ISL6558EVAL1Z Intersil, ISL6558EVAL1Z Datasheet - Page 5

• Manufacturer Part Number: ISL6558EVAL1Z
• Description: EVAL BOARD 1 FOR ISL6558
• Manufacturer: Intersil

Specifications of ISL6558EVAL1Z

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Equation 2 represents an individual channel’s
peak-to-peak inductor current. Equation 3 represents the
combined ripple current filtered by the output capacitors.
In Equation 3, m is the nearest integer that is rounded
up from the product of the number of active channels
and the individual channel duty cycle, and it represents
the maximum number of channels having positive slopes
within any time interval. In the reference design, m is
one. If the total ripple current (I
parameter K
ripple current multiplier (K
Equation 5, which is a function of channel duty cycle,
number of active channels, and m.
In addition to Equation 3, the total output ripple current
can be determined by the product of the ripple current
multiplier (K
normalization factor, K
The RMS and peak currents through the single-channel
inductor are defined in Equations 6 and 7, respectively.
As a rule of thumb, the total output ripple current should
set around 10% to 20% of full load; the required channel
inductor value then can be derived from Equation 3,
rearranged in Equation 8.
FIGURE 4. RIPPLE CURRENT MUTIPLIER VS. DUTY
I
K
I
K
PP
Lo PP
NORM
CM
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
,
=
1
0
where
=
------------------------
Lo Fsw
0
for
=
(
--------------------------------------------------------------------------- -
•
=
N D
V
V
------------------------------ -
1
0.1
L o Fsw
•
1
------------------------
Lo Fsw
CM
NORM
•
•
(
V
•
–
⎛
⎝
1 D
) read from Figure 4 and the
(
--------------------------------------------------------------------------- -
1
0.2
m
–
N D
+
•
N D
, i.e, I
3
V
m 1
2
)
1
m
DUTY CYCLE (V
•
1
0.3
)
–
–
=
•
=
m
(
NORM
Vo
m N D
≤
ROUNDUP N D
Lo,PP
+
N D
0.4
N D
–
+
1
N=1
CM
•
•
)
5
Io
---- -
N
.
•
•
(
0.5
at zero duty cycle, then the
) can be defined as in
•
≤
m N D
(
)
m
R
–
PP
Q1
O
(
0.6
) is normalized to the
/V
•
+
•
IN
R
)
Lo
⎞
⎠
0.7
)
,
0
+
)
Application Note 1029
R
0.8
Bo
)
4
0.9
(EQ. 4)
(EQ. 5)
(EQ. 2)
(EQ. 3)
1
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 individual channel, as defined in
Equation 3, and its RMS value is defined in Equation 9.
Besides being able to handle the heat that is generated
by their equivalent series resistance (ESR), the output
capacitors should be designed to meet the output voltage
ripple and load transient requirements. For high dI/dt
loads, the output voltage ripple will be within the limits
when the requirements for the load transient are met.
The output voltage ripple can be conservatively
approximated by Equation 10. The first two terms
(dV
resistance (ESR) and the equivalent series inductance
(ESL) of the output capacitors are the dominant ones and
are normally accurate enough to estimate the ripple
voltage. The last term (dV
capacitance (Co) is normally much smaller and can be
neglected since the peak of the dV
ripple current zero crossing and does not align with the
peak of dV
FIGURE 5. OUTPUT VOLTAGE RIPPLE COMPONENTS
Vo
dV
dV
dV
Lo
I
I
Io
Lo RMS
Lo PEAK
RIPPLE
ESR
ESL
RMS
Co
ESR
,
,
=
0
0
-------------------------- -
I
0
PP
=
and dV
=
V
≈
•
=
I
-------- -
1
ESR
Fsw
12
I
2
PP
PP
Io
---- -
N
⎛ ⎞
⎝ ⎠
Io
---- -
N
+
, as shown in Figure 5.
•
ESL
⎛
⎝
(
--------------------------------------------------------------------------- -
-
ESR
I
----------------- -
+
2
Lo PP
+
N D
+
2
) contributed by the equivalent series
,
•
I
----------------- -
2
Lo PP
+
12
–
,
ESL
----------- - V
Lo
m
+
N D
•
1
Co
•
)
•
) contributed by the output
IN
(
-
-
dV
m N D
-
+
------- -
Co
–
Co
dV ESR
1
dV
Co
•
•
=
ESL
------------------------------ -
8 N
------- -
Co
happens at the
1
•
)
⎞
⎠
=
•
I
=
PP
I PP E
-------------------------------
8 N
•
ESL
----------- - V
•
Fsw
L
I
•
PP
•
•
Fsw
(
(EQ. 10)
d
July 31, 2009
IN
(EQ. 6)
(EQ. 8)
(EQ. 9)
S
(EQ. 7)
)R
AN1029.3