Microchip Technology ARD00386 Data Sheet
MCP1640/B/C/D
DS22234B-page 16
2011 Microchip Technology Inc.
5.5
Inductor Selection
The MCP1640/B/C/D is designed to be used with small
surface mount inductors; the inductance value can
range from 2.2 µH to 10 µH. An inductance value of
4.7 µH is recommended to achieve a good balance
between inductor size, converter load transient
response and minimized noise.
surface mount inductors; the inductance value can
range from 2.2 µH to 10 µH. An inductance value of
4.7 µH is recommended to achieve a good balance
between inductor size, converter load transient
response and minimized noise.
Several parameters are used to select the correct
inductor: maximum rated current, saturation current
and copper resistance (ESR). For boost converters, the
inductor current can be much higher than the output
current. The lower the inductor ESR, the higher the
efficiency of the converter, a common trade-off in size
versus efficiency.
inductor: maximum rated current, saturation current
and copper resistance (ESR). For boost converters, the
inductor current can be much higher than the output
current. The lower the inductor ESR, the higher the
efficiency of the converter, a common trade-off in size
versus efficiency.
Peak current is the maximum or limit, and saturation
current typically specifies a point at which the induc-
tance has rolled off a percentage of the rated value.
This can range from a 20% to 40% reduction in induc-
tance. As inductance rolls off, the inductor ripple cur-
rent increases as does the peak switch current. It is
important to keep the inductance from rolling off too
much, causing switch current to reach the peak limit.
current typically specifies a point at which the induc-
tance has rolled off a percentage of the rated value.
This can range from a 20% to 40% reduction in induc-
tance. As inductance rolls off, the inductor ripple cur-
rent increases as does the peak switch current. It is
important to keep the inductance from rolling off too
much, causing switch current to reach the peak limit.
5.6
Thermal Calculations
The MCP1640/B/C/D is available in two different
packages, 6-Lead SOT23 and 8-Lead 2x3 DFN. By cal-
culating the power dissipation and applying the pack-
age thermal resistance, (
packages, 6-Lead SOT23 and 8-Lead 2x3 DFN. By cal-
culating the power dissipation and applying the pack-
age thermal resistance, (
JA
), the junction temperature
is estimated. The maximum continuous junction
temperature rating for the MCP1640/B/C/D is +125
temperature rating for the MCP1640/B/C/D is +125
o
C.
To quickly estimate the internal power dissipation for
the switching boost regulator, an empirical calculation
using measured efficiency can be used. Given the
measured efficiency, the internal power dissipation is
estimated by
the switching boost regulator, an empirical calculation
using measured efficiency can be used. Given the
measured efficiency, the internal power dissipation is
estimated by
.
EQUATION 5-3:
The difference between the first term – input power,
and the second term – power delivered, is the internal
MCP1640/B/C/D power dissipation. This is an esti-
mate, assuming that most of the power lost is internal
to the MCP1640/B/C/D and not C
and the second term – power delivered, is the internal
MCP1640/B/C/D power dissipation. This is an esti-
mate, assuming that most of the power lost is internal
to the MCP1640/B/C/D and not C
IN
, C
OUT
and the
inductor. There is some percentage of power lost in the
boost inductor, with very little loss in the input and out-
put capacitors. For a more accurate estimation of inter-
nal power dissipation, subtract the I
boost inductor, with very little loss in the input and out-
put capacitors. For a more accurate estimation of inter-
nal power dissipation, subtract the I
INRMS
2
*L
ESR
power
dissipation.
5.7
PCB Layout Information
Good printed circuit board layout techniques are
important to any switching circuitry; and, switching
power supplies are no different. When wiring the
switching high current paths, short and wide traces
should be used. Therefore it is important that the input
and output capacitors be placed as close as possible to
the MCP1640/B/C/D to minimize the loop area.
important to any switching circuitry; and, switching
power supplies are no different. When wiring the
switching high current paths, short and wide traces
should be used. Therefore it is important that the input
and output capacitors be placed as close as possible to
the MCP1640/B/C/D to minimize the loop area.
TABLE 5-2:
MCP1640/B/C/D
RECOMMENDED INDUCTORS
RECOMMENDED INDUCTORS
Part Number
Value
(µH)
DCR
(typ)
I
SAT
(A)
Size
WxLxH
(mm)
Coilcraft
®
EPL2014-472
4.7
0.23
1.06
2.0x2.0x1.4
EPL3012-472
4.7
0.165
1.1
3.0x3.0x1.3
MSS4020-472
4.7
0.115
1.5
4.0x4.0x2.0
LPS6225-472
4.7
0.065
3.2
6.0x6.0x2.4
Coiltronics
®
SD3110
4.7
0.285
0.68
3.1x3.1x1.0
SD3112
4.7
0.246
0.80
3.1x3.1x1.2
SD3114
4.7
0.251
1.14
3.1x3.1x1.4
SD3118
4.7
0.162
1.31
3.8x3.8x1.2
SD3812
4.7
0.256
1.13
3.8x3.8x1.2
SD25
4.7
0.0467
1.83
5.0x5.0x2.5
Part Number
Value
(µH)
DCR
(max)
I
SAT
(A)
Size
WxLxH
(mm)
Wurth Elektronik
®
WE-TPC Type
TH
TH
4.7
0.200
0.8
2.8x2.8x1.35
WE-TPC Type
S
S
4.7
0.105
0.90
3.8x3.8x1.65
WE-TPC Type
M
M
4.7
0.082
1.65
4.8x4.8x1.8
WE-TPC Type
X
X
4.7
0.046
2.00
6.8x6.8x2.3
Part Number
Value
(µH)
DCR
(max)
I
SAT
(A)
Size
WxLxH
(mm)
Sumida
®
CMH23
4.7
0.537
0.70
2.3x2.3x1.0
CMD4D06
4.7
0.216
0.75
3.5x4.3x0.8
CDRH4D
4.7
0.09
0.800
4.6x4.6x1.5
EPCOS
®
B82462A2472
M000
M000
4.7
0.084
2.00
6.0x6.0x2.5
B82462G4472
M
M
4.7
0.04
1.8
6.3x6.3x3.0
V
OUT
I
OUT
Efficiency
-------------------------------------
V
OUT
I
OUT
–
P
Dis
=