IR3876TR1PbF IRF [International Rectifier], IR3876TR1PbF Datasheet - Page 15

• Manufacturer Part Number: IR3876TR1PbF
• Description: 12A HIGHLY INTEGRATED WIDE-INPUT VOLTAGE, SYNCHRONOUS BUCK REGULATOR
• Manufacturer: IRF [International Rectifier]

Find R
DESIGN EXAMPLE
Design Criteria:
Input Voltage, VIN, = 7V to 16V
Output Voltage, VOUT = 1.05V
Switching Frequency, Fs = 300KHz
Inductor Ripple Current, 2ΔI = 3A
Maximum Output Current, IOUT = 12A
Over Current Trip, IOC = 18A
Overshoot Allowance, VOS = VOUT + 50mV
Undershoot Allowance, VDROP = 50mV
Pick a standard value 178 kΩ, 1% resistor.
Find R
Choose the soft start capacitor:
Once the soft start time has chosen, such as
1000us to reach to the reference voltage, a 22nF
for C
Choose an inductor to meet the design
specification:
R
The R
expected to increase by a factor of 1.4 over
temperature.
standard resistor.
Find a resistive voltage divider for V
R
resistors.
R
V
L
2
FF
SET
FB
= 2.55kΩ, R




SS
1.1

1.05
V

1
6 1
FF
SET
V
DSON
R
OUT
is used to meet 1000us.
1.4

V
:
V
R
2

V
H
:

20
IN
2





3
5
R
V


of the lower MOSFET could be
1.05
2
6 1
pF
2 .
A
1
IN
ΔI
1
20


m
V
Therefore, pick a 6.65kΩ, 1%
= 2.80kΩ, both 1% standard
300K
V




V

300K
V
-
OUT
F
1.05
A
OUT
s

18

Hz

V
Hz
A
0.5

V

175

6.55K
K
OUT


= 1.05V:
I
Choose an input capacitor:
IN_RMS
A
accommodates 6 Arms of ripple current at
300KHz. Due to the chemistry of multilayer
ceramic capacitors, the capacitance varies over
temperature and operating voltage, both AC and
DC. One 10µF capacitor is recommended. In a
practical solution, one 1µF capacitor is required
along with the 10µF. The purpose of the 1µF
capacitor is to suppress the switching noise and
deliver high frequency current.
Choose an output capacitor:
To meet the undershoot specification, select a
set of output capacitors which has an equivalent
ESR of 10mΩ (50mV/5A). To meet the
overshoot specification, equation 7 will be used
to calculate the minimum output capacitance. As
a result, 300µF will be needed for 5A load
removal. Combine those two requirements, one
can choose a set of output capacitors from
manufactures such as Sanyo or Rubycon. A
330µF (2SWZ330M R05) from Rubycon is
recommended. This capacitor has 4.5mΩ ESR
which leaves margin for the voltage drop of the
ESL during load step up.
Choose an inductor with the lowest DCR and
AC power loss as possible to increase the
overall system efficiency. For instance, choose
MPL1055-1R21R manufactured by Delta. The
inductance of this part is 1.2µH and has 2.9mΩ
DCR. Ripple current needs to be recalculated
using the chosen inductor.
ΔI
Panasonic



2 1
3.1
2
A

A
1.05
6 1

V
1.05
V
16

. 1

V

u 2
6 1
V
10µF
H
V


-
1
300K
1.05

IR3876MBF
1
3
V
(ECJ3YB1E106M)




Hz

. 1
2 1
36

A
1.36
A



2
A
15