ISL6569ACR Intersil, ISL6569ACR Datasheet - Page 15

• Manufacturer Part Number: ISL6569ACR
• Description: IC CTRLR PWM BUCK 2PHASE 32-QFN
• Manufacturer: Intersil

Specifications of ISL6569ACR

• Pwm Type: Voltage/Current Mode
• Number Of Outputs: 1
• Frequency - Max: 2MHz
• Duty Cycle: 75%
• Voltage - Supply: 4.75 V ~ 5.25 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: 0°C ~ 85°C
• Package / Case: 32-VQFN Exposed Pad, 32-HVQFN, 32-SQFN, 32-DHVQFN
• Frequency-max: 2MHz
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

impedance state. The Intersil drivers respond by turning off
both upper and lower MOSFETs. If the over-voltage condition
reoccurs, the ISL6569A will again command the lower
MOSFETs to turn on. The ISL6569A will continue to protect
the load in this fashion as long as the over-voltage repeats.
Second, the OVP pin pulls to VCC and can deliver 100mA
into the gate of either a MOSFET or SCR placed on the input
rail (V
collapses the power rail and causes a fuse placed further up
stream to blow. The fuse must be sized such that the
MOSFET or SCR will not overheat before the fuse blows.
Once an over-voltage condition is detected, normal PWM
operation ceases and PGOOD remains low until the
ISL6569A is reset. Cycling the voltage on EN below 1.23V or
the bias to VCC below the POR-falling threshold will reset
the controller.
Over-Current Protection
The ISL6569A takes advantage of the proportionality
between the load current and the average current, I
detect an over-current condition. See the Channel-Current
Balance section for more detail on how the average current
is created. The average current is continually compared with
a constant 90µA reference current. Once the average
current exceeds the reference current, the comparator
triggers the converter to shutdown. The POR circuit places
all PWM signals in a high-impedance state which commands
the drivers to turn off both upper and lower MOSFETs.
PGOOD pulls low and the system remains in this state while
the controller counts 2048 phase clock cycles. This is
followed by a soft-start attempt (see Soft-Start).
During the soft-start interval, the over-current protection
circuitry remains active. As the output voltage ramps up, if an
over-current condition is detected, the ISL6569A
immediately places all PWM signals in a high-impedance
state. The ISL6569A repeats the 2048-cycle wait period and
follows with another soft-start attempt, as shown in
Figure 12. This hiccup mode of operation repeats up to
seven times. On the eighth soft-start attempt, the part
latches off. Once latched off, the ISL6559 can only be reset
when the voltage on EN is brought below 1.23V or VCC is
brought below the POR falling threshold. Upon completion of
a successful soft-start attempt, operation will continue as
normal, PGOOD will return high, and the over-current latch
counter will reset.
During VID-on-the-fly transitions, the OC comparator output
is blanked. The quality and mix of output capacitors used in
different applications leads to a wide output capacitance
range. Depending upon the magnitude and direction of the
VID change, the change in voltage across the output
capacitors could result in significant current flow. Summing
this instantaneous current with the load current already
present could drive the average current above the reference
current level and cause an OC trip during the transition. By
IN
) or V
OUT
. Turning on the MOSFET or SCR
15
AVG
, to
ISL6569A
blanking the OC comparator during the VID-on-the-fly
transition, nuisance tripping is avoided.
General Design Guide
This design guide is intended to provide a high-level
explanation of the steps necessary to create a multi-phase
power converter. It is assumed that the reader is familiar with
many of the basic skills and techniques referenced below. In
addition to this guide, Intersil provides complete reference
designs that include schematics, bills of materials, and
example board layouts for all common microprocessor
applications.
Power Stages
Principally, the designer will be concerned with whether
components can be mounted on both sides of the circuit
board; whether through-hole components are permitted; and
the total board space available for power-supply circuitry.
Generally speaking, the most economical solutions are
those where each phase handles between 15 and 20A. All
surface-mount designs will tend toward the lower end of this
current range and, if through-hole MOSFETs can be used,
higher per-phase currents are possible. In cases where
board space is the limiting constraint, current can be pushed
as high as 30A per phase, but these designs require heat
sinks and forced air to cool the MOSFETs.
MOSFETs
The choice of MOSFETs depends on the current each
MOSFET will be required to conduct; the switching frequency;
the capability of the MOSFETs to dissipate heat; and the
availability and nature of heat sinking and air flow.
LOWER MOSFET POWER CALCULATION
The calculation for heat dissipated in the lower MOSFET is
simple, since virtually all of the heat loss in the lower
MOSFET is due to current conducted through the channel
resistance (r
continuous output current; I
FIGURE 12. OVERCURRENT BEHAVIOR IN HICCUP MODE
0A
0V
DS(ON)
). In Equation 13, I
PP
5ms/DIV
OUTPUT CURRENT, 20A/DIV
is the peak-to-peak inductor
OUTPUT VOLTAGE,
500mV/DIV
M
is the maximum
December 29, 2004
FN9092.2