ISL6556BCR-T Intersil, ISL6556BCR-T Datasheet - Page 15

• Manufacturer Part Number: ISL6556BCR-T
• Description: IC CTRLR MULTIPHASE VRM10 32-QFN
• Manufacturer: Intersil

Specifications of ISL6556BCR-T

• 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: 32-VQFN Exposed Pad, 32-HVQFN, 32-SQFN, 32-DHVQFN
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

on-the-fly VID changes in a controlled manner. Supervising
the safe output voltage transition within the DAC range of the
processor without discontinuity or disruption is a necessary
function of the core-voltage regulator.
The ISL6556B checks the VID inputs six times every
switching cycle. If the VID code is found to have changed,
the controller waits half of a complete cycle before executing
a 12.5mV change. If during the half-cycle wait period, the
difference between DAC level and the new VID code
changes sign, no change is made. If the VID code is more
than 1 bit higher or lower than the DAC (not recommended),
the controller will execute 12.5mV changes six times per
cycle until VID and DAC are equal. It is for this reason that it
is important to carefully control the rate of VID stepping in 1-
bit increments.
In order to ensure the smooth transition of output voltage
during VID change, a VID step change smoothing network is
required for an ISL6556B based voltage regulator. This
network is composed by a 1kΩ internal resistor between the
output of DAC and the C
The selection of C
VID change and the allowable delay time.
Assuming the microprocessor controls the VID change at 1
bit every T
given by Equation 9.
As an example, for a VID step change rate of 5µs per bit, the
value of C
Temperature Compensation
The MOSFET r
temperature. This means that a circuit using r
sense channel current is subject to a corresponding error in
current measurement. In order to compensate for this
temperature-related error, a temperature compensation
circuit is provided within ISL6561. This circuit senses the
internal IC temperature and, based on a resistor-selectable
scaling factor, adjust the droop current flow to the FB pin.
When the TCOMP resistor is properly selected, the droop
current can accurately represent the load current to achieve
a linear, temperature-independant load line.
The value of the Tcomp resistor can be determined using
Equation 10.
In Equation 10, K
between the ISL6561 and the lower MOSFET. It represents
how closely the controller temperature tracks the lower
MOSFET temperature. The value of K
75% and 100%. K
transconductance of internal compensation circuit. Its value
C
R
REF
TCOMP
=
0.004X T
=
REF
VID
--------------------- -
K
, the relationship between C
T
is 22nF based on Equation 9.
α
DS(ON)
K
TC
VID
T
REF
TC
is the temperature coupling coefficient
is the temperature dependant
is based on the time duration for 1 bit
varies in proportion to varying
REF
15
between REF pin to ground.
T
is typically between
REF
DS(ON)
and T
VID
(EQ. 10)
to
(EQ. 9)
is
ISL6556B
is designed as 1µA/V/°C. The temperature coefficient of
MOSFET r
change in resistance and the change in temperature.
Resistance is normalized to the value at 25°C and the value
of
According to Equation 10, a voltage regulator with 80%
thermal coupling coefficient between the controller and lower
MOSFET and 0.4%/°C temperature coefficient of MOSFET
r
Initialization
Prior to initialization, proper conditions must exist on the
enable inputs and VCC. When the conditions are met, the
controller begins soft-start. Once the output voltage is within
the proper window of operation, PGOOD asserts logic.
Enable and Disable
While in shutdown mode, the PWM outputs are held in a
high-impedance state to assure the drivers remain off. The
following input conditions must be met before the ISL6556B
is released from shutdown mode.
DS(ON)
1. The bias voltage applied at VCC must reach the internal
2. The ISL6556B features an enable input (EN) for power
α
FIGURE 8. POWER SEQUENCING USING THRESHOLD-
power-on reset (POR) rising threshold. Once this
threshold is reached, proper operation of all aspects of
the ISL6556B is guaranteed. Hysteresis between the
rising and falling thresholds assure that once enabled,
the ISL6556B will not inadvertently turn off unless the
bias voltage drops substantially (see Electrical
Specifications).
sequencing between the controller bias voltage and
another voltage rail. The enable comparator holds the
ISL6556B in shutdown until the voltage at EN rises above
1.24V. The enable comparator has about 100mV of
hysteresis to prevent bounce. It is important that the
is typically between 0.35%/°C and 0.50%/°C.
CIRCUIT
FAULT LOGIC
SOFT-START
requires a 5kΩ TCOMP resistor.
POR
ISL6556B INTERNAL CIRCUIT
DS(ON)
AND
SENSITIVE ENABLE (EN) FUNCTION
is given by
ENABLE
COMPARATOR
+
-
α
1.24V
. This is the ratio of the
VCC
EN
ENLL
(ISL6556BCR ONLY)
EXTERNAL CIRCUIT
10.7kΩ
1.40kΩ
December 28, 2004
+12V
FN9097.4