ISL6563 Intersil Corporation, ISL6563 Datasheet - Page 8

• Manufacturer Part Number: ISL6563
• Description: Two-Phase Multi-Phase Buck PWM Controller with Integrated MOSFET Drivers
• Manufacturer: Intersil Corporation

Assuming identical power switch selection on the two
channels, the following equation determines the current fed
out the FB pin for output voltage droop generation:
where, r
I
Multi-Phase Power Conversion
Multi-phase power conversion provides a cost-effective
power solution when load currents are no longer easily
supported by single-phase converters. Although its greater
complexity presents additional technical challenges, the
multi-phase approach offers cost-saving advantages with
improved response time, superior ripple cancellation, and
thermal distribution.
INTERLEAVING
The switching of each channel in a ISL6563-based converter
is timed to be symmetrically out of phase with the other
channel. As a result, the two-phase converter has a
combined ripple frequency twice the frequency of one of its
phases. In addition, the peak-to-peak amplitude of the
combined inductor currents is proportionately reduced.
Increased ripple frequency and lower ripple amplitude
generally translate to lower per-channel inductance and
lower total output capacitance for a given set of performance
specifications.
Figure 2 illustrates the additive effect on output ripple
frequency. The two channel currents (I
to form the AC ripple current and the DC load current. The
ripple component has two times the ripple frequency of each
individual channel current.
I
PHASE
FB
FIGURE 2. PWM AND INDUCTOR-CURRENT WAVEFORMS
=
r
----------------------------------------------- -
DS ON
DS(ON)
- average phase current
(
R
PWM1
ISEN
)
FOR 2-PHASE CONVERTER
⋅
I
- lower MOSFET/s’ ON resistance (@5V)
PHASE
I
L1
PWM2
I
L2
8
I
L1
L1
+ I
and I
L2
L2
), combine
ISL6563
ISL6563
To understand the reduction of ripple current amplitude in
the multi-phase circuit, examine the equation representing
an individual channel’s peak-to-peak inductor current.
V
respectively, L is the single-channel inductor value, and f
the switching frequency.
The output capacitors conduct the ripple component of the
inductor current. In the case of multi-phase converters, the
capacitor current is the sum of the ripple currents from each
of the individual channels. Peak-to-peak ripple current, I
decreases by an amount proportional to the number of
channels. Output-voltage ripple is a function of capacitance,
capacitor equivalent series resistance (ESR), and inductor
ripple current. Reducing the inductor ripple current allows
the designer to use fewer or less costly output capacitors
(should output ripple be an important design parameter).
Another benefit of interleaving is the reduction of input ripple
current. Input capacitance is determined in a large part by
the maximum input ripple current. Multi-phase topologies
can improve overall system cost and size by lowering input
ripple current and allowing the designer to reduce the cost of
input capacitance. The example in Figure 3 illustrates input
currents from a two-phase converter combining to reduce
the total input ripple current.
I
I
PP
L PP
IN
,
FIGURE 3. INPUT CAPACITOR CURRENT AND INDIVIDUAL
=
and V
(
------------------------------------------------------------------- -
=
V
IN
(
--------------------------------------------------------- -
V
OUT
–
IN
N V
L f
–
L f
C
CHANNEL CURRENTS IN A 2-PHASE
CONVERTER
⋅
⋅
V
IN
⋅
are the input and output voltages,
OUT
S
S
OUT
CURRENT
⋅
⋅
V
V
) V
IN
) V
IN
⋅
⋅
OUT
OUT
Q1 D-S CURRENT
Q3 D-S CURRENT
PP
S
is
,