ISL6556BCBZ Intersil, ISL6556BCBZ Datasheet - Page 21

• Manufacturer Part Number: ISL6556BCBZ
• Description: IC CTRLR MULTIPHASE VRM10 28SOIC
• Manufacturer: Intersil

Specifications of ISL6556BCBZ

• 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: 28-SOIC (7.5mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Input Supply Voltage Selection
The VCC input of the ISL6556B 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 and 5). Figure 13 and
Equation 27 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.
For a two phase design, use Figure 14 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
R
T
1000
100
=
10
1.0203 10
10
FIGURE 13. R
T
.
(
)
[
10.6258- 1.03167
SWITCHING FREQUENCY (kHz)
T
100
vs SWITCHING FREQUENCY
(
·
T
21
(see the figures labeled
)
log
( )
f
S
]
–
1000
1200
O
), and the ratio
L,PP
(EQ. 27)
) to I
10000
O
ISL6556B
.
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 15 and 16 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
and off. Select low ESL ceramic capacitors and place one as
close as possible to each upper MOSFET drain to minimize
board parasitic impedances and maximize suppression.
FIGURE 14. NORMALIZED INPUT-CAPACITOR RMS CURRENT
FIGURE 15. 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
O
IN
)
)
0.8
0.8
December 28, 2004
FN9097.4
1.0
1.0