isl6228 Intersil Corporation, isl6228 Datasheet - Page 7

• Manufacturer Part Number: isl6228
• Description: High-performance Dual-output Buck Controller For Notebook Applications
• Manufacturer: Intersil Corporation

parallel with the trace connecting the LGATE1 pin to the gate
of the Channel 1 converter low-side MOSFET.
PGND2 (Pin 18)
The PGND2 pin is the current return path for the Channel 2
converter low-side MOSFET gate driver. Connect the
PGND2 pin to the source of the Channel 2 converter low-
side MOSFET through a low impedance path, preferably in
parallel with the trace connecting the LGATE2 pin to the gate
of the Channel 2 converter low-side MOSFET.
LGATE2 (Pin 19)
The LGATE2 pin is the output of the Channel 2 converter
low-side MOSFET gate driver. Connect to the gate of the
Channel 2 converter low-side MOSFET.
PVCC2 (Pin 20)
The PVCC2 pin is the input voltage bias for the Channel 2
low-side MOSFET gate drivers. Connect +5V to the PVCC2
pin. Decouple with at least 1µF of an MLCC capacitor across
the PVCC2 and PGND2 pin.
BOOT2 (Pin 21)
The BOOT2 pin stores the input voltage for the Channel 2
high-side MOSFET gate driver. Connect an MLCC capacitor
across the BOOT2 and PHASE2 pins. The boot capacitor is
charged through an internal boot diode connected from the
PVCC2 pin to the BOOT2 pin, each time the PHASE2 pin
drops below PVCC2 minus the voltage dropped across the
internal boot diode.
UGATE2 (Pin 22)
The UGATE2 pin is the output of the Channel 2 high-side
MOSFET gate driver. Connect to the gate of the Channel 2
converter high-side MOSFET.
PHASE2 (Pin 23)
The PHASE2 pin is the current return path for the Channel 2
high-side MOSFET gate driver. Connect the PHASE2 pin to
the node consisting of the high-side MOSFET source, the
low-side MOSFET drain, and the output inductor of the
Channel 2 converter.
EN2 (Pin 24)
The EN2 pin is the on/off switch of Channel 2. The soft-start
sequence begins when the EN2 pin is pulled above the
rising threshold voltage V
power-on reset (POR) rising threshold voltage
When the EN2 pin is pulled below the falling threshold
voltage V
OCSET2 (Pin 25)
The OCSET2 pin measures the Channel 2 inductor current
and programs the threshold of the OCP overcurrent fault
protection.
ENTHF
, PWM2 immediately stops.
ENTHR
7
and VCC2 is above the
V VCC_THR
.
ISL6228
VO2 (Pin 26)
The VO2 pin measures the Channel 2 converter output
voltage and is used as an input to the Channel 2 R
modulator. It also serves as part of Channel 2 inductor
current sensing and the OCP overcurrent fault protection
circuit.
FB2 (Pin 27)
The FB2 pin is the inverting input of the control-loop error
amplifier for Channel 2. The Channel 2 converter output
voltage regulates to 600mV from the FB2 pin to the GND pin.
Program the desired output voltage with a resistor network
connected across the VO2, FB2, and GND pins. Select the
resistor values such that FB2 to GND is 600mV when the
converter output voltage is at the programmed regulation
value.
PGOOD2 (Pin 28)
The PGOOD2 pin is an open-drain output that indicates
when the Channel 2 converter is able to supply regulated
voltage. Connect the PGOOD2 pin to +5V through a pull-up
resistor.
Theory of Operation
Two Separate Channels
The ISL6228 is a dual channel controller. Pins 4~17 are
dedicated to Channel 1, and pins 1~3 and pins 18~28 are
dedicated to Channel 2. The two channels are identical and
almost entirely independent, with the exception of sharing
the GND pin. Unless otherwise stated, only an individual
channel is discussed, and the conclusion applies to both
channels.
Modulator
The ISL6228 modulator features Intersil’s R
hybrid of fixed frequency PWM control and variable
frequency hysteretic control. Intersil’s R
simultaneously affect the PWM switching frequency and
PWM duty cycle in response to input voltage and output load
transients. The R
which is an analog representation of the output inductor
ripple current. The duty-cycle of V
and discharge current through a ripple capacitor C
current through C
amplifier g
The positive slope of V
V
The negative slope of V
Where g
V
RPOS
RNEG
=
=
m
(
g
m
g
is the gain of the transconductance amplifier.
m
m
that measures the VIN and VO pin voltages.
⋅
)
V
⋅
(
OUT
V
3
R
IN
modulator synthesizes an AC signal V
is provided by a transconductance
–
V
R
OUT
R
can be written as Equation 1:
can be written as Equation 2:
)
R
is the result of charge
3
technology can
3
technology, a
August 27, 2007
R
3
. The
PWM
FN9095.1
(EQ. 2)
(EQ. 1)
R
,