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M2305SDS View Datasheet(PDF) - Unspecified

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M2305SDS Datasheet PDF : 12 Pages
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MP2305S – 2A, 23V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER
APPLICATIONS INFORMATION
COMPONENT SELECTION
Setting the Output Voltage
The output voltage is set using a resistive voltage
divider from the output voltage to FB pin. The
voltage divider divides the output voltage down to
the feedback voltage by the ratio:
VFB
=
VOUT
R2
R1+ R2
Where VFB is the feedback voltage and VOUT is
the output voltage.
Thus the output voltage is:
VOUT
=
0.923
×
R1 + R2
R2
R2 can be as high as 100k, but a typical value
is 10k. Using the typical value for R2, R1 is
determined by:
R1 = 10.83 × (VOUT 0.923) (k)
larger value inductor will have a larger physical
size, higher series resistance, and/or lower
saturation current.
A good rule for determining the inductance to use
is to allow the peak-to-peak ripple current in the
inductor to be approximately 30% of the
maximum switch current limit. Also, make sure
that the peak inductor current is below the
maximum switch current limit. The inductance
value can be calculated by:
L
=
VOUT
fS × ΔIL
× ⎜⎜⎝⎛1
VOUT
VIN
⎟⎟⎠⎞
Where VOUT is the output voltage, VIN is the input
voltage, fS is the switching frequency, and ΔIL is
the peak-to-peak inductor ripple current.
Choose an inductor that will not saturate under
the maximum inductor peak current. The peak
inductor current can be calculated by:
For example, for a 3.3V output voltage, R2 is
10k, and R1 is 26.1k.
ILP
= ILOAD
+
VOUT
2 × fS × L
× ⎜⎜⎝⎛1
VOUT
VIN
⎟⎟⎠⎞
Inductor
The inductor is required to supply constant
current to the output load while being driven by
the switched input voltage. A larger value
inductor will result in less ripple current that will
result in lower output ripple voltage. However, the
where ILOAD is the load current.
Table 1 lists a number of suitable inductors from
various manufacturers. The choice of which style
inductor to use mainly depends on the price vs.
size requirements and any EMI requirement.
Table 1—Inductor Selection Guide
Part Number
Inductance (µH) Max DCR () Current Rating (A)
Wurth Electronics
7440650068
6.8
0.033
3.6
744066100
10
0.035
3.6
744066150
15
0.050
3.2
TDK
SLF10165T-6R8N4R33PF
6.8
0.014
4.3
SLF10165T-100M3R83PF
10
0.0185
3.8
SLF10165T-150M3R13PF
15
0.027
3.1
Toko
#B952AS-6R8N
6.8
0.035
3.1
#B892NAS-100M
10
0.0225
4.2
#B892NAS-150M
15
0.0355
3.2
Dimensions
L x W x H (mm3)
10x10x2.8
10x10x3.8
10x10x3.8
10x10x4.5
10x10x4.5
10x10x4.5
10.4x10.4x4.8
12.3x12.3x4.5
12.3x12.3x4.5
MP2305S Rev. 1.02
www.MonolithicPower.com
7
10/22/2013
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
 

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