IR3856MTRPBF International Rectifier, IR3856MTRPBF Datasheet - Page 20

• Manufacturer Part Number: IR3856MTRPBF
• Description: IC BUCK SYNC ADJ 6A 17PQFN
• Manufacturer: International Rectifier
• Series: SupIRBuck™r
• Type: Step-Down (Buck)r

Specifications of IR3856MTRPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.7 ~ 18.9 V
• Current - Output: 6A
• Frequency - Switching: 250kHz ~ 1.5MHz
• Voltage - Input: 1.5 ~ 21 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 17-PowerVQFN
• Power - Output: 1.11W
• Primary Input Voltage: 21V
• No. Of Outputs: 1
• Output Voltage: 18.9V
• Output Current: 6A
• No. Of Pins: 17
• Operating Temperature Range: -40°C To +125°C
• Peak Reflow Compatible (260 C): Yes
• Rohs Compliant: Yes
• Leaded Process Compatible: Yes
• Part Status: Preferred
• Package: PQFN / 4 x 5
• Circuit: Single Output
• Iout (a): 6
• Switch Freq (khz): 250 - 1500
• Input Range (v): 1.5 - 21
• Output Range (v): 0.7 - 0.9*Vin
• Ocp Otp Uvlo Pre-bias Soft Start And: PGOOD + EN + SEQ + OVP + SYNC
• Design Tool: Yes
• Server Storage: Yes
• Routers Switches: Yes
• Base Station Telecom: Yes
• Digital Home Media: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

across C6 remains approximately unchanged and
the voltage at the Boot pin becomes:
A bootstrap capacitor of value 0.1uF is suitable
for most applications.
Input Capacitor Selection
The ripple current generated during the on time of
the upper MOSFET should be provided by the
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 I
Ceramic capacitors are recommended due to
their peak current capabilities. They also feature
low ESR and ESL at higher frequency which
enables better efficiency. For this application, it is
advisable to have 3x10uF 25V ceramic capacitors
C3216X5R1E106M from TDK. In addition to
these, although not mandatory, a 1X330uF, 25V
SMD capacitor EEV-FK1E331P may also be
used as a bulk capacitor and is recommended if
the input power supply is not located close to the
converter.
RMS
V
Rev2.0
Boot
I
D =
Fig. 13. Bootstrap circuit to generate
RMS
o
is the RMS value of the input capacitor
=6A and D = 0.15, the I
≅
V
V
V
=
in
in
o
I
+
..........
o
V
∗
cc
D
−
V
..........
∗
Vc voltage
D
(
1
..........
−
D
..........
)
..........
..........
RMS
..
(14)
..........
..........
= 2.14A.
..........
....(13)
(12)
Inductor Selection
The inductor is selected based on output power,
operating frequency and efficiency requirements.
A 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 the inductor
value can be reduced to the desired maximum
ripple current in the inductor (
point is usually found between 20% and 50%
ripple of the output current.
For the buck converter, the inductor value for the
desired
determined using the following relation:
Where:
If
calculated to be 1.01μH. Select L=1.0 μH.
The SPM6550T-1R0M from TDK provides a
compact inductor suitable for this application.
V
in
L
−
Δi ≈ 43%(I
=
V
(
o
V
V
V
F
D
Δi
Δt
in
=
in
o
s
=
operating
=
L
−
=
=
=
=
Duty
V
∗
Switching
Inductor
Output
Turn
Maximum
o
Δ
Δ
)
t
i
∗
;
V
o
cycle
), then the output inductor is
on
in
Δ
∗
t
Voltage
V
ripple
Δ
time
=
o
* i
frequency
ripple
D
IR3856MPbF
input
F
∗
s
F
current
1
s
voltage
..........
Δ
current
i ) . The optimum
PD-97528
..........
can
...
(15)
20
be