Datasheet

CPRI_ch CPRI
PRI
PRI
I × t
C
V
=
D
PRI
CPRI
PRI PRI
SW SW
IL _pospk
D (1 - D)
t + x
f f IL _pospk - IL _negpk
»
PRI
PRI PRI
CPRI_ch CPRI
IL _pospk
D + (1 - D) x
IL _pospk - IL _negpk
I IL _pospk x
3
»
CPRI_rms
I = ILrms
HS LSILrms I _ rms+ I _ rms»
( )
1
2
2
SEC
2
SEC
PRI PRI
OUT
OUT
Im_ripple x I x N
N
3 × D-1 1 - D
Ils _ rms × I x + + × Im_ripple
3 × 1-D N 3 x N 12
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1
2
2
2
SEC
OUT
PRI
N
D
Ihs _ rms D × I + × Im_ ripple
N 12
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( )
IN
OPRI
sw
V × D × 1 - D
Im_ ripple =
× Lf
( )
SEC
IN
OUT
PRI
OPRI
sw
N
V × D × 1-D
1 + D
ILpri _ negpk - I × -
N 1 - D 2 × × L
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TPS55010
www.ti.com SLVSAV0A –APRIL 2011–REVISED JUNE 2011
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PRIMARY SIDE CAPACITOR
The ΔV
PRI
voltage should be less than 10% of V
PRI
. The rated RMS current of C
PRI
should be greater than
Equation 22. It is desirable to have a larger primary capacitance to minimize ripple but this will slow the transient
response. For this design example, assuming the ΔV
PRI
is 0.22 V, the primary side capacitance is 4.74 µF and
the rms current is 1.04 A. A 4.7 µF/10V X5R ceramic capacitor is used.
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