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| MB39C011APFT-G-BND-ERE1 Datasheet, PDF (35/53 Pages) Cypress Semiconductor – 2 ch DC/DC Converter IC with Synchronous Rectification | |||
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MB39C011A
19. Part Selection
19.1 Coil selection
As a rough guide, choose the inductance of the coil such that the peak-to-peak ripple current of the coil is less than 50ï¥ of the
maximum load current. The inductance in this case is given by the following formula.
Lâ¥
VIN ï VO
LOR ï´ï IOMAX
ï´
VO
VIN ï´ï fosc
L
IOMAX
LOR
VIN
VO
fosc
: Coil inductance [H]
: Maximum load current [A]
: 0.5
: Switching system power-supply voltage [V]
: Output voltage setting [V]
: Oscillation frequency [Hz]
When the IC is used with asynchronous rectification, it is recommended that the IC be used in the load current range where the
coil current is continuous in order to ensure responsiveness to the load. For asynchronous rectification it is therefore recommended
that the minimum value of the load current is used as the basis for setting the inductance value.
Lâ¥
VIN ï VO
2 ï´ï IOMIN
ï´
VO
VIN ï´ï fosc
L
IOMIN
VIN
VO
fosc
: Coil inductance [H]
: Minimum load current [A]
: Switching system power-supply voltage [V]
: Output voltage setting [V]
: Oscillation frequency [Hz]
The maximum value of the current flowing through the coil needs to be found in order to determine whether the current flowing
through the coil is within the rated value. The maximum current flowing through the coil is given by the following formula.
ILMAX ï½ IOMAX ï«
ïIL
2
ïIL â¥
VIN ï VO
L
ï´
VO
VIN ï´ï fosc
Coil current
ILMAX
IOMAX
IOMIN
0
The coil current changes
according to the load current.
ÎIL
Time
Document Number: 002-08369 Rev. *A
Page 35 of 53
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