ISL6228EVAL3Z Intersil, ISL6228EVAL3Z Datasheet - Page 8

• Manufacturer Part Number: ISL6228EVAL3Z
• Description: EVALUATION BOARD FOR ISL6228
• Manufacturer: Intersil
• Series: Robust Ripple Regulator™ (R³)r

Specifications of ISL6228EVAL3Z

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 2, Non-Isolated
• Voltage - Output: 1.5V or 1.8V, 1.8V
• Current - Output: 8A, 8A
• Voltage - Input: 3.3 ~ 25V
• Regulator Topology: Buck
• Frequency - Switching: 270kHz, 300kHz
• Board Type: Fully Populated
• Utilized Ic / Part: ISL6228
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

current through C
amplifier g
The positive slope of V
The negative slope of V
Where g
A window voltage V
amplifier output voltage V
which the ripple voltage V
V
pins. The V
comparator in which V
and V
PWM pulses being generated as V
V
proportional to the slew rates of the positive and negative
slopes of V
between V
Power-On Reset
The ISL6228 is disabled until the voltage at the VCC pin has
increased above the rising power-on reset (POR) V
threshold voltage. The controller will be disabled when the
voltage at the VCC pin decreases below the falling POR
V
EN, Soft-Start and PGOOD
The ISL6228 uses a digital soft-start circuit to ramp the
output voltage of the converter to the programmed regulation
setpoint at a predictable slew rate. The slew rate of the
soft-start sequence has been selected to limit the in-rush
current through the output capacitors as they charge to the
desired regulation voltage. When the EN pin is pulled above
the rising EN threshold voltage V
V
V
RPOS
W
COMP
CCF
RNEG
Ripple Capacitor Voltage C R
FIGURE 2. MODULATOR WAVEFORMS DURING LOAD
is set by a resistor connected across the FSET and GND
W
threshold voltage.
=
=
thresholds. The PWM switching frequency is
is the higher threshold voltage. Figure 2 shows
m
(
m
g
W
g
is the gain of the transconductance amplifier.
R;
R,
m
m
that measures the VIN and VO pin voltages.
and V
⋅
)
TRANSIENT
it is inversely proportional to the voltage
V
V
⋅
COMP,
(
OUT
V
R
IN
COMP.
is provided by a transconductance
W
–
⁄
C
V
is referenced with respect to the error
COMP
and V
R
R
OUT
R
can be written as Equation 1:
COMP
R
can be written as Equation 2:
) C
is compared. The amplitude of
W
⁄
is the lower threshold voltage
8
R
Error Amplifier Voltage V COMP
signals feed into a window
, creating an envelope into
ENTHR
R
Window Voltage V W
traverses the V
, the PGOOD
PWM
CCR
W
(EQ. 2)
(EQ. 1)
and
ISL6228
Soft-Start Delay t
rise. The FB pin ramps to 0.6V in approximately 1.5ms and
the PGOOD pin goes to high impedance approximately
1.25ms after the FB pin voltage reaches 0.6V.
The PGOOD pin indicates when the converter is capable of
supplying regulated voltage. The PGOOD pin is an
undefined impedance if V
threshold V
V
capability that can drastically reduce trouble-shooting time
and effort. The pull-down resistance of the PGOOD pin
corresponds to the fault status of the controller. The PGOOD
pull-down resistance is 95Ω during soft-start or if an UVP
occurs, 30Ω for an OCP, or 60Ω for OVP.
MOSFET Gate-Drive Outputs LGATE and UGATE
The ISL6228 has internal gate-drivers for the high-side and
low-side N-Channel MOSFETs. The low-side gate-drivers
are optimized for low duty-cycle applications where the low-
side MOSFET conduction losses are dominant, requiring a
low r
small in order to clamp the gate of the MOSFET below the
V
turn-off can be considerable because the gate charge of a
low r
protection prevents a gate-driver output from turning on until
the opposite gate-driver output has fallen below
approximately 1V. The dead-time shown in Figure 4 is
extended by the additional period that the falling gate voltage
stays above the 1V threshold. The typical dead-time is 21ns.
The high-side gate-driver output voltage is measured across
the UGATE and PHASE pins while the low-side gate-driver
output voltage is measured across the LGATE and PGND
CCF
GS(th)
Soft-start or Undervoltage
DS(ON)
DS(ON)
. The ISL6228 features a unique fault-identification
VCC Below POR
at turnoff. The current transient through the gate at
TABLE 1. PGOOD PULL-DOWN RESISTANCE
CONDITION
Overvoltage
Overcurrent
CCR
FIGURE 3. SOFT-START SEQUENCE
MOSFET. The LGATE pull-down resistance is
MOSFET can be large. Adaptive shoot-through
, or if V
SS
1.5ms
begins and the output voltage begins to
CC
CC
is below the falling POR threshold
has not reached the rising POR
1.25ms
PGOOD RESISTANCE
Vo
EN
FB
PGOOD
VCC and PVCC
Undefined
90Ω
60Ω
30Ω
May 7, 2008
FN9095.2