Datasheet

© 2007 Microchip Technology Inc. DS22061A-page 15
MCP1602
Table 5-1 contains the recommend range for the output
capacitor value.
5.6 Inductor Selection
For most applications an inductor value of 4.7 µH is
recommended to achieve a good balance between
converter load transient response and minimized
noise. There are many different magnetic core
materials and package options to select from. That
decision is based on size, cost, and acceptable
radiated energy levels. Toroid and shielded ferrite pot
cores will have low radiated energy, but tend to be
larger and higher in cost.
The value of inductance is selected to achieve a
desired amount of ripple current. It is reasonable to
assume a ripple current that is 20% of the maximum
load current. The larger the amount of ripple current
allowed, the larger the output capacitor value becomes
to meet ripple voltage specifications. The inductor
ripple current can be calculated according to
Equation 5-4.
EQUATION 5-4:
When considering inductor ratings, the maximum DC
current rating of the inductor should be at least equal to
the maximum load current, plus one half the peak-to-
peak inductor ripple current (1/2 * ΔI
L
). The inductor DC
resistance adds to the total converter power loss. An
inductor with a low DC resistance allows for higher
converter efficiency.
5.7 Thermal Calculations
The MCP1602 is available in two different packages
(MSOP and 3x3 DFN). By calculating the power
dissipation and applying the package thermal
resistance, (θ
JA
), the junction temperature is
estimated. The maximum continuous junction
temperature rating for the MCP1602 is +125
o
C.
To quickly estimate the internal power dissipation for
the switching buck regulator, an empirical calculation
using measured efficiency can be used. Given the
measured efficiency, the internal power dissipation is
estimated by:
EQUATION 5-5:
The difference between the first term, input power
dissipation, and the second term, power delivered, is
the internal power dissipation. This is an estimate
assuming that most of the power lost is internal to the
MCP1602. There is some percentage of power lost in
the buck inductor, with very little loss in the input and
output capacitors.
TABLE 5-1: CAPACITOR VALUE RANGE
C
IN
C
OUT
Minimum 4.7 µF 4.7 µF
Maximum — 22 µF
TABLE 5-2: MCP1602 RECOMMENDED
INDUCTORS
Part
Number
Value
(µH)
DCR
Ω
(max)
I
SAT
(A)
Size
WxLxH (mm)
Coiltronics®
SD10 3.3 0.108 1.31 5.2x5.2x1.0
SD10 4.7 0.154 1.08 5.2x5.2x1.0
SD10 6.2 0.218 0.92 5.2x5.2x1.0
SD12 3.3 0.104 1.42 5.2x5.2x1.2
SD12 4.7 0.118 1.29 5.2x5.2x1.2
SD12 6.2 0.170 1.08 5.2x5.2x1.2
ΔI
L
V
OUT
F
SW
L×
-------------------
1
V
OUT
V
IN
-------------–
⎝⎠
⎛⎞
×=
Where:
F
SW
= Switching Frequency
Wurth Elektronik®
WE-TPC
Type S
3.6 0.085 1.10 3.8x3.8x1.65
WE-TPC
Type S
4.7 0.105 0.90 3.8x3.8x1.65
WE-TPC
Type S
6.8 0.156 0.75 3.8x3.8x1.65
WE-TPC
Type M
3.3 0.065 1.80 4.8x4.8x1.8
WE-TPC
Type M
4.7 0.082 1.65 4.8x4.8x1.8
WE-TPC
Type M
6.8 0.100 1.25 4.8x4.8x1.8
TABLE 5-2: MCP1602 RECOMMENDED
INDUCTORS (CONTINUED)
Part
Number
Value
(µH)
DCR
Ω
(max)
I
SAT
(A)
Size
WxLxH (mm)
V
OUT
I
OUT
×
Efficiency
-------------------------------
⎝⎠
⎛⎞
V
OUT
I
OUT
×()– P
Dis
=