MCP1640_13 Datasheet, PDF (16/32 Pages) Microchip Technology – 0.65V START-UP SYNCHRONOUS BOOST REGULATOR WITH TRUE OUTPUT DISCONNECT OR INPUT/OUTPUT BYPASS OPTION

MCP1640/B/C/D
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.
TABLE 5-2: MCP1640/B/C/D
RECOMMENDED INDUCTORS
Part Number
Value DCR
(µH)  (typ)
I_SAT
(A)
Coilcraft^®
EPL2014-472 4.7 0.23 1.06
EPL3012-472 4.7 0.165 1.1
MSS4020-472 4.7 0.115 1.5
LPS6225-472 4.7 0.065 3.2
Coiltronics^®
SD3110
4.7 0.285 0.68
SD3112
4.7 0.246 0.80
SD3114
4.7 0.251 1.14
SD3118
4.7 0.162 1.31
SD3812
4.7 0.256 1.13
SD25
4.7 0.0467 1.83
Size
WxLxH
(mm)
2.0x2.0x1.4
3.0x3.0x1.3
4.0x4.0x2.0
6.0x6.0x2.4
3.1x3.1x1.0
3.1x3.1x1.2
3.1x3.1x1.4
3.8x3.8x1.2
3.8x3.8x1.2
5.0x5.0x2.5
Part Number
Value
(µH)
DCR

(max)
Wurth Elektronik^®
WE-TPC Type 4.7 0.200
TH
WE-TPC Type 4.7 0.105
S
WE-TPC Type 4.7 0.082
M
WE-TPC Type 4.7 0.046
X
I_SAT
(A)
Size
WxLxH
(mm)
0.8 2.8x2.8x1.35
0.90 3.8x3.8x1.65
1.65 4.8x4.8x1.8
2.00 6.8x6.8x2.3
Part Number
Value
(µH)
Sumida^®
CMH23
4.7
CMD4D06
4.7
CDRH4D
4.7
EPCOS^®
B82462A2472 4.7
M000
B82462G4472 4.7
M
DCR

(max)
0.537
0.216
0.09
0.084
0.04
I_SAT
(A)
0.70
0.75
0.800
2.00
1.8
Size
WxLxH
(mm)
2.3x2.3x1.0
3.5x4.3x0.8
4.6x4.6x1.5
6.0x6.0x2.5
6.3x6.3x3.0
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.
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.
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, (_JA), the junction temperature
is estimated. The maximum continuous junction
temperature rating for the MCP1640/B/C/D is +125^oC.
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 Equation 5-3.
EQUATION 5-3:


V_{----O--E---U-f--f--Ti--c---}_i--e--I_{-n--O-c---Uy-----T--}
– VOUT  IOUT
=
PDis
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_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_INRMS2*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.
DS22234B-page 16
 2011 Microchip Technology Inc.