ISL6564CR-T Intersil, ISL6564CR-T Datasheet - Page 25

• Manufacturer Part Number: ISL6564CR-T
• Description: IC CTRLR PWM MULTIPHASE 40-QFN
• Manufacturer: Intersil

Specifications of ISL6564CR-T

• Pwm Type: Voltage Mode
• Number Of Outputs: 1
• Frequency - Max: 1.5MHz
• Duty Cycle: 66.7%
• 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 ~ 70°C
• Package / Case: 40-VFQFN, 40-VFQFPN
• Frequency-max: 1.5MHz
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Input Supply Voltage Selection
The VCC input of the ISL6564 can be connected either
directly to a +5V supply or through a current limiting resistor
to a +12V supply. An integrated 5.8V shunt regulator
maintains the voltage on the VCC pin when a +12V supply is
used. A 300Ω resistor is suggested for limiting the current
into the VCC pin to a worst-case maximum of approximately
25mA.
Switching Frequency
There are a number of variables to consider when choosing
the switching frequency, as there are considerable effects on
the upper-MOSFET loss calculation. These effects are
outlined in MOSFETs, and they establish the upper limit for
the switching frequency. The lower limit is established by the
requirement for fast transient response and small output-
voltage ripple as outlined in Output Filter Design. Choose the
lowest switching frequency that allows the regulator to meet
the transient-response requirements.
Switching frequency is determined by the selection of the
frequency-setting resistor, R
Typical Application on pages 4, 5, 6 and 7). Figure
Equation 31 are provided to assist in selecting the correct
value for R
Input Capacitor Selection
The input capacitors are responsible for sourcing the ac
component of the input current flowing into the upper
MOSFETs. Their RMS current capacity must be sufficient to
handle the ac component of the current drawn by the upper
MOSFETs which is related to duty cycle and the number of
active phases.
R
T
1000
100
=
10
10
10
[
FIGURE 20. R
10.886 1.0792
T
.
–
SWITCHING FREQUENCY (kHz)
log
T
100
vs SWITCHING FREQUENCY
( )
f
S
]
T
25
(see the figures labeled
1000
23
(EQ. 30)
and
10000
ISL6564
For a two phase design, use Figure 24 to determine the
input-capacitor RMS current requirement given the duty
cycle, maximum sustained output current (I
of the per-phase peak-to-peak inductor current (I
Select a bulk capacitor with a ripple current rating which will
minimize the total number of input capacitors required to
support the RMS current calculated. The voltage rating of
the capacitors should also be at least 1.25 times greater
than the maximum input voltage.
Figures 24 and 25 provide the same input RMS current
information for three and four phase designs respectively.
Use the same approach to selecting the bulk capacitor type
and number as described above.
Low capacitance, high-frequency ceramic capacitors are
needed in addition to the bulk capacitors to suppress leading
and falling edge voltage spikes. The result from the high
current slew rates produced by the upper MOSFETs turn on
FIGURE 21. NORMALIZED INPUT-CAPACITOR RMS CURRENT
FIGURE 22. NORMALIZED INPUT-CAPACITOR RMS CURRENT
0.3
0.2
0.1
0.3
0.2
0.1
0
0
0
0
I
I
L,PP
L,PP
I
I
I
L,PP
L,PP
L,PP
= 0
= 0.25 I
= 0
= 0.5 I
= 0.75 I
vs DUTY CYCLE FOR 2-PHASE CONVERTER
vs DUTY CYCLE FOR 3-PHASE CONVERTER
0.2
0.2
O
O
O
DUTY CYCLE (V
DUTY CYCLE (V
0.4
0.4
I
I
L,PP
L,PP
= 0.5 I
= 0.75 I
0.6
0.6
O
O/
/V
V
O
IN
IN
O
)
)
O
), and the ratio
0.8
0.8
December 27, 2004
L,PP
) to I
FN9156.2
1.0
1.0
O
.