IR3623MPBF_1 IRF [International Rectifier], IR3623MPBF_1 Datasheet - Page 18

• Manufacturer Part Number: IR3623MPBF_1
• Description: HIGH FREQUENCY 2-PHASE, SINGLE OR DUAL OUTPUT SYNCHRONOUS STEP DOWN CONTROLLER WITH OUTPUT TRACKING AND SEQUENCING
• Manufacturer: IRF [International Rectifier]

Inductor Selection
The inductor is selected based on output power,
operating frequency and efficiency requirements.
Low inductor value causes large ripple current,
resulting in the smaller size, faster response to a
load transient but poor efficiency and high output
noise. Generally, the selection of inductor value
can be reduced to desired maximum ripple
current in the inductor
usually found between 20% and 50% ripple of
the output current.
For the buck converter, the inductor value for
desired
determined using the following relation:
Where:
For 2-phase single output application the inductor
ripple current is chosen between 10-40% of
maximum phase current
If
L = 0.37uH
The Panasonic ETQP4LR36WFC (L
24A, R
inductor suitable for this application.
Use the following equation to calculate C
R
This results to C
www.irf.com
V
V
Δ
F
Δ
D
12
Δ
in
o
i
t
s
=
=
i ≈
=
=
=
=
for current sensing:
Switching
Duty
Output
Inductor
Turn
Maximum
35
L
L1
%(
=
=1.1mOhm) provides a low profile
operating
cycle
on
R
V
I
(
o
V
in
Voltage
12
)
in
time
−
, then the output inductor will be:
ripple
−
*
V
frequency
input
V
o
C
12
o
=
12
=0.33uF and R
)
∗
L
V
current
=
∗
voltage
in
Δ
ripple
Δ
( i
R
∗
Δ
i
t
L
V
Δ
;
1
L
o
1
)
i
Δ
*
. The optimum point is
t
F
s
=
current
D
∗
-
12
F
- -
1
=1.1K
s
( -
12
1
=0.34uH,
can
)
12
and
be
Output Capacitor Selection
The voltage ripple and transient requirements
determines the output capacitors types and
values. The criteria is normally based on the
value of the Effective Series Resistance (ESR).
However the actual capacitance value and the
Equivalent Series Inductance (ESL)
contributing components, these components can
be described as:
Δ
Δ
Δ
Δ
Δ
Δ
Since the output capacitor has major role in
overall performance of converter and determine
the result of transient response, selection of
capacitor is critical. The IR3623 can perform well
with all types of capacitors.
As a rule the capacitor must have low enough
ESR to meet output ripple and load transient
requirements, yet have high enough ESR to
satisfy stability requirements.
The goal for this design is to meet the voltage
ripple requirement in smallest possible capacitor
size. Therefore ceramic capacitor is selected due
to low ESR and small size.
Panasonic ECJ2FB0J226M (22uF, 6.3V, X5R
and EIA 0805 case size) is a good choice.
In the case of tantalum or low ESR electrolytic
capacitors, the ESR dominates the output
voltage ripple, equation (13) can be used to
calculate the required ESR for the specific
voltage ripple.
V
V
V
V
V
I
L
o
o
o
o
o
(
(
(
=
ESR
ESL
C
=
=
)
Inductor
Output
=
Δ
)
)
V
=
=
8
o
⎛
⎜
⎝
(
Δ
*
ESR
V
I
L
C
Δ
L
in
)
I
o
*
⎞
⎟
⎠
L
+
*
voltage
ESR
*
ripple
F
Δ
ESL
s
V
o
(
ESL
current
)
ripple
-
+
- -
Δ
V
-(13)
o
IR3623MPbF
(
C
)
are other
18