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| MB39C011APFT-G-BND-ERE1 Datasheet, PDF (36/53 Pages) Cypress Semiconductor – 2 ch DC/DC Converter IC with Synchronous Rectification | |||
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MB39C011A
ILMAX
IOMAX
ïIL
L
VIN
VO
fosc
: Maximum coil current [A]
: Maximum load current [A]
: Coil ripple current peak to peak value [A]
: Coil inductance [H]
: Switching system power-supply voltage [V]
: Output setting voltage [V]
: Oscillation frequency [Hz]
19.2 SW FET selection
The maximum value of the current flowing through the SW FET needs to be found in order to determine whether the current flowing
through the SW FET is within the rated value. The maximum current flowing through the
SW FET is given by the following formula.
IDMAX ⥠IOMAX ï«
ïIL
2
IDMAX
IOMAX
ïIL
: Maximum SW FET drain current [A]
: Maximum load current [A]
: Coil ripple current peak to peak value [A]
Furthermore, the power dissipation of the SW FET needs to be found in order to determine whether the power dissipation of the
SW FET is within the rated value. The power dissipation of the SW FET is given by the following formula.
High side FET (P-ch MOS FET) power dissipation PHiSideFET ï½ PRon ï« PSW
PRon : High side FET (P-ch MOS FET) conduction loss
PRon ï½ IOMAX2ï´
VO
VIN
ï´Ron
IOMAX
VIN
VO
Ron
: Maximum load current [A]
: Switching system power supply voltage [V]
: Output voltage [V]
: High side FET ON resistance [ï]
PSW : High side FET (P-ch MOS FET) switching loss
PSW ï½
VIN ï´ï fOSC (Ibtm ï´ï tr ï´ï Itop ï´ï tf)
2
VIN : Switching system power supply voltage [V]
fosc : Oscillation frequency [Hz]
Ibtm : Bottom value of ripple current of coil [A]
Ibtm ï½ IOMAX ï
ïIL
2
Itop :Top value of ripple current of coil [A]
Itop ï½ IOMAX ï«
ïIL
2
Document Number: 002-08369 Rev. *A
Page 36 of 53
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