IR3651STRPBF International Rectifier, IR3651STRPBF Datasheet - Page 13

• Manufacturer Part Number: IR3651STRPBF
• Description: IC CTLR PWM SYNC DC-DC 14SOIC
• Manufacturer: International Rectifier

Specifications of IR3651STRPBF

• Pwm Type: Voltage Mode
• Number Of Outputs: 1
• Frequency - Max: 460kHz
• Duty Cycle: 80%
• Voltage - Supply: 4.5 V ~ 13.2 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: 0°C ~ 125°C
• Package / Case: 14-SOIC (3.9mm Width), 14-SOL
• Frequency-max: 460kHz
• Package: 14-Pin SOIC (NB)
• Circuit: Sync PWM Controller
• Vcc (min): 4.5
• Vcc (max): 13.2
• Iout (a): 25
• Switch Freq (khz): programmable to 400kHz
• Pbf: PbF Option Available
• For Use With: IRDC3651 - KIT REF DESIGN SYNCH BUCK REG
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

L
Input Capacitor Selection
The input filter capacitor should be selected
based on how much ripple the supply can
tolerate on the DC input line. The ripple current
generated during the on time of upper MOSFET
should be provided by input capacitor. The RMS
value of this ripple is expressed by:
Where:
D is the Duty Cycle
I
current.
Io is the output current.
For applications with input supplies above 30V,
choice of input capacitor type is limited to
ceramics or aluminum electrolytics. Ceramic
capacitors offer high peak current capabilities,
they also feature low ESR and ESL at higher
frequency which enhance better efficiency,
however high voltage ceramic capacitors are
available with only in low value capacitance. A
combination
electrolytic capacitors are recommended.
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:
V
V
I
Δ
F
Δ
D
RMS
12/07/2010
V
RMS
in
o
=
i
t
s
in
=
=
=
=
(
=
=
−
V
=
Switching
Duty
Output
Turn
V
in
Inductor
Maximum
is the RMS value of the input capacitor
I
o
−
o
=
∗
V
o
L
cycle
)
on
operating
D
∗
∗
V
Voltage
Δ
Δ
∗
time
in
i
t
( −
ripple
1
;
∗
frequency
input
of
V
Δ
Δ
o
i
D
t
*
=
)
F
current
D
s
voltage
ceramic
--(
( i
ripple
∗
Δ
--(
F
1
) 7
s
)
) 8
. The optimum point is
current
capacitors
D =
V
V
can
in
o
and
be
Output Capacitor Selection
The voltage ripple and transient requirements
determine 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:
Since the output capacitor has major role in
overall performance of converter and determines
the result of transient response, selection of
capacitor is critical. The IR3651 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.
In the case of tantalum or low ESR electrolytic
capacitors, the ESR dominates the output
voltage ripple, equation (9) can be used to
calculate the required ESR for the specific
voltage ripple.
Δ
Δ
Δ
Δ
Δ
Δ
V
V
V
V
V
I
L
o
o
o
o
o
(
(
(
=
C
ESR
ESL
=
=
)
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
+
-(9)
Δ
V
IR3651SPBF
o
(
C
)
are other
13