IR3651SPBF International Rectifier, IR3651SPBF Datasheet - Page 14

• Manufacturer Part Number: IR3651SPBF
• Description: IC CTLR SYNC PWM BUCK 14-SOIC
• Manufacturer: International Rectifier

Specifications of IR3651SPBF

• 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

Power MOSFET Selection
The IR3651 uses two N-Channel MOSFETs. The
selections criteria to meet power transfer
requirements is based on maximum drain-source
voltage (V
maximum output current, On-resistance R
and thermal management.
The MOSFET must have a maximum operating
voltage (V
voltage (V
The gate drive requirement is almost the same
for both MOSFETs. Logic-level transistor can be
used and caution should be taken with devices at
very low V
complementary MOSFET, which results in shoot-
through current.
The total power dissipation for MOSFETs
includes conduction and switching losses. For
the Buck converter the average inductor current
is equal to the DC load current. The conduction
loss is defined as:
The R
considered for the worst case operation. This is
typically given in the MOSFET data sheet.
Ensure that the conduction losses and switching
losses do not exceed the package ratings or
violate the overall thermal budget.
The switching loss is more difficult to calculate,
even though the switching transition is well
understood. The reason is the effect of the
parasitic components and switching times during
the switching procedures such as turn-on / turn-
off delays and rise and fall times. The control
MOSFET contributes to the majority of the
ϑ
P
P
12/07/2010
cond
cond
=
R
=
=
ds(on)
(upper
(lower
DS(on)
temperatur
in
DSS
gs
DSS
).
switch)
switch)
temperature dependency should be
to prevent undesired turn-on of the
), gate-source drive voltage (V
) exceeding the maximum input
=
e
=
I
I
load
2
load
2
dependency
∗
∗
R
R
ds(on)
ds(on)
∗
∗
(1
D
∗
−
ϑ
D)
∗
ϑ
DS(on)
gs
),
switching losses in synchronous Buck converter.
The synchronous MOSFET turns on under zero
voltage conditions, therefore, the turn on losses
for synchronous MOSFET can be neglected.
With a linear approximation, the total switching
loss can be expressed as:
Where:
V
t
t
T = Switching period
I
The switching time waveforms is shown in
figure10.
r
f
load
= Fall time
= Rise time
ds(off)
90%
10%
= Load current
V
V
GS
Fig. 10: switching time waveforms
DS
P
= Drain to source voltage at the off time
sw
t
d
(ON)
=
V
ds
2
(
off
)
*
t
r
T
+
t
t
r
f
*
I
load
t
IR3651SPBF
d
(OFF)
-
-(10)
t
f
14