B340L MPS [Monolithic Power Systems], B340L Datasheet - Page 5

• Manufacturer Part Number: B340L
• Description: 2A, 32V, 330KHz Step-Down Converter
• Manufacturer: MPS [Monolithic Power Systems]

APPLICATION INFORMATION
COMPONENT SELECTION
Setting the Output Voltage
The output voltage is set using a resistive
voltage divider from the output voltage to FB.
The voltage divider divides the output voltage
down by the ratio:
Where V
the output voltage.
Thus the output voltage is:
A typical value for R2 can be as high as 100kΩ,
but 10kΩ is recommended. Using that value, R1
is determined by:
For example, for a 3.3V output voltage, R2 is
10kΩ, and R1 is 17kΩ.
Inductor (L1)
The inductor is required to supply constant
current to the output load while being driven by
the switched input voltage. A larger value
inductor results in less ripple current that results
in lower output ripple voltage. However, the
larger value inductor has a larger physical size,
higher
saturation current. Choose an inductor that
does not saturate under the worst-case load
conditions. A good rule to use for determining
the inductance is to allow the peak-to-peak
ripple
approximately 30% of the maximum load
current that the IC can provide. Also, make sure
that the peak inductor current (the load current
plus half the peak-to-peak inductor ripple
current) is below the 2.3A minimum current
limit.
MP1591 Rev. 2.3
9/27/2006
current
FB
series
is the feedback voltage and V
R
V
1
V
OUT
FB
≅
. 8
=
=
18
in
resistance,
V
. 1
OUT
×
230
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
(
V
the
×
OUT
×
R (
R (
1
−
R
1
inductor
+
R
. 1
+
2
R
2
230
R
) 2
and/or
) 2
)
© 2006 MPS. All Rights Reserved.
to
www.MonolithicPower.com
OUT
lower
be
MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER
is
The inductance value can be calculated by the
equation:
Where V
frequency and ∆I is the peak-to-peak inductor
ripple current.
Table 1 lists a number of suitable inductors
from various manufacturers.
Input Capacitor (C1)
The input current to the step-down converter is
discontinuous, and so a capacitor is required to
supply the AC current to the step-down
converter while maintaining the DC input
voltage. A low ESR capacitor is required to
keep the noise at the IC to a minimum. Ceramic
capacitors are preferred, but tantalum or low
ESR electrolytic capacitors may also suffice.
Sumida
CDRH5D28 Shielded
CDRH5D28 Shielded
CDRH6D28 Shielded
CDRH104R Shielded
Toko
Coilcraft
Vendor/
DO3308
DO3316
CDH74
D53LC
Type A
D104C
D10FL
Model
CR75
D75C
Table 1—Inductor Selection Guide
IN
is the input voltage, f is the switching
L
Shielded
Shielded
Shielded
1
Open
Open
Open
Open
Open
Type
Core
=
V
OUT
×
Material
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
Ferrite
(
(
Core
V
V
IN
IN
−
×
V
f
×
OUT
10.1 10.0 3.0
10.0 10.0 4.3
∆
7.0
7.6
9.7
9.4 13.0 3.0
9.4 13.0 5.1
7.3
5.5
5.5
6.7
5.0
W
) I
Dimensions
)
Package
(mm)
7.8
8.0
5.7
5.7
6.7
5.0
7.6
1.5
L
5.5
5.2
5.5
5.5
3.0
3.0
5.1
4.0
H
5