates Intersil’s
patented current-balance method as implemented on
channel-1 of a multi-phase converter.
Two considerations designers face are MOSFET selection
and inductor design. Both are significantly improved when
channel currents track at any load level. The need for
complex drive schemes for multiple MOSFETs, exotic
magnetic materials, and expensive heat sinks is avoided,
resulting in a cost-effective and easy-to-implement solution
relative to single-phase conversion. Channel-current balance
insures that the thermal advantage of multi-phase
conversion is realized. Heat dissipation in multiple channels
is spread over a greater area than can easily be
accomplished using the single phase approach.
In some circumstances, it may be necessary to deliberately
design some channel-current unbalance into the system. In
a highly compact design, one or two channels may be able to
cool more effectively than the other(s) due to nearby air flow
or heat sinking components. The other channel(s) may have
more difficulty cooling with comparatively less air flow and
heat sinking. The hotter channels may also be located close
to other heat-generating components tending to drive their
temperature even higher. In these cases, the proper
selection of the current sense resistors (R
introduces channel current unbalance into the system.
Increasing the value of R
decreasing it in the hotter channels moves all channels into
thermal balance at the expense of current balance.
Voltage Regulation
The integrating 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 ISL6556B to include the
combined tolerances of each of these elements.
FIGURE 4. CHANNEL-1 PWM FUNCTION AND CURRENT-
V
COMP
NOTE: *Channels 3 and 4 are optional.
BALANCE ADJUSTMENT
+
I
ER
-
+
f(jω)
I
1
-
I
AVG
SAWTOOTH SIGNAL
ISEN
÷
12
N
in the cooler channels and
+
-
Σ
ISEN
in Figure 3)
PWM1
I
I
I
4
3
2
*
*
ISL6556B
The output of the error amplifier, V
sawtooth waveform 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 that controls
voltage regulation is illustrated in Figure 5.
The ISL6556B 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 VID4
through VID12.5. The DAC decodes the 6-bit logic signal
(VID) into one of the discrete voltages shown in Table 1.
Each VID input offers a 20µA 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 leakage
into the driving device is greater than 20µA.
FIGURE 5. OUTPUT VOLTAGE AND LOAD-LINE
R
FB
EXTERNAL CIRCUIT
V
V
OUT
OUT
+
-
V
DROOP
R
-
+
C
REGULATION WITH OFFSET ADJUSTMENT
R
TCOMP
C
C
C
TCOMP
REF
RGND
COMP
VDIFF
VSEN
REF
FB
ISL6556B INTERNAL CIRCUIT
COMP
1k
VID DAC
I
AVG
ERROR AMPLIFIER
DIFFERENTIAL
REMOTE-SENSE
AMPLIFIER
, is compared to the
+
-
+
-
December 28, 2004
V
COMP
DIFF
FN9097.4
, is